json_view: fix GCC useless-cast, MSVC C4127, and MinGW object size

- drop the redundant int cast of the promoted uint16_t shift (-Wuseless-cast) - route the constant part of the float-pair condition through enabled() (C4127) - split unit-json_view_dump.cpp in three files for the MinGW assembler Signed-off-by: Niels Lohmann <mail@nlohmann.me>
json_view: dump canada.json faster than yyjson (batched float decisions)
2026-10-25 12:04:42 +00:00 · 2026-10-25 10:45:57 +01:00 · 2026-10-25 07:23:43 +01:00 · 2026-10-25 07:23:42 +01:00
10 changed files with 2010 additions and 874 deletions
@@ -23,10 +23,6 @@ Linear in [`node_count()`](node_count.md) plus the length of the decoded strings

 ## Notes

-The node index of a small document (an estimate of up to 1024 nodes, which is up to about 4 KiB of minified text) is
-allocated together with the document's header, so that parsing needs one allocation. That part cannot be released
-separately: `shrink_to_fit()` only trims a node index that has its own allocation, and the decoded strings.
-
 !!! warning "Invalidates views"

    Unlike moving the document, `shrink_to_fit()` **invalidates every view taken from this document before the
@@ -543,15 +543,7 @@ run_found:
    NLOHMANN_VIEW_NOINLINE void arena_grow(std::size_t n)
    {
        const std::size_t used = arena_used();
-        std::size_t wanted = used + n + 256;
-        if (m_doc.arena.empty())
-        {
-            // the first growth: a decoded string is never longer than its source,
-            // so a fraction of the input (capped, as the buffer is zero-filled)
-            // covers the escapes of a typical document without regrowing it
-            wanted = (std::max)(wanted, (std::min)(static_cast<std::size_t>(m_end - m_begin) / 4 + 16, std::size_t{4096}));
-        }
-        m_doc.arena.resize((std::max)(m_doc.arena.size() * 2, wanted));
+        m_doc.arena.resize((std::max)(m_doc.arena.size() * 2, used + n + 256));
        m_arena_write = m_doc.arena.data() + used;
        m_arena_end = m_doc.arena.data() + m_doc.arena.size();
    }
@@ -82,17 +82,14 @@ struct document_data
    };
    std::unique_ptr<edit_state> edits; ///< created by the first edit

-    /// the most nodes that are allocated together with the header (16 KiB)
-    static constexpr std::size_t max_inline_nodes = 1024;
-
    /// One allocation for the header and room for `count` nodes, so that a
    /// small document needs one allocation instead of two. Large documents get
    /// a separate node array instead (so it can be trimmed). When a document
-    /// outgrows the inline array, that array stays unused: at most 1024 nodes
-    /// (16 KiB), and only for documents whose estimate was too small.
+    /// outgrows the inline array, that array stays unused: at most 256 nodes
+    /// (4 KiB), and only for documents whose estimate was too small.
    static document_data* create(std::size_t count)
    {
-        count = count <= max_inline_nodes ? count : 0;
+        count = count <= 256 ? count : 0;
        void* mem = ::operator new (sizeof(document_data) + (count * sizeof(node)));
        auto* d = new (mem) document_data(); // NOLINT(cppcoreguidelines-owning-memory): owned by the returned pointer, freed by deleter
        // (aligned: sizeof is a multiple of the alignment; through void*, as GCC's -Wcast-align wants)
@@ -19,6 +19,7 @@
 #include <nlohmann/detail/view/macro_scope.hpp>
 #include <nlohmann/detail/view/node.hpp>
 #include <nlohmann/detail/view/scan.hpp>
+#include <nlohmann/detail/view/simd.hpp>

 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -103,12 +104,56 @@ NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
    return convert_float<FloatType>(first, last, dot, mantissa_end);
 }

+#if NLOHMANN_VIEW_VECTOR
+/*!
+@brief the value of the first 16 digits of a run of digits with a point after
+int_digits of them (or none, if int_digits >= 16)
+
+The 17 bytes at p are read at once: the bytes after the point move down by one,
+then pairs, quadruples, and octets of digits are combined by multiplications
+(after simdjson). The bytes [p, p + 32) must be readable. Bytes that are not
+digits (only in a damaged image loaded with image_check::bounds) give a wrong
+value, but no undefined behavior.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t sixteen_digits(const unsigned char* p, unsigned int_digits) noexcept
+{
+#if NLOHMANN_VIEW_NEON
+    const uint8x16_t low = vld1q_u8(p);
+    const uint8x16_t index = vcombine_u8(vcreate_u8(0x0706050403020100u), vcreate_u8(0x0F0E0D0C0B0A0908u));
+    const uint8x16_t before_point = vcltq_u8(index, vdupq_n_u8(static_cast<std::uint8_t>(int_digits)));
+    const uint8x16_t digits = vsubq_u8(vbslq_u8(before_point, low, vextq_u8(low, vld1q_u8(p + 16), 1)), vdupq_n_u8('0'));
+    const uint16x8_t twos = vpaddlq_u8(vmulq_u8(digits, vreinterpretq_u8_u16(vdupq_n_u16(0x010A))));
+    const uint32x4_t fours = vpaddlq_u16(vmulq_u16(twos, vreinterpretq_u16_u32(vdupq_n_u32(0x00010064))));
+    const uint64x2_t eights = vpaddlq_u32(vmulq_u32(fours, vreinterpretq_u32_u64(vdupq_n_u64(0x0000000100002710u))));
+    return (vgetq_lane_u64(eights, 0) * 100000000u) + vgetq_lane_u64(eights, 1);
+#else
+    // NOLINTBEGIN(portability-simd-intrinsics)
+    const __m128i low = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+    const __m128i high = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p + 16))); // NOLINT(bugprone-casting-through-void)
+    const __m128i before_point = _mm_cmpgt_epi8(_mm_set1_epi8(static_cast<char>(int_digits)), _mm_setr_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15));
+    const __m128i moved = _mm_or_si128(_mm_srli_si128(low, 1), _mm_slli_si128(high, 15));
+    const __m128i digits = _mm_sub_epi8(_mm_or_si128(_mm_and_si128(before_point, low), _mm_andnot_si128(before_point, moved)), _mm_set1_epi8('0'));
+    // (16-bit lanes: SSE2 has no multiply-add of bytes)
+    const __m128i tens = _mm_setr_epi16(10, 1, 10, 1, 10, 1, 10, 1);
+    const __m128i twos = _mm_packs_epi32(_mm_madd_epi16(_mm_unpacklo_epi8(digits, _mm_setzero_si128()), tens),
+                                         _mm_madd_epi16(_mm_unpackhi_epi8(digits, _mm_setzero_si128()), tens));
+    const __m128i fours = _mm_madd_epi16(twos, _mm_setr_epi16(100, 1, 100, 1, 100, 1, 100, 1));
+    const __m128i eights = _mm_madd_epi16(_mm_packs_epi32(fours, fours), _mm_setr_epi16(10000, 1, 10000, 1, 10000, 1, 10000, 1));
+    const auto upper = static_cast<std::uint32_t>(_mm_cvtsi128_si32(eights));
+    const auto lower = static_cast<std::uint32_t>(_mm_cvtsi128_si32(_mm_srli_si128(eights, 4)));
+    // NOLINTEND(portability-simd-intrinsics)
+    return (std::uint64_t{upper} * 100000000u) + lower;
+#endif
+}
+#endif
+
 /*!
@brief the digits of a float token with at most 19 digits, from its layout

 The digit layout recorded while parsing says where the integer digits, the
 fraction digits, and the exponent are, so the digits are read eight at a
-time without scanning.
+time without scanning (with SIMD, a token of 16 to 19 digits sixteen at a
+time).

@param[in] p  first character of the token
@param[in] e  end of the token
@@ -118,15 +163,34 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 {
    const bool negative = *p == '-';
    p += negative ? 1 : 0;
-    std::uint64_t w = parse_upto19(p, int_digits, limit);
-    p += int_digits;
+    std::uint64_t w = 0;
    std::int64_t q = 0;
-    if (frac_digits != 0)
+#if NLOHMANN_VIEW_VECTOR
+    const unsigned count = int_digits + frac_digits;
+    if (count >= 16 && limit - p >= 32)
    {
-        w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
-        p += 1 + frac_digits;
+        // (the point, if any, follows the integer digits; the digits after
+        // the first 16 are at most three)
+        w = sixteen_digits(p, int_digits);
+        for (unsigned i = 16; i < count; ++i)
+        {
+            w = (w * 10) + static_cast<std::uint64_t>(p[i + (i >= int_digits ? 1 : 0)] - '0');
+        }
+        p += count + (frac_digits != 0 ? 1 : 0);
        q = -static_cast<std::int64_t>(frac_digits);
    }
+    else
+#endif
+    {
+        w = parse_upto19(p, int_digits, limit);
+        p += int_digits;
+        if (frac_digits != 0)
+        {
+            w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
+            p += 1 + frac_digits;
+            q = -static_cast<std::int64_t>(frac_digits);
+        }
+    }
    if (p != e)
    {
        // [eE][+-]digits; huge exponents saturate (the parser rejected
@@ -161,12 +225,22 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 The result is correctly rounded by the lexer's conversion
 (detail::decimal_to_float(): Clinger's fast path where both operands are
 exact, else the Eisel-Lemire algorithm, which needs no fallback for up to 19
-digits), so it is the value parse() produces.
+digits), so it is the value parse() produces. Tokens of 16 or more digits go
+to Eisel-Lemire directly: the fast path takes few of them (none of 17 digits),
+and its check is a branch that data like GeoJSON coordinates mispredicts.
 */
 template<typename FloatType>
 NLOHMANN_VIEW_ALWAYS_INLINE FloatType layout_float(const unsigned char* p, const unsigned char* e, unsigned int_digits, unsigned frac_digits, const unsigned char* limit) noexcept
 {
-    return decimal_to_float<FloatType>(layout_decimal(p, e, int_digits, frac_digits, limit));
+    const float_significand d = layout_decimal(p, e, int_digits, frac_digits, limit);
+    if (int_digits + frac_digits >= 16)
+    {
+        using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+        native_float_t<FloatType> value{};
+        float_from_bits(eisel_lemire<format>(d.exponent, d.w) | (d.negative ? (std::uint64_t{1} << format::sign_bit()) : 0u), value);
+        return value;
+    }
+    return decimal_to_float<FloatType>(d);
 }

 /// the value of a float set by an edit: its token (the shortest round-trip
@@ -185,6 +259,80 @@ NLOHMANN_VIEW_NOINLINE FloatType edited_float(const char* token, const node& n)
    return float_value<FloatType>(token, n);
 }

+#if NLOHMANN_VIEW_VECTOR
+/// eisel_lemire() for the token w * 10^q of coordinate_float()
+template<typename Format>
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, Format /*format*/) noexcept
+{
+    return eisel_lemire<Format>(q, w);
+}
+
+/*!
+@brief (binary64) eisel_lemire() without the cases that tokens of 16 or 17
+digits with 5 or more after the point cannot reach: a value of 0, a
+subnormal, an infinity, or a tie (q < -4)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, ieee_binary_format<53> format) noexcept
+{
+    if (NLOHMANN_VIEW_UNLIKELY(w == 0 || q > -5))
+    {
+        return eisel_lemire<ieee_binary_format<53>>(q, w);
+    }
+    static_cast<void>(format);
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    std::uint64_t mantissa = high >> (upperbit + 9);
+    std::uint64_t power2 = static_cast<std::uint64_t>(((217706 * q) >> 16) + 63 + static_cast<std::int64_t>(upperbit) - lz + 1023);
+    mantissa = (mantissa + (mantissa & 1u)) >> 1u;
+    const bool carry = mantissa >= (std::uint64_t{2} << 52u);
+    mantissa = carry ? (std::uint64_t{1} << 52u) : mantissa;
+    power2 += carry ? 1u : 0u;
+    return (mantissa & ~(std::uint64_t{1} << 52u)) | (power2 << 52u);
+}
+
+/*!
+@brief (binary32 and binary64) the value of a float token of the source with
+16 or 17 digits, a point, and no exponent, the shape of most coordinates
+written with full precision; whether the token of n has this shape
+
+These tokens skip the general layout of layout_decimal(): no digits beyond
+the 17th, no exponent (and Eisel-Lemire directly, as in layout_float()).
+*/
+template<typename FloatType>
+NLOHMANN_VIEW_ALWAYS_INLINE bool coordinate_float(const document_data& d, const node& n, FloatType& value) noexcept
+{
+    const unsigned int_digits = n.extra & 0xFFu;
+    const unsigned frac_digits = n.extra >> 8u;
+    const unsigned count = int_digits + frac_digits;
+    const auto* const first = reinterpret_cast<const unsigned char*>(d.src + n.off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const unsigned negative = first[0] == '-' ? 1u : 0u;
+    if (count - 16u > 1u || frac_digits == 0 || n.len != negative + count + 1 || d.size - n.off < 33)
+    {
+        return false;
+    }
+    const unsigned char* const digits = first + negative;
+    const std::uint64_t w = sixteen_digits(digits, int_digits);
+    // (the 17th digit follows the point)
+    const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(digits[17] - '0');
+    using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+    native_float_t<FloatType> result{};
+    float_from_bits(coordinate_bits(-static_cast<std::int64_t>(frac_digits), count == 17 ? w17 : w, format{}) | (static_cast<std::uint64_t>(negative) << format::sign_bit()), result);
+    value = result;
+    return true;
+}
+
+#endif
+
 /// the value of the float token of a node, as parse() converts it; floats and
 /// doubles with at most 19 digits are converted from the digit layout
 template<typename FloatType>
@@ -200,6 +348,13 @@ FloatType float_value(const document_data& d, const node& n)
 template<typename FloatType>
 FloatType float_value(const document_data& d, const node& n, std::true_type /*binary32 or binary64*/)
 {
+#if NLOHMANN_VIEW_VECTOR
+    FloatType value {};
+    if (coordinate_float(d, n, value))
+    {
+        return value;
+    }
+#endif
    const unsigned int_digits = n.extra & 0xFFu;
    const unsigned frac_digits = n.extra >> 8u;
    if (NLOHMANN_VIEW_LIKELY(int_digits + frac_digits <= 19)) // (255 marks "many")
@@ -14,7 +14,9 @@
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy, memset
+#include <functional> // less
 #include <limits> // numeric_limits
+#include <memory> // unique_ptr
 #include <type_traits> // integral_constant
 #include <vector> // vector

@@ -384,6 +386,127 @@ struct depth_counter<false>
    }
 };

+/*!
+@brief where the double x nearest to a token w * 10^q lies, for 10^15 <= w <
+10^17 and -17 <= q <= -1 (Eisel-Lemire, then a fixed-point position)
+
+dump() writes the shortest decimal in the rounding interval of x (the closest
+one if there are several, see zmij::to_shortest()). Its digits are those of a
+multiple of 10^g of the token's last digit, with g = dec_exp + 1 - q for x's
+decimal exponent dec_exp: the multiple of 10^g nearest to x if it lies in the
+interval (at most one does), else the multiple of 10^(g - 1) nearest to x
+(see token_digits_1() and token_digits_2()). For g <= 0, the token itself is
+in the interval.
+
+The position is exact in a 64-bit fixed-point number with 56 bits after the
+point (of the token's last digit): x / 10^q = 2c * 5^-q / 2^t for x = c * 2^e2
+and t = q + 1 - e2, with at most 56 bits after the point here, and |x / 10^q -
+w| is at most half the spacing of the doubles, below 12 units. So only the low
+64 bits of 2c * 5^-q are needed. c and e2 come from Eisel-Lemire's product
+directly (as eisel_lemire() rounds it: no tie is possible for q < -4, and its
+second product is added where it can carry into the result).
+
+@param[out] offset  x / 10^q - w + 32, with 56 bits after the point
+@param[out] radius  half the spacing of the doubles at x, likewise (+ 1 if
+                    the interval is closed)
+@return g; 3 if the digits are not decided here (a power of two, whose
+        interval is not symmetric, or out of range)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE int locate_token(std::uint64_t w, int q, std::uint64_t& offset, std::uint64_t& radius) noexcept
+{
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (as eisel_lemire(): the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    const std::uint64_t mantissa = high >> (upperbit + 9);
+    const std::uint64_t c = (mantissa + (mantissa & 1u)) >> 1u;
+    // e2 as eisel_lemire() computes the exponent (log2(10) ~ 217706 / 2^16)
+    const int e2 = static_cast<int>((217706 * static_cast<std::int64_t>(q)) >> 16) + 63 + static_cast<int>(upperbit) - lz - 52;
+    const int t = q + 1 - e2;
+    const int g = ((e2 * 315653) >> 20) + 1 - q; // (dec_exp as in zmij::to_shortest(), for a regular x)
+    static const std::array<std::uint64_t, 17> fives = {{1u, 5u, 25u, 125u, 625u, 3125u, 15625u, 78125u, 390625u, 1953125u, 9765625u, 48828125u, 244140625u, 1220703125u, 6103515625u, 30517578125u, 152587890625u}};
+    const std::uint64_t five = fives[static_cast<std::size_t>(-q)]; // 5^-q
+    const unsigned s = static_cast<unsigned>(56 - t) & 63u;
+    offset = ((2 * c * five) << s) - (w << 56u) + (std::uint64_t{32} << 56u);
+    radius = (five << s) + ((c & 1u) == 0 ? 1u : 0u);
+    // (c = 2^52: a power of two; c = 2^53: rounded up to one. With 8 to 16
+    // fraction digits, as the batch's tokens have, t is in [15, 40] and g at
+    // most 2. x lies halfway between two candidates only if its distance from
+    // the token is a whole unit (g == 2) or a half (g == 1): such tokens are
+    // left to the full conversion)
+    const bool decided = c - ((std::uint64_t{1} << 52u) + 1) < (std::uint64_t{1} << 52u) - 1
+                         && (offset & ((std::uint64_t{1} << 55u) - 1)) != 0;
+    return decided ? g : 3;
+}
+
+/// the distance of a position (see locate_token()) from the biased point 32
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t biased_distance(std::uint64_t position) noexcept
+{
+    constexpr std::uint64_t center = std::uint64_t{32} << 56u;
+    return position >= center ? position - center : center - position;
+}
+
+/*!
+@brief (g == 1) the digits dump() writes for a token, from the position of its
+double (see locate_token()): the multiple of 10 nearest to x if it is in the
+interval, else w rounded to x (an exact tie between two candidates, like
+754570942.33984373, whose double is 754570942.33984375, is excluded by
+locate_token())
+
+With |x - w| at most the radius, which is below half the spacing of the
+candidates, the multiple of 10 nearest to x is w - r10 or the one above it.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_1(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r10 * one); // x - (w - r10) (+ 32)
+    const bool up = from > 37 * one;                  // (nearer to the multiple above)
+    const bool shorter = biased_distance(from - (up ? 10 * one : 0)) < radius;
+    const std::uint64_t a = w - r10 + (up ? 10u : 0u);
+    const std::uint64_t b = w + ((offset + (one / 2)) >> 56u) - 32;                // w rounded to x
+    return shorter ? a : b;
+}
+
+/*!
+@brief (g == 2) the digits dump() writes for a token, as token_digits_1(): the
+multiple of 100 nearest to x if it is in the interval, else the multiple of 10
+nearest to x
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_2(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10, std::uint64_t r100) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r100 * one);
+    const bool up = from > 82 * one;
+    const bool shorter = biased_distance(from - (up ? 100 * one : 0)) < radius;
+    const std::uint64_t a = w - r100 + (up ? 100u : 0u);
+    // x - (w - r10), in [-12, 21]: the multiple of 10 nearest to x is that one,
+    // or one or two above, or one below
+    const std::uint64_t y = offset + (r10 * one);
+    const std::uint64_t steps = (y > 37 * one ? 1u : 0u) + (y > 47 * one ? 1u : 0u);
+    const bool down = y < 27 * one;
+    const std::uint64_t b = w - r10 + (10 * steps) - (down ? 10u : 0u);
+    return shorter ? a : b;
+}
+
+/// the four ASCII digits of x < 10^4, the first in the lowest byte (as
+/// little-endian memory holds them)
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint32_t four_digit_text(std::uint32_t x) noexcept
+{
+    const std::uint32_t ab = (x * 5243u) >> 19u; // x / 100
+    std::uint32_t v = ab | ((x - (ab * 100u)) << 16u);
+    const std::uint32_t a = ((v * 103u) >> 10u) & 0x000F000Fu; // / 10 per 16-bit lane
+    v = a | ((v - (a * 10u)) << 8u);
+    return v + 0x30303030u;
+}
+
 /// how the view's dump() writes a value
 struct dump_style
 {
@@ -711,6 +834,7 @@ class view_serializer
        std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
        std::vector<frame> heap;
        small_stack<frame> stack(buffer.data(), buffer.size(), heap);
+        float_batch batch;
        const char* const src = m_doc.src;
        const char* const src_end = src + m_doc.size;
        char* w = m_out.cursor();
@@ -850,7 +974,7 @@ class view_serializer
                    else if (enabled(fast_double::value))
                    {
                        room(64);
-                        w = write_double_at(w, *n);
+                        w = write_double_ahead(w, src, n, batch);
                    }
                    else
                    {
@@ -875,6 +999,20 @@ class view_serializer
                case value_t::array:
                {
                    const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
+                    // (read-only documents, compact output) a pair of floats,
+                    // like the coordinates of GeoJSON, without a frame
+                    if (enabled(!Editable && !Pretty && !SourceNumbers && fast_double::value) && n->next == 3 && n->len == 2
+                            && n[1].kind == static_cast<std::uint8_t>(value_t::number_float) && n[2].kind == static_cast<std::uint8_t>(value_t::number_float))
+                    {
+                        room(2 * 64);
+                        *w++ = '[';
+                        w = write_double_ahead(w, src, n + 1, batch);
+                        *w++ = ',';
+                        w = write_double_ahead(w, src, n + 2, batch);
+                        *w++ = ']';
+                        n += 2; // (the element before the next node)
+                        break;
+                    }
                    room(8);
                    if (n->len == 0)
                    {
@@ -984,6 +1122,247 @@ class view_serializer
        }
    }

+    /// (float_batch) the mark of digits whose rounding carried beyond the
+    /// token's last four (see mark())
+    static constexpr std::uint64_t carried() noexcept
+    {
+        return std::uint64_t{1} << 63u;
+    }
+
+    /// floats of 16 or 17 digits ahead of the walk, converted together (see
+    /// convert_ahead()), with their digits as mark() keeps them
+    struct float_batch
+    {
+        static constexpr std::size_t capacity() noexcept
+        {
+            return 256;
+        }
+        /// (on the heap, allocated by the first conversion: a frame of more
+        /// than a page made every dump of a small document slower)
+        struct entries
+        {
+            std::array<const node*, 256> at; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+            std::array<std::uint64_t, 256> digits; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        };
+        std::unique_ptr<entries> storage{};
+        const node** at = nullptr;
+        std::uint64_t* digits = nullptr;
+        std::size_t count = 0;
+        std::size_t next = 0;
+        const node* scanned = nullptr; ///< where the last scan of the node array ended
+    };
+
+    /// (doubles) the float at n as dump() writes it, at w (64 bytes of room):
+    /// from the batch if it holds n
+    NLOHMANN_VIEW_ALWAYS_INLINE char* write_double_ahead(char* w, const char* src, const node* n, float_batch& batch)
+    {
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+        // (digits 0: not written by the batch; carried(): rounding carried
+        // beyond the last four digits)
+        if (batch.next != batch.count && batch.at[batch.next] == n && batch.digits[batch.next] - 1 < carried() - 1)
+        {
+            return write_token_digits(w, src, *n, batch.digits[batch.next++]);
+        }
+        return write_double_beside(w, n, batch);
+#else
+        static_cast<void>(src);
+        static_cast<void>(batch);
+        return write_double_at(w, *n);
+#endif
+    }
+
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+    /// write_double_ahead() for a float that is not the batch's next one (out
+    /// of line: the walk is faster with less code in its loop)
+    NLOHMANN_VIEW_NOINLINE char* write_double_beside(char* w, const node* n, float_batch& batch)
+    {
+        // (an editable document's walk can skip nodes of the array)
+        const std::less<const node*> before;
+        while (batch.next != batch.count && before(batch.at[batch.next], n))
+        {
+            ++batch.next;
+        }
+        if ((batch.next != batch.count && batch.at[batch.next] == n) || convert_ahead(n, batch))
+        {
+            const std::uint64_t digits = batch.digits[batch.next++];
+            if ((digits & carried()) != 0)
+            {
+                return write_carried_digits(w, *n, digits & ~carried());
+            }
+            if (digits != 0)
+            {
+                return write_token_digits(w, m_doc.src, *n, digits);
+            }
+        }
+        return write_double_at(w, *n);
+    }
+
+    /*!
+    @brief convert the floats of 16 or 17 digits among the next nodes of the
+    array at once; whether n is the first of them
+
+    Such tokens (like the coordinates of GeoJSON, written with 17 digits) are
+    written as the token with its last four digits replaced
+    (write_token_digits()). Each step (the digits, locate_token(),
+    token_digits_1/2()) is a long chain of dependent operations; one loop per
+    step over many floats lets the processor overlap the floats, which it does
+    not across the steps of one float (on Apple M1, one loop for the digits and
+    locate_token() made the dump of canada.json 12 % slower). Each node of the array
+    is scanned once; a node that the walk does not reach in order (in an
+    editable document) is written without the batch.
+    */
+    NLOHMANN_VIEW_NOINLINE bool convert_ahead(const node* n, float_batch& batch)
+    {
+        const std::less<const node*> before;
+        const node* const last = m_doc.nodes + m_doc.node_count;
+        if (before(n, batch.scanned) || before(n, m_doc.nodes) || !before(n, last))
+        {
+            return false;
+        }
+        const char* const src = m_doc.src;
+        const char* const src_end = src + m_doc.size;
+        const node* const stop = last - n > 1024 ? n + 1024 : last;
+        batch.count = 0;
+        batch.next = 0;
+        // the digits of each token (and its last four from the text)
+        std::array<std::uint64_t, 256> digits;     // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<int, 256> exponent;             // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint32_t, 256> last_four;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        const node* p = n;
+        if (!batch.storage)
+        {
+            batch.storage.reset(new typename float_batch::entries); // NOLINT(cppcoreguidelines-owning-memory,modernize-make-unique): C++11
+            batch.at = batch.storage->at.data();
+            batch.digits = batch.storage->digits.data();
+        }
+        for (; p != stop && batch.count != float_batch::capacity(); ++p)
+        {
+            // a token of the source: 16 or 17 digits, at least 8 after the
+            // point, no exponent, 32 bytes to read
+            const unsigned frac_digits = p->extra >> 8u;
+            const unsigned int_digits = p->extra & 0xFFu;
+            const unsigned count = int_digits + frac_digits;
+            if (p->kind == static_cast<std::uint8_t>(value_t::number_float) && (p->flags & node_flags::storage) == 0
+                    && count - 16u <= 1u && frac_digits >= 8 && src_end - (src + p->off) >= 33)
+            {
+                const auto* const token = reinterpret_cast<const unsigned char*>(src + p->off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+                const unsigned sign = token[0] == '-' ? 1 : 0;
+                const unsigned char* const first = token + sign;
+                const std::uint64_t w = sixteen_digits(first, int_digits);
+                // (the 17th digit follows the point; a token with an exponent
+                // gets digits outside the range of locate_token(), and is not
+                // written by the batch. A token 0.xxx with 16 significant
+                // digits is: its double is written as "0." and its digits too)
+                const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(first[17] - '0');
+                const std::size_t i = batch.count++;
+                batch.at[i] = p;
+                digits[i] = p->len != sign + count + 1 ? 0 : (count == 17 ? w17 : w);
+                exponent[i] = -static_cast<int>(frac_digits);
+                // (byte 0: the last digit, byte 1: the last two, bits 16-29: the last four)
+                std::uint32_t four = 0;
+                std::memcpy(&four, token + p->len - 4, 4);
+                four -= 0x30303030u;
+                const std::uint32_t pairs = ((four & 0x0F0F0F0Fu) * 2561u) >> 8u; // (byte 0, 2: the pairs)
+                last_four[i] = (four >> 24u) | ((pairs >> 16u & 0xFFu) << 8u) | ((((pairs & 0x00FF00FFu) * 6553601u) >> 16u) << 16u);
+            }
+        }
+        batch.scanned = p;
+        // the position of each double, and the floats of either kind
+        std::array<std::uint64_t, 256> offset; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint64_t, 256> radius; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_1;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_2;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::size_t count_1 = 0;
+        std::size_t count_2 = 0;
+        for (std::size_t i = 0; i != batch.count; ++i)
+        {
+            const std::uint64_t w = digits[i];
+            // (the range excludes the values of bytes that are not digits, only
+            // in a damaged image loaded with image_check::bounds)
+            const int g = w - 1000000000000000u < 99000000000000000u ? locate_token(w, exponent[i], offset[i], radius[i]) : 3;
+            batch.digits[i] = g <= 0 ? (last_four[i] >> 16u) + 1 : 0;
+            kind_1[count_1] = static_cast<std::uint8_t>(i);
+            count_1 += g == 1 ? 1 : 0;
+            kind_2[count_2] = static_cast<std::uint8_t>(i);
+            count_2 += g == 2 ? 1 : 0;
+        }
+        // the digits to write, in one loop per kind (see mark())
+        for (std::size_t k = 0; k != count_1; ++k)
+        {
+            const std::size_t i = kind_1[k];
+            const std::uint64_t s = token_digits_1(digits[i], offset[i], radius[i], last_four[i] & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        for (std::size_t k = 0; k != count_2; ++k)
+        {
+            const std::size_t i = kind_2[k];
+            const std::uint64_t s = token_digits_2(digits[i], offset[i], radius[i], last_four[i] & 0xFFu, (last_four[i] >> 8u) & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        return batch.count != 0 && batch.at[0] == n;
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room), from the digits of its double (see locate_token()) whose
+    rounding carried beyond the token's last four digits
+
+    (like 43.42027299999999 -> 43.420273): the digits go to the writer of
+    Zmij's results as its 15 or 16 leading digits and one more, which omits
+    the trailing zeros.
+    */
+    NLOHMANN_VIEW_NOINLINE char* write_carried_digits(char* w, const node& n, std::uint64_t digits) const noexcept
+    {
+        const int exponent = -(n.extra >> 8u);
+        const std::uint64_t leading = digits / 10;
+        const auto last = static_cast<unsigned char>(digits - (leading * 10));
+        const bool seventeen = digits >= 10000000000000000u;
+        *w = '-';
+        w += m_doc.src[n.off] == '-' ? 1 : 0;
+        return ::nlohmann::detail::dtoa_impl::write_shortest(w, seventeen ? ::nlohmann::detail::zmij::shortest_decimal{leading, exponent, last, last != 0}
+                : ::nlohmann::detail::zmij::shortest_decimal{digits, exponent - 1, 0, false});
+    }
+
+    /// the digits s of a token with the digits w and the last four digits
+    /// r4, as the batch keeps them: the new last four digits + 1 (only those
+    /// are written over the token's), or s marked if it differs from w beyond
+    /// them (0 stays for a float the batch does not write)
+    static std::uint64_t mark(std::uint64_t w, std::uint64_t s, std::uint64_t r4) noexcept
+    {
+        const std::uint64_t last = s - (w - r4);
+        return last < 10000 ? last + 1 : s | carried();
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room): the token with its last four digits replaced by digits - 1 (see
+    mark(); the others are the token's), and without trailing zeros after the
+    point, but one
+    */
+    char* write_token_digits(char* w, const char* src, const node& n, std::uint64_t digits)
+    {
+        const char* const token = src + n.off;
+        std::memcpy(w, token, 32);
+        char* const end = w + n.len;
+        const std::uint32_t last = four_digit_text(static_cast<std::uint32_t>(digits - 1));
+        std::memcpy(end - 4, &last, 4);
+        // (the token's text before the new digits, from the source: reading
+        // the output back would wait for the stores)
+        std::uint64_t before = 0;
+        std::memcpy(&before, token + n.len - 12, 8);
+        const std::uint32_t last_zeros = last ^ 0x30303030u;
+        const std::uint64_t before_zeros = before ^ 0x3030303030303030u;
+        if (NLOHMANN_VIEW_UNLIKELY(last_zeros == 0 && before_zeros == 0))
+        {
+            return write_double_at(w, n); // (twelve or more trailing zeros)
+        }
+        const unsigned zeros = last_zeros != 0 ? static_cast<unsigned>(count_leading_zeros(last_zeros)) / 8 - 4
+                               : 4 + (static_cast<unsigned>(count_leading_zeros(before_zeros)) / 8);
+        const unsigned frac_digits = n.extra >> 8u;
+        return end - (zeros < frac_digits ? zeros : frac_digits - 1);
+    }
+#endif
+
    /// a float node as dump() writes it
    void write_float_node(const node& n)
    {
@@ -397,17 +397,14 @@ struct document_data
    };
    std::unique_ptr<edit_state> edits; ///< created by the first edit

-    /// the most nodes that are allocated together with the header (16 KiB)
-    static constexpr std::size_t max_inline_nodes = 1024;
-
    /// One allocation for the header and room for `count` nodes, so that a
    /// small document needs one allocation instead of two. Large documents get
    /// a separate node array instead (so it can be trimmed). When a document
-    /// outgrows the inline array, that array stays unused: at most 1024 nodes
-    /// (16 KiB), and only for documents whose estimate was too small.
+    /// outgrows the inline array, that array stays unused: at most 256 nodes
+    /// (4 KiB), and only for documents whose estimate was too small.
    static document_data* create(std::size_t count)
    {
-        count = count <= max_inline_nodes ? count : 0;
+        count = count <= 256 ? count : 0;
        void* mem = ::operator new (sizeof(document_data) + (count * sizeof(node)));
        auto* d = new (mem) document_data(); // NOLINT(cppcoreguidelines-owning-memory): owned by the returned pointer, freed by deleter
        // (aligned: sizeof is a multiple of the alignment; through void*, as GCC's -Wcast-align wants)
@@ -1737,15 +1734,7 @@ run_found:
    NLOHMANN_VIEW_NOINLINE void arena_grow(std::size_t n)
    {
        const std::size_t used = arena_used();
-        std::size_t wanted = used + n + 256;
-        if (m_doc.arena.empty())
-        {
-            // the first growth: a decoded string is never longer than its source,
-            // so a fraction of the input (capped, as the buffer is zero-filled)
-            // covers the escapes of a typical document without regrowing it
-            wanted = (std::max)(wanted, (std::min)(static_cast<std::size_t>(m_end - m_begin) / 4 + 16, std::size_t{4096}));
-        }
-        m_doc.arena.resize((std::max)(m_doc.arena.size() * 2, wanted));
+        m_doc.arena.resize((std::max)(m_doc.arena.size() * 2, used + n + 256));
        m_arena_write = m_doc.arena.data() + used;
        m_arena_end = m_doc.arena.data() + m_doc.arena.size();
    }
@@ -4616,6 +4605,8 @@ NLOHMANN_JSON_NAMESPACE_END

 // #include <nlohmann/detail/view/scan.hpp>

+// #include <nlohmann/detail/view/simd.hpp>
+

 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
@@ -4700,12 +4691,56 @@ NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
    return convert_float<FloatType>(first, last, dot, mantissa_end);
 }

+#if NLOHMANN_VIEW_VECTOR
+/*!
+@brief the value of the first 16 digits of a run of digits with a point after
+int_digits of them (or none, if int_digits >= 16)
+
+The 17 bytes at p are read at once: the bytes after the point move down by one,
+then pairs, quadruples, and octets of digits are combined by multiplications
+(after simdjson). The bytes [p, p + 32) must be readable. Bytes that are not
+digits (only in a damaged image loaded with image_check::bounds) give a wrong
+value, but no undefined behavior.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t sixteen_digits(const unsigned char* p, unsigned int_digits) noexcept
+{
+#if NLOHMANN_VIEW_NEON
+    const uint8x16_t low = vld1q_u8(p);
+    const uint8x16_t index = vcombine_u8(vcreate_u8(0x0706050403020100u), vcreate_u8(0x0F0E0D0C0B0A0908u));
+    const uint8x16_t before_point = vcltq_u8(index, vdupq_n_u8(static_cast<std::uint8_t>(int_digits)));
+    const uint8x16_t digits = vsubq_u8(vbslq_u8(before_point, low, vextq_u8(low, vld1q_u8(p + 16), 1)), vdupq_n_u8('0'));
+    const uint16x8_t twos = vpaddlq_u8(vmulq_u8(digits, vreinterpretq_u8_u16(vdupq_n_u16(0x010A))));
+    const uint32x4_t fours = vpaddlq_u16(vmulq_u16(twos, vreinterpretq_u16_u32(vdupq_n_u32(0x00010064))));
+    const uint64x2_t eights = vpaddlq_u32(vmulq_u32(fours, vreinterpretq_u32_u64(vdupq_n_u64(0x0000000100002710u))));
+    return (vgetq_lane_u64(eights, 0) * 100000000u) + vgetq_lane_u64(eights, 1);
+#else
+    // NOLINTBEGIN(portability-simd-intrinsics)
+    const __m128i low = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+    const __m128i high = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p + 16))); // NOLINT(bugprone-casting-through-void)
+    const __m128i before_point = _mm_cmpgt_epi8(_mm_set1_epi8(static_cast<char>(int_digits)), _mm_setr_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15));
+    const __m128i moved = _mm_or_si128(_mm_srli_si128(low, 1), _mm_slli_si128(high, 15));
+    const __m128i digits = _mm_sub_epi8(_mm_or_si128(_mm_and_si128(before_point, low), _mm_andnot_si128(before_point, moved)), _mm_set1_epi8('0'));
+    // (16-bit lanes: SSE2 has no multiply-add of bytes)
+    const __m128i tens = _mm_setr_epi16(10, 1, 10, 1, 10, 1, 10, 1);
+    const __m128i twos = _mm_packs_epi32(_mm_madd_epi16(_mm_unpacklo_epi8(digits, _mm_setzero_si128()), tens),
+                                         _mm_madd_epi16(_mm_unpackhi_epi8(digits, _mm_setzero_si128()), tens));
+    const __m128i fours = _mm_madd_epi16(twos, _mm_setr_epi16(100, 1, 100, 1, 100, 1, 100, 1));
+    const __m128i eights = _mm_madd_epi16(_mm_packs_epi32(fours, fours), _mm_setr_epi16(10000, 1, 10000, 1, 10000, 1, 10000, 1));
+    const auto upper = static_cast<std::uint32_t>(_mm_cvtsi128_si32(eights));
+    const auto lower = static_cast<std::uint32_t>(_mm_cvtsi128_si32(_mm_srli_si128(eights, 4)));
+    // NOLINTEND(portability-simd-intrinsics)
+    return (std::uint64_t{upper} * 100000000u) + lower;
+#endif
+}
+#endif
+
 /*!
@brief the digits of a float token with at most 19 digits, from its layout

 The digit layout recorded while parsing says where the integer digits, the
 fraction digits, and the exponent are, so the digits are read eight at a
-time without scanning.
+time without scanning (with SIMD, a token of 16 to 19 digits sixteen at a
+time).

@param[in] p  first character of the token
@param[in] e  end of the token
@@ -4715,15 +4750,34 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 {
    const bool negative = *p == '-';
    p += negative ? 1 : 0;
-    std::uint64_t w = parse_upto19(p, int_digits, limit);
-    p += int_digits;
+    std::uint64_t w = 0;
    std::int64_t q = 0;
-    if (frac_digits != 0)
+#if NLOHMANN_VIEW_VECTOR
+    const unsigned count = int_digits + frac_digits;
+    if (count >= 16 && limit - p >= 32)
    {
-        w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
-        p += 1 + frac_digits;
+        // (the point, if any, follows the integer digits; the digits after
+        // the first 16 are at most three)
+        w = sixteen_digits(p, int_digits);
+        for (unsigned i = 16; i < count; ++i)
+        {
+            w = (w * 10) + static_cast<std::uint64_t>(p[i + (i >= int_digits ? 1 : 0)] - '0');
+        }
+        p += count + (frac_digits != 0 ? 1 : 0);
        q = -static_cast<std::int64_t>(frac_digits);
    }
+    else
+#endif
+    {
+        w = parse_upto19(p, int_digits, limit);
+        p += int_digits;
+        if (frac_digits != 0)
+        {
+            w = (w * int_pow10(frac_digits)) + parse_upto19(p + 1, frac_digits, limit);
+            p += 1 + frac_digits;
+            q = -static_cast<std::int64_t>(frac_digits);
+        }
+    }
    if (p != e)
    {
        // [eE][+-]digits; huge exponents saturate (the parser rejected
@@ -4758,12 +4812,22 @@ NLOHMANN_VIEW_ALWAYS_INLINE float_significand layout_decimal(const unsigned char
 The result is correctly rounded by the lexer's conversion
 (detail::decimal_to_float(): Clinger's fast path where both operands are
 exact, else the Eisel-Lemire algorithm, which needs no fallback for up to 19
-digits), so it is the value parse() produces.
+digits), so it is the value parse() produces. Tokens of 16 or more digits go
+to Eisel-Lemire directly: the fast path takes few of them (none of 17 digits),
+and its check is a branch that data like GeoJSON coordinates mispredicts.
 */
 template<typename FloatType>
 NLOHMANN_VIEW_ALWAYS_INLINE FloatType layout_float(const unsigned char* p, const unsigned char* e, unsigned int_digits, unsigned frac_digits, const unsigned char* limit) noexcept
 {
-    return decimal_to_float<FloatType>(layout_decimal(p, e, int_digits, frac_digits, limit));
+    const float_significand d = layout_decimal(p, e, int_digits, frac_digits, limit);
+    if (int_digits + frac_digits >= 16)
+    {
+        using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+        native_float_t<FloatType> value{};
+        float_from_bits(eisel_lemire<format>(d.exponent, d.w) | (d.negative ? (std::uint64_t{1} << format::sign_bit()) : 0u), value);
+        return value;
+    }
+    return decimal_to_float<FloatType>(d);
 }

 /// the value of a float set by an edit: its token (the shortest round-trip
@@ -4782,6 +4846,80 @@ NLOHMANN_VIEW_NOINLINE FloatType edited_float(const char* token, const node& n)
    return float_value<FloatType>(token, n);
 }

+#if NLOHMANN_VIEW_VECTOR
+/// eisel_lemire() for the token w * 10^q of coordinate_float()
+template<typename Format>
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, Format /*format*/) noexcept
+{
+    return eisel_lemire<Format>(q, w);
+}
+
+/*!
+@brief (binary64) eisel_lemire() without the cases that tokens of 16 or 17
+digits with 5 or more after the point cannot reach: a value of 0, a
+subnormal, an infinity, or a tie (q < -4)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t coordinate_bits(std::int64_t q, std::uint64_t w, ieee_binary_format<53> format) noexcept
+{
+    if (NLOHMANN_VIEW_UNLIKELY(w == 0 || q > -5))
+    {
+        return eisel_lemire<ieee_binary_format<53>>(q, w);
+    }
+    static_cast<void>(format);
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    std::uint64_t mantissa = high >> (upperbit + 9);
+    std::uint64_t power2 = static_cast<std::uint64_t>(((217706 * q) >> 16) + 63 + static_cast<std::int64_t>(upperbit) - lz + 1023);
+    mantissa = (mantissa + (mantissa & 1u)) >> 1u;
+    const bool carry = mantissa >= (std::uint64_t{2} << 52u);
+    mantissa = carry ? (std::uint64_t{1} << 52u) : mantissa;
+    power2 += carry ? 1u : 0u;
+    return (mantissa & ~(std::uint64_t{1} << 52u)) | (power2 << 52u);
+}
+
+/*!
+@brief (binary32 and binary64) the value of a float token of the source with
+16 or 17 digits, a point, and no exponent, the shape of most coordinates
+written with full precision; whether the token of n has this shape
+
+These tokens skip the general layout of layout_decimal(): no digits beyond
+the 17th, no exponent (and Eisel-Lemire directly, as in layout_float()).
+*/
+template<typename FloatType>
+NLOHMANN_VIEW_ALWAYS_INLINE bool coordinate_float(const document_data& d, const node& n, FloatType& value) noexcept
+{
+    const unsigned int_digits = n.extra & 0xFFu;
+    const unsigned frac_digits = n.extra >> 8u;
+    const unsigned count = int_digits + frac_digits;
+    const auto* const first = reinterpret_cast<const unsigned char*>(d.src + n.off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+    const unsigned negative = first[0] == '-' ? 1u : 0u;
+    if (count - 16u > 1u || frac_digits == 0 || n.len != negative + count + 1 || d.size - n.off < 33)
+    {
+        return false;
+    }
+    const unsigned char* const digits = first + negative;
+    const std::uint64_t w = sixteen_digits(digits, int_digits);
+    // (the 17th digit follows the point)
+    const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(digits[17] - '0');
+    using format = ieee_binary_format<std::numeric_limits<FloatType>::digits>;
+    native_float_t<FloatType> result{};
+    float_from_bits(coordinate_bits(-static_cast<std::int64_t>(frac_digits), count == 17 ? w17 : w, format{}) | (static_cast<std::uint64_t>(negative) << format::sign_bit()), result);
+    value = result;
+    return true;
+}
+
+#endif
+
 /// the value of the float token of a node, as parse() converts it; floats and
 /// doubles with at most 19 digits are converted from the digit layout
 template<typename FloatType>
@@ -4797,6 +4935,13 @@ FloatType float_value(const document_data& d, const node& n)
 template<typename FloatType>
 FloatType float_value(const document_data& d, const node& n, std::true_type /*binary32 or binary64*/)
 {
+#if NLOHMANN_VIEW_VECTOR
+    FloatType value {};
+    if (coordinate_float(d, n, value))
+    {
+        return value;
+    }
+#endif
    const unsigned int_digits = n.extra & 0xFFu;
    const unsigned frac_digits = n.extra >> 8u;
    if (NLOHMANN_VIEW_LIKELY(int_digits + frac_digits <= 19)) // (255 marks "many")
@@ -6368,7 +6513,9 @@ NLOHMANN_JSON_NAMESPACE_END
 #include <cstddef> // size_t
 #include <cstdint> // uint8_t, uint32_t
 #include <cstring> // memcpy, memset
+#include <functional> // less
 #include <limits> // numeric_limits
+#include <memory> // unique_ptr
 #include <type_traits> // integral_constant
 #include <vector> // vector

@@ -6743,6 +6890,127 @@ struct depth_counter<false>
    }
 };

+/*!
+@brief where the double x nearest to a token w * 10^q lies, for 10^15 <= w <
+10^17 and -17 <= q <= -1 (Eisel-Lemire, then a fixed-point position)
+
+dump() writes the shortest decimal in the rounding interval of x (the closest
+one if there are several, see zmij::to_shortest()). Its digits are those of a
+multiple of 10^g of the token's last digit, with g = dec_exp + 1 - q for x's
+decimal exponent dec_exp: the multiple of 10^g nearest to x if it lies in the
+interval (at most one does), else the multiple of 10^(g - 1) nearest to x
+(see token_digits_1() and token_digits_2()). For g <= 0, the token itself is
+in the interval.
+
+The position is exact in a 64-bit fixed-point number with 56 bits after the
+point (of the token's last digit): x / 10^q = 2c * 5^-q / 2^t for x = c * 2^e2
+and t = q + 1 - e2, with at most 56 bits after the point here, and |x / 10^q -
+w| is at most half the spacing of the doubles, below 12 units. So only the low
+64 bits of 2c * 5^-q are needed. c and e2 come from Eisel-Lemire's product
+directly (as eisel_lemire() rounds it: no tie is possible for q < -4, and its
+second product is added where it can carry into the result).
+
+@param[out] offset  x / 10^q - w + 32, with 56 bits after the point
+@param[out] radius  half the spacing of the doubles at x, likewise (+ 1 if
+                    the interval is closed)
+@return g; 3 if the digits are not decided here (a power of two, whose
+        interval is not symmetric, or out of range)
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE int locate_token(std::uint64_t w, int q, std::uint64_t& offset, std::uint64_t& radius) noexcept
+{
+    const int lz = count_leading_zeros(w);
+    const std::uint64_t normalized = w << static_cast<unsigned>(lz);
+    const auto index = static_cast<std::size_t>(2 * (q - pow5_128_smallest_power));
+    const uint128_parts product = full_multiplication(normalized, pow5_128()[index]);
+    std::uint64_t high = product.high;
+    if (NLOHMANN_VIEW_UNLIKELY((high & 0x1FFu) == 0x1FFu))
+    {
+        // (as eisel_lemire(): the lower bits may carry into the result)
+        const std::uint64_t second = full_multiplication(normalized, pow5_128()[index + 1]).high;
+        high += product.low + second < product.low ? 1u : 0u;
+    }
+    const auto upperbit = static_cast<unsigned>(high >> 63u);
+    const std::uint64_t mantissa = high >> (upperbit + 9);
+    const std::uint64_t c = (mantissa + (mantissa & 1u)) >> 1u;
+    // e2 as eisel_lemire() computes the exponent (log2(10) ~ 217706 / 2^16)
+    const int e2 = static_cast<int>((217706 * static_cast<std::int64_t>(q)) >> 16) + 63 + static_cast<int>(upperbit) - lz - 52;
+    const int t = q + 1 - e2;
+    const int g = ((e2 * 315653) >> 20) + 1 - q; // (dec_exp as in zmij::to_shortest(), for a regular x)
+    static const std::array<std::uint64_t, 17> fives = {{1u, 5u, 25u, 125u, 625u, 3125u, 15625u, 78125u, 390625u, 1953125u, 9765625u, 48828125u, 244140625u, 1220703125u, 6103515625u, 30517578125u, 152587890625u}};
+    const std::uint64_t five = fives[static_cast<std::size_t>(-q)]; // 5^-q
+    const unsigned s = static_cast<unsigned>(56 - t) & 63u;
+    offset = ((2 * c * five) << s) - (w << 56u) + (std::uint64_t{32} << 56u);
+    radius = (five << s) + ((c & 1u) == 0 ? 1u : 0u);
+    // (c = 2^52: a power of two; c = 2^53: rounded up to one. With 8 to 16
+    // fraction digits, as the batch's tokens have, t is in [15, 40] and g at
+    // most 2. x lies halfway between two candidates only if its distance from
+    // the token is a whole unit (g == 2) or a half (g == 1): such tokens are
+    // left to the full conversion)
+    const bool decided = c - ((std::uint64_t{1} << 52u) + 1) < (std::uint64_t{1} << 52u) - 1
+                         && (offset & ((std::uint64_t{1} << 55u) - 1)) != 0;
+    return decided ? g : 3;
+}
+
+/// the distance of a position (see locate_token()) from the biased point 32
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t biased_distance(std::uint64_t position) noexcept
+{
+    constexpr std::uint64_t center = std::uint64_t{32} << 56u;
+    return position >= center ? position - center : center - position;
+}
+
+/*!
+@brief (g == 1) the digits dump() writes for a token, from the position of its
+double (see locate_token()): the multiple of 10 nearest to x if it is in the
+interval, else w rounded to x (an exact tie between two candidates, like
+754570942.33984373, whose double is 754570942.33984375, is excluded by
+locate_token())
+
+With |x - w| at most the radius, which is below half the spacing of the
+candidates, the multiple of 10 nearest to x is w - r10 or the one above it.
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_1(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r10 * one); // x - (w - r10) (+ 32)
+    const bool up = from > 37 * one;                  // (nearer to the multiple above)
+    const bool shorter = biased_distance(from - (up ? 10 * one : 0)) < radius;
+    const std::uint64_t a = w - r10 + (up ? 10u : 0u);
+    const std::uint64_t b = w + ((offset + (one / 2)) >> 56u) - 32;                // w rounded to x
+    return shorter ? a : b;
+}
+
+/*!
+@brief (g == 2) the digits dump() writes for a token, as token_digits_1(): the
+multiple of 100 nearest to x if it is in the interval, else the multiple of 10
+nearest to x
+*/
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint64_t token_digits_2(std::uint64_t w, std::uint64_t offset, std::uint64_t radius, std::uint64_t r10, std::uint64_t r100) noexcept
+{
+    constexpr std::uint64_t one = std::uint64_t{1} << 56u;
+    const std::uint64_t from = offset + (r100 * one);
+    const bool up = from > 82 * one;
+    const bool shorter = biased_distance(from - (up ? 100 * one : 0)) < radius;
+    const std::uint64_t a = w - r100 + (up ? 100u : 0u);
+    // x - (w - r10), in [-12, 21]: the multiple of 10 nearest to x is that one,
+    // or one or two above, or one below
+    const std::uint64_t y = offset + (r10 * one);
+    const std::uint64_t steps = (y > 37 * one ? 1u : 0u) + (y > 47 * one ? 1u : 0u);
+    const bool down = y < 27 * one;
+    const std::uint64_t b = w - r10 + (10 * steps) - (down ? 10u : 0u);
+    return shorter ? a : b;
+}
+
+/// the four ASCII digits of x < 10^4, the first in the lowest byte (as
+/// little-endian memory holds them)
+NLOHMANN_VIEW_ALWAYS_INLINE std::uint32_t four_digit_text(std::uint32_t x) noexcept
+{
+    const std::uint32_t ab = (x * 5243u) >> 19u; // x / 100
+    std::uint32_t v = ab | ((x - (ab * 100u)) << 16u);
+    const std::uint32_t a = ((v * 103u) >> 10u) & 0x000F000Fu; // / 10 per 16-bit lane
+    v = a | ((v - (a * 10u)) << 8u);
+    return v + 0x30303030u;
+}
+
 /// how the view's dump() writes a value
 struct dump_style
 {
@@ -7070,6 +7338,7 @@ class view_serializer
        std::array<frame, 32> buffer; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
        std::vector<frame> heap;
        small_stack<frame> stack(buffer.data(), buffer.size(), heap);
+        float_batch batch;
        const char* const src = m_doc.src;
        const char* const src_end = src + m_doc.size;
        char* w = m_out.cursor();
@@ -7209,7 +7478,7 @@ class view_serializer
                    else if (enabled(fast_double::value))
                    {
                        room(64);
-                        w = write_double_at(w, *n);
+                        w = write_double_ahead(w, src, n, batch);
                    }
                    else
                    {
@@ -7234,6 +7503,20 @@ class view_serializer
                case value_t::array:
                {
                    const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
+                    // (read-only documents, compact output) a pair of floats,
+                    // like the coordinates of GeoJSON, without a frame
+                    if (enabled(!Editable && !Pretty && !SourceNumbers && fast_double::value) && n->next == 3 && n->len == 2
+                            && n[1].kind == static_cast<std::uint8_t>(value_t::number_float) && n[2].kind == static_cast<std::uint8_t>(value_t::number_float))
+                    {
+                        room(2 * 64);
+                        *w++ = '[';
+                        w = write_double_ahead(w, src, n + 1, batch);
+                        *w++ = ',';
+                        w = write_double_ahead(w, src, n + 2, batch);
+                        *w++ = ']';
+                        n += 2; // (the element before the next node)
+                        break;
+                    }
                    room(8);
                    if (n->len == 0)
                    {
@@ -7343,6 +7626,247 @@ class view_serializer
        }
    }

+    /// (float_batch) the mark of digits whose rounding carried beyond the
+    /// token's last four (see mark())
+    static constexpr std::uint64_t carried() noexcept
+    {
+        return std::uint64_t{1} << 63u;
+    }
+
+    /// floats of 16 or 17 digits ahead of the walk, converted together (see
+    /// convert_ahead()), with their digits as mark() keeps them
+    struct float_batch
+    {
+        static constexpr std::size_t capacity() noexcept
+        {
+            return 256;
+        }
+        /// (on the heap, allocated by the first conversion: a frame of more
+        /// than a page made every dump of a small document slower)
+        struct entries
+        {
+            std::array<const node*, 256> at; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+            std::array<std::uint64_t, 256> digits; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        };
+        std::unique_ptr<entries> storage{};
+        const node** at = nullptr;
+        std::uint64_t* digits = nullptr;
+        std::size_t count = 0;
+        std::size_t next = 0;
+        const node* scanned = nullptr; ///< where the last scan of the node array ended
+    };
+
+    /// (doubles) the float at n as dump() writes it, at w (64 bytes of room):
+    /// from the batch if it holds n
+    NLOHMANN_VIEW_ALWAYS_INLINE char* write_double_ahead(char* w, const char* src, const node* n, float_batch& batch)
+    {
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+        // (digits 0: not written by the batch; carried(): rounding carried
+        // beyond the last four digits)
+        if (batch.next != batch.count && batch.at[batch.next] == n && batch.digits[batch.next] - 1 < carried() - 1)
+        {
+            return write_token_digits(w, src, *n, batch.digits[batch.next++]);
+        }
+        return write_double_beside(w, n, batch);
+#else
+        static_cast<void>(src);
+        static_cast<void>(batch);
+        return write_double_at(w, *n);
+#endif
+    }
+
+#if NLOHMANN_VIEW_VECTOR && NLOHMANN_VIEW_LITTLE_ENDIAN
+    /// write_double_ahead() for a float that is not the batch's next one (out
+    /// of line: the walk is faster with less code in its loop)
+    NLOHMANN_VIEW_NOINLINE char* write_double_beside(char* w, const node* n, float_batch& batch)
+    {
+        // (an editable document's walk can skip nodes of the array)
+        const std::less<const node*> before;
+        while (batch.next != batch.count && before(batch.at[batch.next], n))
+        {
+            ++batch.next;
+        }
+        if ((batch.next != batch.count && batch.at[batch.next] == n) || convert_ahead(n, batch))
+        {
+            const std::uint64_t digits = batch.digits[batch.next++];
+            if ((digits & carried()) != 0)
+            {
+                return write_carried_digits(w, *n, digits & ~carried());
+            }
+            if (digits != 0)
+            {
+                return write_token_digits(w, m_doc.src, *n, digits);
+            }
+        }
+        return write_double_at(w, *n);
+    }
+
+    /*!
+    @brief convert the floats of 16 or 17 digits among the next nodes of the
+    array at once; whether n is the first of them
+
+    Such tokens (like the coordinates of GeoJSON, written with 17 digits) are
+    written as the token with its last four digits replaced
+    (write_token_digits()). Each step (the digits, locate_token(),
+    token_digits_1/2()) is a long chain of dependent operations; one loop per
+    step over many floats lets the processor overlap the floats, which it does
+    not across the steps of one float (on Apple M1, one loop for the digits and
+    locate_token() made the dump of canada.json 12 % slower). Each node of the array
+    is scanned once; a node that the walk does not reach in order (in an
+    editable document) is written without the batch.
+    */
+    NLOHMANN_VIEW_NOINLINE bool convert_ahead(const node* n, float_batch& batch)
+    {
+        const std::less<const node*> before;
+        const node* const last = m_doc.nodes + m_doc.node_count;
+        if (before(n, batch.scanned) || before(n, m_doc.nodes) || !before(n, last))
+        {
+            return false;
+        }
+        const char* const src = m_doc.src;
+        const char* const src_end = src + m_doc.size;
+        const node* const stop = last - n > 1024 ? n + 1024 : last;
+        batch.count = 0;
+        batch.next = 0;
+        // the digits of each token (and its last four from the text)
+        std::array<std::uint64_t, 256> digits;     // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<int, 256> exponent;             // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint32_t, 256> last_four;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        const node* p = n;
+        if (!batch.storage)
+        {
+            batch.storage.reset(new typename float_batch::entries); // NOLINT(cppcoreguidelines-owning-memory,modernize-make-unique): C++11
+            batch.at = batch.storage->at.data();
+            batch.digits = batch.storage->digits.data();
+        }
+        for (; p != stop && batch.count != float_batch::capacity(); ++p)
+        {
+            // a token of the source: 16 or 17 digits, at least 8 after the
+            // point, no exponent, 32 bytes to read
+            const unsigned frac_digits = p->extra >> 8u;
+            const unsigned int_digits = p->extra & 0xFFu;
+            const unsigned count = int_digits + frac_digits;
+            if (p->kind == static_cast<std::uint8_t>(value_t::number_float) && (p->flags & node_flags::storage) == 0
+                    && count - 16u <= 1u && frac_digits >= 8 && src_end - (src + p->off) >= 33)
+            {
+                const auto* const token = reinterpret_cast<const unsigned char*>(src + p->off); // NOLINT(cppcoreguidelines-pro-type-reinterpret-cast)
+                const unsigned sign = token[0] == '-' ? 1 : 0;
+                const unsigned char* const first = token + sign;
+                const std::uint64_t w = sixteen_digits(first, int_digits);
+                // (the 17th digit follows the point; a token with an exponent
+                // gets digits outside the range of locate_token(), and is not
+                // written by the batch. A token 0.xxx with 16 significant
+                // digits is: its double is written as "0." and its digits too)
+                const std::uint64_t w17 = (w * 10) + static_cast<std::uint64_t>(first[17] - '0');
+                const std::size_t i = batch.count++;
+                batch.at[i] = p;
+                digits[i] = p->len != sign + count + 1 ? 0 : (count == 17 ? w17 : w);
+                exponent[i] = -static_cast<int>(frac_digits);
+                // (byte 0: the last digit, byte 1: the last two, bits 16-29: the last four)
+                std::uint32_t four = 0;
+                std::memcpy(&four, token + p->len - 4, 4);
+                four -= 0x30303030u;
+                const std::uint32_t pairs = ((four & 0x0F0F0F0Fu) * 2561u) >> 8u; // (byte 0, 2: the pairs)
+                last_four[i] = (four >> 24u) | ((pairs >> 16u & 0xFFu) << 8u) | ((((pairs & 0x00FF00FFu) * 6553601u) >> 16u) << 16u);
+            }
+        }
+        batch.scanned = p;
+        // the position of each double, and the floats of either kind
+        std::array<std::uint64_t, 256> offset; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint64_t, 256> radius; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_1;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::array<std::uint8_t, 256> kind_2;  // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
+        std::size_t count_1 = 0;
+        std::size_t count_2 = 0;
+        for (std::size_t i = 0; i != batch.count; ++i)
+        {
+            const std::uint64_t w = digits[i];
+            // (the range excludes the values of bytes that are not digits, only
+            // in a damaged image loaded with image_check::bounds)
+            const int g = w - 1000000000000000u < 99000000000000000u ? locate_token(w, exponent[i], offset[i], radius[i]) : 3;
+            batch.digits[i] = g <= 0 ? (last_four[i] >> 16u) + 1 : 0;
+            kind_1[count_1] = static_cast<std::uint8_t>(i);
+            count_1 += g == 1 ? 1 : 0;
+            kind_2[count_2] = static_cast<std::uint8_t>(i);
+            count_2 += g == 2 ? 1 : 0;
+        }
+        // the digits to write, in one loop per kind (see mark())
+        for (std::size_t k = 0; k != count_1; ++k)
+        {
+            const std::size_t i = kind_1[k];
+            const std::uint64_t s = token_digits_1(digits[i], offset[i], radius[i], last_four[i] & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        for (std::size_t k = 0; k != count_2; ++k)
+        {
+            const std::size_t i = kind_2[k];
+            const std::uint64_t s = token_digits_2(digits[i], offset[i], radius[i], last_four[i] & 0xFFu, (last_four[i] >> 8u) & 0xFFu);
+            batch.digits[i] = mark(digits[i], s, last_four[i] >> 16u);
+        }
+        return batch.count != 0 && batch.at[0] == n;
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room), from the digits of its double (see locate_token()) whose
+    rounding carried beyond the token's last four digits
+
+    (like 43.42027299999999 -> 43.420273): the digits go to the writer of
+    Zmij's results as its 15 or 16 leading digits and one more, which omits
+    the trailing zeros.
+    */
+    NLOHMANN_VIEW_NOINLINE char* write_carried_digits(char* w, const node& n, std::uint64_t digits) const noexcept
+    {
+        const int exponent = -(n.extra >> 8u);
+        const std::uint64_t leading = digits / 10;
+        const auto last = static_cast<unsigned char>(digits - (leading * 10));
+        const bool seventeen = digits >= 10000000000000000u;
+        *w = '-';
+        w += m_doc.src[n.off] == '-' ? 1 : 0;
+        return ::nlohmann::detail::dtoa_impl::write_shortest(w, seventeen ? ::nlohmann::detail::zmij::shortest_decimal{leading, exponent, last, last != 0}
+                : ::nlohmann::detail::zmij::shortest_decimal{digits, exponent - 1, 0, false});
+    }
+
+    /// the digits s of a token with the digits w and the last four digits
+    /// r4, as the batch keeps them: the new last four digits + 1 (only those
+    /// are written over the token's), or s marked if it differs from w beyond
+    /// them (0 stays for a float the batch does not write)
+    static std::uint64_t mark(std::uint64_t w, std::uint64_t s, std::uint64_t r4) noexcept
+    {
+        const std::uint64_t last = s - (w - r4);
+        return last < 10000 ? last + 1 : s | carried();
+    }
+
+    /*!
+    @brief a float token of 16 or 17 digits as dump() writes it, at w (64 bytes
+    of room): the token with its last four digits replaced by digits - 1 (see
+    mark(); the others are the token's), and without trailing zeros after the
+    point, but one
+    */
+    char* write_token_digits(char* w, const char* src, const node& n, std::uint64_t digits)
+    {
+        const char* const token = src + n.off;
+        std::memcpy(w, token, 32);
+        char* const end = w + n.len;
+        const std::uint32_t last = four_digit_text(static_cast<std::uint32_t>(digits - 1));
+        std::memcpy(end - 4, &last, 4);
+        // (the token's text before the new digits, from the source: reading
+        // the output back would wait for the stores)
+        std::uint64_t before = 0;
+        std::memcpy(&before, token + n.len - 12, 8);
+        const std::uint32_t last_zeros = last ^ 0x30303030u;
+        const std::uint64_t before_zeros = before ^ 0x3030303030303030u;
+        if (NLOHMANN_VIEW_UNLIKELY(last_zeros == 0 && before_zeros == 0))
+        {
+            return write_double_at(w, n); // (twelve or more trailing zeros)
+        }
+        const unsigned zeros = last_zeros != 0 ? static_cast<unsigned>(count_leading_zeros(last_zeros)) / 8 - 4
+                               : 4 + (static_cast<unsigned>(count_leading_zeros(before_zeros)) / 8);
+        const unsigned frac_digits = n.extra >> 8u;
+        return end - (zeros < frac_digits ? zeros : frac_digits - 1);
+    }
+#endif
+
    /// a float node as dump() writes it
    void write_float_node(const node& n)
    {
@@ -666,61 +666,6 @@ TEST_CASE("json_view")
        CHECK(small.root().materialize() == json::parse("[1,[2,3],{\"a\":\"b\\n\"}]"));
    }

-    SECTION("block sizes")
-    {
-        // documents whose node estimate lies around the size that is allocated
-        // with the header, and whose decoded strings need the first growth of
-        // the buffer, in all sizes around the points where the policies change
-        for (const int count :
-                {
-                    1, 2, 10, 50, 100, 255, 256, 257, 500, 1000, 1023, 1024, 1025, 2000, 5000
-                })
-        {
-            // strings with escapes (decoded text, minified)
-            std::string escaped = "[";
-            for (int i = 0; i < count; ++i)
-            {
-                escaped += (i != 0 ? ",\"a\\n" : "\"a\\n") + std::to_string(i) + "\\u00e4\"";
-            }
-            escaped += ']';
-            json_document e = json_document::parse(escaped);
-            CHECK(e.root().materialize() == json::parse(escaped));
-            e.shrink_to_fit();
-            CHECK(e.root().materialize() == json::parse(escaped));
-
-            // dense numbers (more nodes per byte than the estimate expects)
-            std::string dense = "[";
-            for (int i = 0; i < count; ++i)
-            {
-                dense += (i != 0 ? ",1" : "1");
-            }
-            dense += ']';
-            json_document n = json_document::parse(dense);
-            CHECK(n.node_count() == static_cast<std::size_t>(count) + 1);
-            CHECK(n.root().materialize() == json::parse(dense));
-            n.shrink_to_fit();
-            CHECK(n.root().size() == static_cast<std::size_t>(count));
-
-            // the same documents, pretty-printed
-            const std::string pretty = json::parse(escaped).dump(2);
-            json_document p = json_document::parse(pretty);
-            CHECK(p.root().materialize() == json::parse(escaped));
-        }
-
-        // a large document with a single escape does not need a buffer of the
-        // size of its input
-        std::string large = "[\"a\\n\"";
-        for (int i = 0; i < 100000; ++i)
-        {
-            large += ",1";
-        }
-        large += ']';
-        const json_document l = json_document::parse(large);
-        CHECK(l.root().size() == 100001);
-        CHECK(l.root()[0].get_string() == "a\n");
-        CHECK(l.root()[100000].get<int>() == 1);
-    }
-
    SECTION("source offsets")
    {
        const std::string text = R"(  {"key": "value", "escaped": "a\nb", "n": 42})";
@@ -35,9 +35,9 @@ using json_view_test::has_duplicate_keys;
 #include <string>
 #include <vector>

-// These tests were split off unit-json_view.cpp, whose object file got too large
-// for the MinGW linker (see json_view_test_helpers.hpp). Like that file, this one
-// is also built with C++17, as it mentions JSON_HAS_CPP_17.
+// These tests were split off unit-json_view.cpp, whose object file got too large for the MinGW
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
+// with C++17, as it mentions JSON_HAS_CPP_17.

 TEST_CASE("json_view dump")
 {
@@ -150,6 +150,71 @@ TEST_CASE("json_view dump")
            CHECK(many_doc.root().dump() == json::parse(many_tokens).dump());
        }

+        // tokens of 16 and 17 digits without an exponent (like GeoJSON
+        // coordinates), which dump() converts in batches: doubles exactly
+        // halfway between two candidates for the shortest digits, random
+        // digits, and digits near a shorter decimal (...99999997,
+        // ...00000003), whose rounding carries; in pairs and among other
+        // values, so that the batches are interrupted; the last token near the
+        // end of the text
+        {
+            std::mt19937_64 tokens(5627); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+            const auto draw = [&tokens](std::size_t n)
+            {
+                const std::uint64_t r = tokens() % n;
+                return static_cast<std::size_t>(r);
+            };
+            std::string coordinates = "[754570942.33984373,257769445.56835938,858106901.94921875,97944964.876953125,"
+                                      "[0.5,1e-7],[1.5,-0.0,2.5],[1E2,12.5,0.1,3.25,4.5,5.75,6.125,7.0,8.5],[],[1.5],[1,2.5],[2.5,\"x\"],[[1.5],2.5],";
+            for (int i = 0; i < 20000; ++i)
+            {
+                const std::size_t length = 16 + draw(2);
+                std::string digits(1, static_cast<char>('1' + draw(9)));
+                const std::size_t kept = draw(3) == 0 ? length : 2 + draw(length - 3);
+                for (std::size_t k = 1; k < kept; ++k)
+                {
+                    digits += static_cast<char>('0' + draw(10));
+                }
+                digits += std::string(length - kept, draw(2) == 0 ? '9' : '0');
+                digits.back() = static_cast<char>('0' + draw(10));
+                const std::size_t point = 1 + draw(9);
+                const std::string token = (draw(2) == 0 ? "-" : "") + digits.substr(0, point) + "." + digits.substr(point);
+                coordinates += (i != 0 ? "," : "") + (draw(8) == 0 ? "{\"x\":" + token + ",\"s\":\"a\"}" : "[" + token + "," + token + "]");
+            }
+            coordinates += ",-65.613616999999977]";
+            const json_document parsed = json_document::parse(coordinates);
+            const ordered_json j = ordered_json::parse(coordinates);
+            CHECK(parsed.root().dump() == j.dump());
+            CHECK(parsed.root().dump(1) == j.dump(1));
+            CHECK(parsed.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+            CHECK(parsed.root().back().get<double>() == j.back().get<double>());
+            CHECK(parsed.root().back().dump() == "-65.61361699999998");
+            std::size_t i = 0;
+            for (const json_view v : parsed.root())
+            {
+                const ordered_json& e = j[i++];
+                CHECK(v.dump() == e.dump());
+                if (v.is_array() && v.size() != 0 && v[0].is_number())
+                {
+                    CHECK(v[0].get<double>() == e[0].get<double>());
+                }
+            }
+
+            // an editable document: edits move some arrays, so that the walk
+            // leaves the order of the parsed nodes
+            ordered_json_editable_document editable = ordered_json_editable_document::parse(coordinates);
+            ordered_json expected = j;
+            for (std::size_t k = 0; k < 20000; k += 97)
+            {
+                if (expected[k].is_array())
+                {
+                    editable.push_back(editable.root()[k], ordered_json(1.5));
+                    expected[k].push_back(1.5);
+                }
+            }
+            CHECK(editable.root().dump() == expected.dump());
+        }
+
        // random doubles, written as parse() and dump() would
        std::mt19937_64 rng(1170); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
        std::string many = "[";
@@ -171,768 +236,4 @@ TEST_CASE("json_view dump")
        const nlohmann::basic_json_document<json_float> float_document = nlohmann::basic_json_document<json_float>::parse("[0.1, 1.5e10, 3.4028235e38]");
        CHECK(float_document.root().dump() == json_float::parse("[0.1, 1.5e10, 3.4028235e38]").dump());
    }
-
-    SECTION("members in document order, all of them")
-    {
-        const json_document d = json_document::parse(R"({"b": 1, "a": 2, "b": 3})");
-        CHECK(d.root().dump() == R"({"b":1,"a":2,"b":3})");
-        CHECK(d.root().dump(1) == "{\n \"b\": 1,\n \"a\": 2,\n \"b\": 3\n}");
-        // dump() writes all members, though the lookup finds the first
-        CHECK(d.root()["b"].dump() == "1");
-    }
-
-    SECTION("deep nesting")
-    {
-        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        const json_document deep_document = json_document::parse(deep);
-        CHECK(deep_document.root().dump() == deep);
-    }
-
-    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
-    {
-        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
-        for (const char* const special :
-                {
-                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
-                })
-        {
-            for (std::size_t length = 0; length <= 40; ++length)
-            {
-                for (std::size_t position = 0; position <= length; ++position)
-                {
-                    std::string content(length, 'a');
-                    content.insert(position, special);
-                    const std::array<std::string, 3> texts =
-                    {
-                        {
-                            "\"" + content + "\"",
-                            "[\"" + content + "\"]",
-                            "{\"" + content + "\":1}",
-                        }
-                    };
-                    for (const std::string& text : texts)
-                    {
-                        CAPTURE(text)
-                        const ordered_json_document d = ordered_json_document::parse(text);
-                        const ordered_json j = ordered_json::parse(text);
-                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
-                        CHECK(d.root().dump() == j.dump());
-                    }
-                }
-            }
-        }
-    }
-
-    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
-    {
-        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
-        std::string text = "[";
-        std::size_t in_chunk = 0;
-        const auto append = [&](std::uint32_t cp)
-        {
-            if (cp < 0x80)
-            {
-                if (cp < 0x20 || cp == '"' || cp == '\\')
-                {
-                    return;
-                }
-                text += static_cast<char>(cp);
-            }
-            else if (cp < 0x800)
-            {
-                text += static_cast<char>(0xC0 | (cp >> 6));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-            else if (cp < 0x10000)
-            {
-                text += static_cast<char>(0xE0 | (cp >> 12));
-                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-            else
-            {
-                text += static_cast<char>(0xF0 | (cp >> 18));
-                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
-                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
-                text += static_cast<char>(0x80 | (cp & 0x3F));
-            }
-        };
-        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
-        {
-            if (cp >= 0xD800 && cp < 0xE000)
-            {
-                continue;
-            }
-            if (in_chunk == 0)
-            {
-                text += text.size() > 1 ? ",\"" : "\"";
-            }
-            append(cp);
-            if (++in_chunk == 37)
-            {
-                text += "\"";
-                in_chunk = 0;
-            }
-        }
-        text += in_chunk != 0 ? "\"]" : "]";
-        const ordered_json_document d = ordered_json_document::parse(text);
-        const ordered_json j = ordered_json::parse(text);
-        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
-        CHECK(d.root().dump() == j.dump());
-        CHECK(d.root().dump(2) == j.dump(2));
-    }
-
-    SECTION("deep nesting, indented")
-    {
-        // indentations of up to and beyond the width of the writer's fixed-size copy
-        for (const int depth :
-                {
-                    1, 5, 20, 70, 300
-                })
-        {
-            std::string text;
-            for (int i = 0; i < depth; ++i)
-            {
-                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
-            }
-            text += "[]";
-            for (int i = depth - 1; i >= 0; --i)
-            {
-                text += i % 2 == 0 ? "]" : "}";
-            }
-            const ordered_json_document d = ordered_json_document::parse(text);
-            const ordered_json j = ordered_json::parse(text);
-            for (const int indent :
-                    {
-                        0, 1, 2, 3, 8
-                    })
-            {
-                CHECK(d.root().dump(indent) == j.dump(indent));
-                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
-            }
-        }
-    }
-
-    SECTION("the output buffer of a small value is small")
-    {
-        // an escaped key after the value: its node lies in the arena, so the
-        // source extent of the value cannot be read from the next node
-        const std::string big(100000, 'a');
-        const std::string text = R"({"small":1,"list":[1,2,3],"k\n":")" + big + R"("})";
-        const json_document d = json_document::parse(text);
-        const auto small = d.root()["small"].dump();
-        CHECK(small == "1");
-        CHECK(small.capacity() < 4096);
-        const auto list = d.root()["list"].dump();
-        CHECK(list == "[1,2,3]");
-        CHECK(list.capacity() < 4096);
-        CHECK(d.root()["list"].dump(2).capacity() < 4096);
-
-        // the whole document and the large value are unaffected
-        CHECK(d.root().dump() == ordered_json::parse(text).dump());
-        CHECK(d.root()["k\n"].dump() == "\"" + big + "\"");
-    }
-
-    SECTION("output that outgrows the estimate")
-    {
-        // ensure_ascii writes six bytes for each two-byte character
-        std::string chars;
-        for (int i = 0; i < 5000; ++i)
-        {
-            chars += "\xC3\xA9";
-        }
-        const json_document d = json_document::parse(R"({"a":")" + chars + R"(","k\n":1})");
-        const json expected = json::parse("\"" + chars + "\"");
-        CHECK(d.root()["a"].dump(-1, ' ', true) == expected.dump(-1, ' ', true));
-        CHECK(d.root()["a"].dump(-1, ' ', true).size() == 2 + (5000 * 6));
-    }
-
-    SECTION("ensure_ascii with strings of the source, decoded strings, and edited strings")
-    {
-        // plain ASCII, non-ASCII, escaped (decoded), and mixed strings, as values and as keys;
-        // the second text has a DEL, which ensure_ascii writes as an escape
-        for (const char* const del :
-                {"", "\x7F"
-                })
-        {
-            const std::string text = std::string("{\"plain\":\"abc\",\"caf\xC3\xA9\":\"\xC3\xA9\xE2\x82\xAC\xF0\x9F\x98\x80\",")
-                                     + "\"esc\\n\\\"\":\"a\\tb\\u00e4\\ud83d\\ude00\",\"del\":\"a" + del + "b\",\"\":\"\"," // NOLINT(modernize-raw-string-literal)
-                                     + "\"list\":[\"x\",\"\xC3\xBC\",\"\\\\\",\"long ASCII string with more than thirty-two bytes in it\","
-                                     + "\"long string with more than thirty-two bytes and one non-ASCII byte \xC3\xB6\"],"
-                                     + "\"n\":[1,2.5,-0,true,null]}";
-            const ordered_json j = ordered_json::parse(text);
-            const ordered_json_document d = ordered_json_document::parse(text);
-            CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-            CHECK(d.root().dump(4, ' ', true) == j.dump(4, ' ', true));
-            CHECK(d.root().dump() == j.dump());
-            CHECK(d.root()["list"].dump(-1, ' ', true) == j["list"].dump(-1, ' ', true));
-            CHECK(d.root()["del"].dump(-1, ' ', true) == j["del"].dump(-1, ' ', true));
-
-            // strings that an edit wrote (the source strings that they replace were plain)
-            ordered_json_editable_document e = ordered_json_editable_document::parse(text);
-            ordered_json k = j;
-            e.set(e.root()["plain"], std::string("\xC3\xA4gypten"));
-            k["plain"] = "\xC3\xA4gypten";
-            e.set(e.root()["list"][0], std::string("ascii after edit"));
-            k["list"][0] = "ascii after edit";
-            e.set(e.root()["list"][1], std::string("\xC3\xA4"));
-            k["list"][1] = "\xC3\xA4";
-            e.set(e.root()["del"], std::string("tab\there"));
-            k["del"] = "tab\there";
-            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
-            CHECK(e.root().dump(2, ' ', true) == k.dump(2, ' ', true));
-            CHECK(e.root().dump() == k.dump());
-
-            // strings that were edited from or to ASCII text
-            e.set(e.root()["list"][2], std::string("\xC3\xA4"));
-            k["list"][2] = "\xC3\xA4";
-            e.set(e.root()["list"][4], std::string("plain again"));
-            k["list"][4] = "plain again";
-            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
-        }
-    }
-
-    SECTION("ensure_ascii with DEL or a non-ASCII character at every position")
-    {
-        // the check whether a string of the source has no byte >= 0x7F reads
-        // eight bytes at a time and then the rest one by one
-        for (std::size_t length = 1; length <= 20; ++length)
-        {
-            for (std::size_t pos = 0; pos < length; ++pos)
-            {
-                for (const char* const c :
-                        {
-                            "\x7F", "\x7E", "\xC3\xA4", "\xC3\xBF" // NOLINT(modernize-raw-string-literal)
-                        })
-                {
-                    const std::string s = std::string(pos, 'a') + c + std::string(length - pos - 1, 'b');
-                    std::string text = "[\"";
-                    text.append(s).append("\",{\"").append(s).append("\":1}]");
-                    const json_document d = json_document::parse(text);
-                    const json j = json::parse(text);
-                    CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
-                    CHECK(d.root().dump(1, ' ', true) == j.dump(1, ' ', true));
-                }
-            }
-        }
-    }
-
-    SECTION("streams and discarded views")
-    {
-        const json_document d = json_document::parse(R"({"a": [1, 2]})");
-        std::ostringstream compact;
-        compact << d.root();
-        CHECK(compact.str() == R"({"a":[1,2]})");
-        std::ostringstream pretty;
-        pretty << std::setw(2) << std::setfill('.') << d.root() << d.root()["a"];
-        CHECK(pretty.str() == "{\n..\"a\": [\n....1,\n....2\n..]\n}[1,2]");
-        CHECK(json_view().dump() == json(json::value_t::discarded).dump());
-    }
-}
-
-TEST_CASE("json_view comparison")
-{
-    SECTION("equality of the values parse() produces")
-    {
-        generator g;
-        std::vector<std::string> texts;
-        for (int i = 0; i < 600; ++i)
-        {
-            std::string text;
-            g.value(text, 0);
-            texts.push_back(text);
-            // the same value written differently: sorted keys, canonical numbers
-            texts.push_back(json::parse(text).dump(1));
-        }
-        for (std::size_t i = 0; i + 2 < texts.size(); ++i)
-        {
-            for (std::size_t k = i; k < i + 3; ++k)
-            {
-                CAPTURE(texts[i])
-                CAPTURE(texts[k])
-                const json_document a = json_document::parse(texts[i]);
-                const json_document b = json_document::parse(texts[k]);
-                const json ja = json::parse(texts[i]);
-                const json jb = json::parse(texts[k]);
-                CHECK((a.root() == b.root()) == (ja == jb));
-                CHECK((a.root() != b.root()) == (ja != jb));
-                CHECK((a.root() == jb) == (ja == jb));
-                CHECK((jb == a.root()) == (ja == jb));
-                CHECK((a.root() != jb) == (ja != jb));
-                CHECK((jb != a.root()) == (ja != jb));
-
-                // ordered_json compares members in order
-                const ordered_json_document oa = ordered_json_document::parse(texts[i]);
-                const ordered_json_document ob = ordered_json_document::parse(texts[k]);
-                const ordered_json oja = ordered_json::parse(texts[i]);
-                const ordered_json ojb = ordered_json::parse(texts[k]);
-                CHECK((oa.root() == ob.root()) == (oja == ojb));
-                CHECK((oa.root() == ojb) == (oja == ojb));
-            }
-        }
-    }
-
-    SECTION("numbers, duplicate keys, member order")
-    {
-        const auto same = [](const char* x, const char* y)
-        {
-            const json_document dx = json_document::parse(x);
-            const json_document dy = json_document::parse(y);
-            return dx.root() == dy.root();
-        };
-        CHECK(same("1", "1.0"));
-        CHECK(same("[1, -1, 2.5]", "[1.0, -1.0, 25e-1]"));
-        CHECK(!same("1", "1.5"));
-        CHECK(same("18446744073709551615", "18446744073709551615"));
-        CHECK(same(R"({"a": 1, "a": 2})", R"({"a": 2})"));
-        CHECK(!same(R"({"a": 1, "a": 2})", R"({"a": 1})"));
-        CHECK(same(R"({"a": 1, "b": 2})", R"({"b": 2, "a": 1})"));
-        CHECK(!same(R"({"a": 1})", R"({"a": 1, "b": 2})"));
-        CHECK(!same("[1, 2]", "[2, 1]"));
-        CHECK(!same("\"a\"", "\"b\""));
-        CHECK(same("\"\\u00e9\"", "\"\xc3\xa9\""));
-        CHECK(!same("null", "false"));
-        CHECK(!same("[]", "{}"));
-        const ordered_json_document dup = ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})");
-        const ordered_json_document last = ordered_json_document::parse(R"({"a": 3, "b": 2})");
-        CHECK(dup.root() == last.root());
-        // (== compares as parse() resolves duplicates, a lookup finds the first)
-        CHECK(dup.root()["a"].materialize() == 1);
-        CHECK(dup.root()["a"] != last.root()["a"]);
-        const ordered_json_document ab = ordered_json_document::parse(R"({"a": 1, "b": 2})");
-        const ordered_json_document ba = ordered_json_document::parse(R"({"b": 2, "a": 1})");
-        CHECK(ab.root() != ba.root());
-
-        // discarded values compare as basic_json's do
-        const json discarded(json::value_t::discarded);
-        CHECK((json_view() == json_view()) == (discarded == discarded)); // NOLINT(readability-container-size-empty): operator== is tested
-        CHECK((json_view() == discarded) == (discarded == discarded)); // NOLINT(readability-container-size-empty)
-        const json_document null_document = json_document::parse("null");
-        CHECK(!(json_view() == null_document.root())); // NOLINT(readability-container-size-empty)
-        CHECK(!(null_document.root() == discarded));
-    }
-
-    SECTION("deep nesting")
-    {
-        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
-        const json_document a = json_document::parse(deep);
-        const json_document b = json_document::parse(deep);
-        CHECK(a.root() == b.root());
-        CHECK(a.root() == json::parse(deep));
-        const std::string other = std::string(100000, '[') + "1" + std::string(100000, ']');
-        const json_document c = json_document::parse(other);
-        CHECK(a.root() != c.root());
-    }
-}
-
-TEST_CASE("json_view large objects")
-{
-    // objects with 128 members or more are looked up with a hash index
-    for (const std::size_t members :
-            {
-                127u, 128u, 129u, 10000u
-            })
-    {
-        CAPTURE(members)
-        std::string text = "{";
-        for (std::size_t i = 0; i < members; ++i)
-        {
-            text += (i != 0 ? ",\"" : "\"") + std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\\n" : "") + "\":" + std::to_string(i);
-        }
-        text += R"(,"":"empty key","k1":"a duplicate of an earlier key"})";
-        const json_document d = json_document::parse(text);
-        const json_view v = d.root();
-        const json j = json::parse(text);
-        for (std::size_t i = 0; i < members; ++i)
-        {
-            const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
-            CHECK(v[key].get<std::size_t>() == i);
-            CHECK(v.contains(key));
-            CHECK(v.find(key).key() == key);
-            CHECK(v.at(key).get<std::size_t>() == i);
-            CHECK(!v.contains(key + "x"));
-        }
-        CHECK(v[""].get_string() == "empty key");
-        CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
-        CHECK(!v.contains("missing"));
-        CHECK_THROWS_WITH_AS(v.at("missing"), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
-        CHECK(v == j);
-        CHECK(v.materialize() == j);
-    }
-
-    SECTION("duplicate keys: the first member wins, with and without a table")
-    {
-        // an object of `total` members: the keys "k0".."k<n-1>" in order, then
-        // three keys repeated twice more (one copy in the middle, one at the
-        // end), and two keys repeated once; the value of a member is its
-        // position, so that the first member of a key can be told apart
-        struct member
-        {
-            std::string key;
-            std::size_t position;
-        };
-        const auto make_members = [](std::size_t total)
-        {
-            std::vector<std::string> keys;
-            for (std::size_t i = 0; i + 8 < total; ++i)
-            {
-                keys.push_back("k" + std::to_string(i));
-            }
-            const std::size_t n = keys.size();
-            const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
-            const std::array<std::size_t, 2> twice = {{5, n / 2}};
-            std::vector<std::string> ordered = keys;
-            for (const std::size_t i : triple)
-            {
-                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
-            }
-            for (const std::size_t i : twice)
-            {
-                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
-            }
-            for (const std::size_t i : triple)
-            {
-                ordered.push_back(keys[i]);
-            }
-            std::vector<member> result;
-            result.reserve(ordered.size());
-            for (std::size_t i = 0; i < ordered.size(); ++i)
-            {
-                result.push_back({ordered[i], i});
-            }
-            return result;
-        };
-
-        // 100 and 127 members: no table; 128 members and more: a table
-        for (const std::size_t total :
-                {
-                    100u, 127u, 128u, 200u, 5000u
-                })
-        {
-            CAPTURE(total)
-            const std::vector<member> members = make_members(total);
-            REQUIRE(members.size() >= total);
-            REQUIRE(members.size() >= 100);
-            std::string text = "{";
-            std::map<std::string, std::size_t> first;
-            std::map<std::string, std::size_t> last;
-            std::map<std::string, std::size_t> occurrences;
-            for (const member& m : members)
-            {
-                text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
-                first.insert({m.key, m.position});
-                last[m.key] = m.position;
-                ++occurrences[m.key];
-            }
-            text += '}';
-            REQUIRE(first.size() < members.size());
-
-            const json_document d = json_document::parse(text);
-            const json_view v = d.root();
-            const json j = json::parse(text);
-            CHECK(v.size() == members.size()); // every occurrence is visited
-            const json m = v.materialize();
-            for (const auto& entry : first)
-            {
-                CAPTURE(entry.first)
-                const std::size_t expected = entry.second;
-                CHECK(v[entry.first].get<std::size_t>() == expected);
-                CHECK(v.at(entry.first).get<std::size_t>() == expected);
-                CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
-                CHECK(v.value(entry.first, std::size_t{0}) == expected);
-                CHECK(v.contains(entry.first));
-                CHECK(v.count(entry.first) == occurrences[entry.first]);
-                const std::string pointer = "/" + entry.first;
-                CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
-                CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
-                CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
-                CHECK(v.contains(json::json_pointer(pointer)));
-                // materialize() and parse() keep the last value instead
-                CHECK(j[entry.first].get<std::size_t>() == last.at(entry.first));
-                CHECK(m[entry.first].get<std::size_t>() == last.at(entry.first));
-            }
-            CHECK(!v.contains("k"));
-            CHECK(v["missing"].is_discarded());
-            CHECK(v.materialize() == j);
-            CHECK(v == j);
-        }
-    }
-
-    SECTION("colliding keys")
-    {
-        // the hash is not seeded, so keys that all land in one place must not
-        // make the table build quadratic: such an object gets no table and is
-        // searched linearly
-        constexpr std::size_t members = 300;
-        constexpr std::size_t table_size = 1024; // the table size for 300 members: the next power of two >= 600
-        std::vector<std::string> colliding;
-        std::vector<std::string> spread;
-        for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
-        {
-            std::string key(8, 'a');
-            std::uint64_t x = counter;
-            for (std::size_t i = 0; i < 8; ++i, x /= 26)
-            {
-                key[i] = static_cast<char>('a' + (x % 26));
-            }
-            const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (table_size - 1)) == 0;
-            if (lands_in_slot_zero && colliding.size() < members)
-            {
-                colliding.push_back(key);
-            }
-            else if (!lands_in_slot_zero && spread.size() < members)
-            {
-                spread.push_back(key);
-            }
-        }
-
-        const auto make_text = [](const std::vector<std::string>& keys)
-        {
-            std::string text = "{";
-            for (std::size_t i = 0; i < keys.size(); ++i)
-            {
-                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
-            }
-            return text + "}";
-        };
-        const std::string colliding_text = make_text(colliding);
-        const std::string spread_text = make_text(spread);
-
-        json_document with_collisions = json_document::parse(colliding_text);
-        json_document without_collisions = json_document::parse(spread_text);
-        for (const auto* pair :
-                {
-                    &colliding, &spread
-                })
-        {
-            const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
-            for (std::size_t i = 0; i < members; ++i)
-            {
-                CAPTURE(i)
-                CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
-                CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
-                CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
-                CHECK(!v.contains((*pair)[i] + "x"));
-            }
-            CHECK(!v.contains("missing"));
-        }
-        CHECK(with_collisions.root() == json::parse(colliding_text));
-
-        // only the object with the spread keys got a table (both texts have the
-        // same length, so the tables are the only difference)
-        with_collisions.shrink_to_fit();
-        without_collisions.shrink_to_fit();
-        CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
-    }
-
-    SECTION("keys that differ in their last bytes are spread over the table")
-    {
-        // The hash must spread the usual families of keys (numbered names, hex
-        // strings, dates, short names): a key farther than index_max_displacement
-        // from its home slot would leave the object without a table. The keys
-        // are placed with linear probing, as the table does.
-        const auto max_displacement = [](const std::vector<std::string>& keys)
-        {
-            std::size_t slots = 16;
-            while (slots < 2 * keys.size())
-            {
-                slots *= 2;
-            }
-            std::vector<bool> used(slots, false);
-            std::size_t farthest = 0;
-            for (const std::string& key : keys)
-            {
-                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
-                std::size_t distance = 0;
-                while (used[i])
-                {
-                    i = (i + 1) & (slots - 1);
-                    ++distance;
-                }
-                used[i] = true;
-                farthest = (std::max)(farthest, distance);
-            }
-            return farthest;
-        };
-        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
-        // (a format string that is not a literal is a Flawfinder error)
-        const auto numbered = [](const char* format, int count, int step)
-        {
-            const std::string pattern(format);
-            const std::size_t percent = pattern.find('%');
-            std::size_t conversion = percent + 1;
-            std::size_t width = 0;
-            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
-            {
-                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
-                ++conversion;
-            }
-            const bool hex = pattern[conversion] == 'x';
-            std::vector<std::string> keys;
-            for (int i = 0; i < count; ++i)
-            {
-                std::ostringstream key;
-                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
-                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
-                keys.push_back(key.str());
-            }
-            return keys;
-        };
-        for (const char* format :
-                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
-                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
-                })
-        {
-            CAPTURE(format)
-            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
-            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
-        }
-        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
-        for (const std::size_t length :
-                {
-                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
-                })
-        {
-            CAPTURE(length)
-            std::set<std::string> distinct;
-            // (there are 26 and 676 keys of one and two letters)
-            std::size_t wanted = 700;
-            if (length == 1)
-            {
-                wanted = 26;
-            }
-            else if (length == 2)
-            {
-                wanted = 500;
-            }
-            while (distinct.size() < wanted)
-            {
-                std::string key(length, 'a');
-                for (char& c : key)
-                {
-                    c = static_cast<char>('a' + (rng() % 26));
-                }
-                distinct.insert(key);
-            }
-            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
-        }
-    }
-
-    SECTION("keys of every length that differ in one byte")
-    {
-        // In a large object, a key is found by comparing its bytes with those of the member the
-        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
-        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
-        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
-        std::vector<std::string> keys;
-        std::set<std::string> distinct;
-        for (std::size_t length = 0; length <= 40; ++length)
-        {
-            for (int copy = 0; copy < 5; ++copy)
-            {
-                std::string key(length, 'a');
-                for (char& c : key)
-                {
-                    c = static_cast<char>('a' + (rng() % 26));
-                }
-                if (distinct.insert(key).second)
-                {
-                    keys.push_back(key);
-                }
-            }
-        }
-        std::string text = "{";
-        for (std::size_t i = 0; i < keys.size(); ++i)
-        {
-            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
-        }
-        text += "}";
-        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
-        const json_document d = json_document::parse(text);
-        const json_view v = d.root();
-        for (std::size_t i = 0; i < keys.size(); ++i)
-        {
-            CAPTURE(keys[i])
-            CHECK(v[keys[i]].get<std::size_t>() == i);
-            CHECK(v.at(keys[i]).get<std::size_t>() == i);
-            CHECK(v.contains(keys[i]));
-            for (std::size_t at = 0; at < keys[i].size(); ++at)
-            {
-                std::string other = keys[i];
-                other[at] = other[at] == 'z' ? 'y' : 'z';
-                CAPTURE(other)
-                CHECK(v.contains(other) == (distinct.count(other) != 0));
-            }
-            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
-            if (!keys[i].empty())
-            {
-                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
-            }
-        }
-    }
-
-    SECTION("shrink_to_fit releases the tables' spare capacity")
-    {
-        const auto make_text = [](int objects, int members)
-        {
-            std::string text = "[";
-            for (int object = 0; object < objects; ++object)
-            {
-                text += object != 0 ? ",{" : "{";
-                for (int i = 0, n = members + object; i < n; ++i)
-                {
-                    text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
-                }
-                text += '}';
-            }
-            return text + "]";
-        };
-        const std::string small_text = make_text(5, 150);
-        const std::string big_text = make_text(40, 400);
-
-        // reading a big text, and then a small one, leaves the spare capacity
-        // of the big one: shrink_to_fit() brings the document to the size of
-        // one parsed from the small text alone
-        json_document d = json_document::parse(big_text);
-        const std::size_t big = d.memory_usage();
-        d.read(small_text);
-        CHECK(d.memory_usage() >= big);
-        d.shrink_to_fit();
-        json_document fresh = json_document::parse(small_text);
-        fresh.shrink_to_fit();
-        CHECK(d.memory_usage() == fresh.memory_usage());
-        CHECK(d.memory_usage() < big / 2);
-        CHECK(d.root() == json::parse(small_text));
-        for (int object = 0; object < 5; ++object)
-        {
-            const json_view v = d.root()[static_cast<std::size_t>(object)];
-            for (int i = 0, n = 150 + object; i < n; ++i)
-            {
-                CHECK(v[std::to_string(i)].get<int>() == i);
-            }
-        }
-    }
-
-    SECTION("nested, reused, and in arrays")
-    {
-        std::string inner = "{";
-        for (int i = 0; i < 300; ++i)
-        {
-            inner += (i != 0 ? ",\"m" : "\"m") + std::to_string(i) + "\":" + std::to_string(i);
-        }
-        inner += '}';
-        const std::string text = "[" + inner + ",{\"x\":" + inner + "}," + inner + "]";
-        json_document d = json_document::parse(text);
-        CHECK(d.root()[0]["m299"].get<int>() == 299);
-        CHECK(d.root()[1]["x"]["m150"].get<int>() == 150);
-        CHECK(d.root()[2]["m0"].get<int>() == 0);
-        const std::size_t with_index = d.memory_usage();
-        d.read(std::string("{\"small\": 1}"));
-        CHECK(d.root()["small"].get<int>() == 1);
-        d.read(text);
-        CHECK(d.root()[2]["m7"].get<int>() == 7);
-        CHECK(d.memory_usage() >= with_index / 2);
-    }
 }
@@ -0,0 +1,302 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+using nlohmann::json_document;
+using nlohmann::ordered_json_editable_document;
+using nlohmann::json_view;
+using nlohmann::ordered_json_document;
+using nlohmann::ordered_json_view;
+
+#include "json_view_test_helpers.hpp"
+using json_view_test::generator;
+using json_view_test::has_duplicate_keys;
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iomanip>
+#include <map>
+#include <random>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+// These tests were split off unit-json_view_dump.cpp, whose object file got too large for the MinGW
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
+// with C++17, as it mentions JSON_HAS_CPP_17.
+
+TEST_CASE("json_view dump: escaping, nesting, and output buffers")
+{
+    SECTION("members in document order, all of them")
+    {
+        const json_document d = json_document::parse(R"({"b": 1, "a": 2, "b": 3})");
+        CHECK(d.root().dump() == R"({"b":1,"a":2,"b":3})");
+        CHECK(d.root().dump(1) == "{\n \"b\": 1,\n \"a\": 2,\n \"b\": 3\n}");
+        // dump() writes all members, though the lookup finds the first
+        CHECK(d.root()["b"].dump() == "1");
+    }
+
+    SECTION("deep nesting")
+    {
+        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
+        const json_document deep_document = json_document::parse(deep);
+        CHECK(deep_document.root().dump() == deep);
+    }
+
+    SECTION("ensure_ascii: a character that needs an escape at each position of a string")
+    {
+        // string lengths around the width of the vector steps, in a string value, a key, and a value near the end of the text
+        for (const char* const special :
+                {
+                    "\xC3\xA9", "\xE4\xB8\xAD", "\xF0\x9F\x98\x80", "\x7F", "\\n", "\\u0001", "\\\"", "\\\\"
+                })
+        {
+            for (std::size_t length = 0; length <= 40; ++length)
+            {
+                for (std::size_t position = 0; position <= length; ++position)
+                {
+                    std::string content(length, 'a');
+                    content.insert(position, special);
+                    const std::array<std::string, 3> texts =
+                    {
+                        {
+                            "\"" + content + "\"",
+                            "[\"" + content + "\"]",
+                            "{\"" + content + "\":1}",
+                        }
+                    };
+                    for (const std::string& text : texts)
+                    {
+                        CAPTURE(text)
+                        const ordered_json_document d = ordered_json_document::parse(text);
+                        const ordered_json j = ordered_json::parse(text);
+                        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+                        CHECK(d.root().dump() == j.dump());
+                    }
+                }
+            }
+        }
+    }
+
+    SECTION("ensure_ascii: every character of the Basic Multilingual Plane and some beyond")
+    {
+        // (the two- and three-byte sequences, including the ranges that need a check: E0, ED, EF BF BF)
+        std::string text = "[";
+        std::size_t in_chunk = 0;
+        const auto append = [&](std::uint32_t cp)
+        {
+            if (cp < 0x80)
+            {
+                if (cp < 0x20 || cp == '"' || cp == '\\')
+                {
+                    return;
+                }
+                text += static_cast<char>(cp);
+            }
+            else if (cp < 0x800)
+            {
+                text += static_cast<char>(0xC0 | (cp >> 6));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else if (cp < 0x10000)
+            {
+                text += static_cast<char>(0xE0 | (cp >> 12));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+            else
+            {
+                text += static_cast<char>(0xF0 | (cp >> 18));
+                text += static_cast<char>(0x80 | ((cp >> 12) & 0x3F));
+                text += static_cast<char>(0x80 | ((cp >> 6) & 0x3F));
+                text += static_cast<char>(0x80 | (cp & 0x3F));
+            }
+        };
+        for (std::uint32_t cp = 0x20; cp < 0x10400; ++cp)
+        {
+            if (cp >= 0xD800 && cp < 0xE000)
+            {
+                continue;
+            }
+            if (in_chunk == 0)
+            {
+                text += text.size() > 1 ? ",\"" : "\"";
+            }
+            append(cp);
+            if (++in_chunk == 37)
+            {
+                text += "\"";
+                in_chunk = 0;
+            }
+        }
+        text += in_chunk != 0 ? "\"]" : "]";
+        const ordered_json_document d = ordered_json_document::parse(text);
+        const ordered_json j = ordered_json::parse(text);
+        CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+        CHECK(d.root().dump(2, ' ', true) == j.dump(2, ' ', true));
+        CHECK(d.root().dump() == j.dump());
+        CHECK(d.root().dump(2) == j.dump(2));
+    }
+
+    SECTION("deep nesting, indented")
+    {
+        // indentations of up to and beyond the width of the writer's fixed-size copy
+        for (const int depth :
+                {
+                    1, 5, 20, 70, 300
+                })
+        {
+            std::string text;
+            for (int i = 0; i < depth; ++i)
+            {
+                text += i % 2 == 0 ? "[1," : R"({"k":2,"\u00e9":)";
+            }
+            text += "[]";
+            for (int i = depth - 1; i >= 0; --i)
+            {
+                text += i % 2 == 0 ? "]" : "}";
+            }
+            const ordered_json_document d = ordered_json_document::parse(text);
+            const ordered_json j = ordered_json::parse(text);
+            for (const int indent :
+                    {
+                        0, 1, 2, 3, 8
+                    })
+            {
+                CHECK(d.root().dump(indent) == j.dump(indent));
+                CHECK(d.root().dump(indent, '\t') == j.dump(indent, '\t'));
+            }
+        }
+    }
+
+    SECTION("the output buffer of a small value is small")
+    {
+        // an escaped key after the value: its node lies in the arena, so the
+        // source extent of the value cannot be read from the next node
+        const std::string big(100000, 'a');
+        const std::string text = R"({"small":1,"list":[1,2,3],"k\n":")" + big + R"("})";
+        const json_document d = json_document::parse(text);
+        const auto small = d.root()["small"].dump();
+        CHECK(small == "1");
+        CHECK(small.capacity() < 4096);
+        const auto list = d.root()["list"].dump();
+        CHECK(list == "[1,2,3]");
+        CHECK(list.capacity() < 4096);
+        CHECK(d.root()["list"].dump(2).capacity() < 4096);
+
+        // the whole document and the large value are unaffected
+        CHECK(d.root().dump() == ordered_json::parse(text).dump());
+        CHECK(d.root()["k\n"].dump() == "\"" + big + "\"");
+    }
+
+    SECTION("output that outgrows the estimate")
+    {
+        // ensure_ascii writes six bytes for each two-byte character
+        std::string chars;
+        for (int i = 0; i < 5000; ++i)
+        {
+            chars += "\xC3\xA9";
+        }
+        const json_document d = json_document::parse(R"({"a":")" + chars + R"(","k\n":1})");
+        const json expected = json::parse("\"" + chars + "\"");
+        CHECK(d.root()["a"].dump(-1, ' ', true) == expected.dump(-1, ' ', true));
+        CHECK(d.root()["a"].dump(-1, ' ', true).size() == 2 + (5000 * 6));
+    }
+
+    SECTION("ensure_ascii with strings of the source, decoded strings, and edited strings")
+    {
+        // plain ASCII, non-ASCII, escaped (decoded), and mixed strings, as values and as keys;
+        // the second text has a DEL, which ensure_ascii writes as an escape
+        for (const char* const del :
+                {"", "\x7F"
+                })
+        {
+            const std::string text = std::string("{\"plain\":\"abc\",\"caf\xC3\xA9\":\"\xC3\xA9\xE2\x82\xAC\xF0\x9F\x98\x80\",")
+                                     + "\"esc\\n\\\"\":\"a\\tb\\u00e4\\ud83d\\ude00\",\"del\":\"a" + del + "b\",\"\":\"\"," // NOLINT(modernize-raw-string-literal)
+                                     + "\"list\":[\"x\",\"\xC3\xBC\",\"\\\\\",\"long ASCII string with more than thirty-two bytes in it\","
+                                     + "\"long string with more than thirty-two bytes and one non-ASCII byte \xC3\xB6\"],"
+                                     + "\"n\":[1,2.5,-0,true,null]}";
+            const ordered_json j = ordered_json::parse(text);
+            const ordered_json_document d = ordered_json_document::parse(text);
+            CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+            CHECK(d.root().dump(4, ' ', true) == j.dump(4, ' ', true));
+            CHECK(d.root().dump() == j.dump());
+            CHECK(d.root()["list"].dump(-1, ' ', true) == j["list"].dump(-1, ' ', true));
+            CHECK(d.root()["del"].dump(-1, ' ', true) == j["del"].dump(-1, ' ', true));
+
+            // strings that an edit wrote (the source strings that they replace were plain)
+            ordered_json_editable_document e = ordered_json_editable_document::parse(text);
+            ordered_json k = j;
+            e.set(e.root()["plain"], std::string("\xC3\xA4gypten"));
+            k["plain"] = "\xC3\xA4gypten";
+            e.set(e.root()["list"][0], std::string("ascii after edit"));
+            k["list"][0] = "ascii after edit";
+            e.set(e.root()["list"][1], std::string("\xC3\xA4"));
+            k["list"][1] = "\xC3\xA4";
+            e.set(e.root()["del"], std::string("tab\there"));
+            k["del"] = "tab\there";
+            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
+            CHECK(e.root().dump(2, ' ', true) == k.dump(2, ' ', true));
+            CHECK(e.root().dump() == k.dump());
+
+            // strings that were edited from or to ASCII text
+            e.set(e.root()["list"][2], std::string("\xC3\xA4"));
+            k["list"][2] = "\xC3\xA4";
+            e.set(e.root()["list"][4], std::string("plain again"));
+            k["list"][4] = "plain again";
+            CHECK(e.root().dump(-1, ' ', true) == k.dump(-1, ' ', true));
+        }
+    }
+
+    SECTION("ensure_ascii with DEL or a non-ASCII character at every position")
+    {
+        // the check whether a string of the source has no byte >= 0x7F reads
+        // eight bytes at a time and then the rest one by one
+        for (std::size_t length = 1; length <= 20; ++length)
+        {
+            for (std::size_t pos = 0; pos < length; ++pos)
+            {
+                for (const char* const c :
+                        {
+                            "\x7F", "\x7E", "\xC3\xA4", "\xC3\xBF" // NOLINT(modernize-raw-string-literal)
+                        })
+                {
+                    const std::string s = std::string(pos, 'a') + c + std::string(length - pos - 1, 'b');
+                    std::string text = "[\"";
+                    text.append(s).append("\",{\"").append(s).append("\":1}]");
+                    const json_document d = json_document::parse(text);
+                    const json j = json::parse(text);
+                    CHECK(d.root().dump(-1, ' ', true) == j.dump(-1, ' ', true));
+                    CHECK(d.root().dump(1, ' ', true) == j.dump(1, ' ', true));
+                }
+            }
+        }
+    }
+
+    SECTION("streams and discarded views")
+    {
+        const json_document d = json_document::parse(R"({"a": [1, 2]})");
+        std::ostringstream compact;
+        compact << d.root();
+        CHECK(compact.str() == R"({"a":[1,2]})");
+        std::ostringstream pretty;
+        pretty << std::setw(2) << std::setfill('.') << d.root() << d.root()["a"];
+        CHECK(pretty.str() == "{\n..\"a\": [\n....1,\n....2\n..]\n}[1,2]");
+        CHECK(json_view().dump() == json(json::value_t::discarded).dump());
+    }
+}
@@ -0,0 +1,545 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#include "doctest_compatibility.h"
+
+#include <nlohmann/json_view.hpp>
+using nlohmann::json;
+using nlohmann::ordered_json;
+using nlohmann::json_document;
+using nlohmann::ordered_json_editable_document;
+using nlohmann::json_view;
+using nlohmann::ordered_json_document;
+using nlohmann::ordered_json_view;
+
+#include "json_view_test_helpers.hpp"
+using json_view_test::generator;
+using json_view_test::has_duplicate_keys;
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <cstddef>
+#include <cstdint>
+#include <cstring>
+#include <iomanip>
+#include <map>
+#include <random>
+#include <set>
+#include <sstream>
+#include <string>
+#include <vector>
+
+// These tests were split off unit-json_view_dump.cpp, whose object file got too large for the MinGW
+// linker (see json_view_test_helpers.hpp). Like that file, this one is also built
+// with C++17, as it mentions JSON_HAS_CPP_17.
+
+TEST_CASE("json_view comparison")
+{
+    SECTION("equality of the values parse() produces")
+    {
+        generator g;
+        std::vector<std::string> texts;
+        for (int i = 0; i < 600; ++i)
+        {
+            std::string text;
+            g.value(text, 0);
+            texts.push_back(text);
+            // the same value written differently: sorted keys, canonical numbers
+            texts.push_back(json::parse(text).dump(1));
+        }
+        for (std::size_t i = 0; i + 2 < texts.size(); ++i)
+        {
+            for (std::size_t k = i; k < i + 3; ++k)
+            {
+                CAPTURE(texts[i])
+                CAPTURE(texts[k])
+                const json_document a = json_document::parse(texts[i]);
+                const json_document b = json_document::parse(texts[k]);
+                const json ja = json::parse(texts[i]);
+                const json jb = json::parse(texts[k]);
+                CHECK((a.root() == b.root()) == (ja == jb));
+                CHECK((a.root() != b.root()) == (ja != jb));
+                CHECK((a.root() == jb) == (ja == jb));
+                CHECK((jb == a.root()) == (ja == jb));
+                CHECK((a.root() != jb) == (ja != jb));
+                CHECK((jb != a.root()) == (ja != jb));
+
+                // ordered_json compares members in order
+                const ordered_json_document oa = ordered_json_document::parse(texts[i]);
+                const ordered_json_document ob = ordered_json_document::parse(texts[k]);
+                const ordered_json oja = ordered_json::parse(texts[i]);
+                const ordered_json ojb = ordered_json::parse(texts[k]);
+                CHECK((oa.root() == ob.root()) == (oja == ojb));
+                CHECK((oa.root() == ojb) == (oja == ojb));
+            }
+        }
+    }
+
+    SECTION("numbers, duplicate keys, member order")
+    {
+        const auto same = [](const char* x, const char* y)
+        {
+            const json_document dx = json_document::parse(x);
+            const json_document dy = json_document::parse(y);
+            return dx.root() == dy.root();
+        };
+        CHECK(same("1", "1.0"));
+        CHECK(same("[1, -1, 2.5]", "[1.0, -1.0, 25e-1]"));
+        CHECK(!same("1", "1.5"));
+        CHECK(same("18446744073709551615", "18446744073709551615"));
+        CHECK(same(R"({"a": 1, "a": 2})", R"({"a": 2})"));
+        CHECK(!same(R"({"a": 1, "a": 2})", R"({"a": 1})"));
+        CHECK(same(R"({"a": 1, "b": 2})", R"({"b": 2, "a": 1})"));
+        CHECK(!same(R"({"a": 1})", R"({"a": 1, "b": 2})"));
+        CHECK(!same("[1, 2]", "[2, 1]"));
+        CHECK(!same("\"a\"", "\"b\""));
+        CHECK(same("\"\\u00e9\"", "\"\xc3\xa9\""));
+        CHECK(!same("null", "false"));
+        CHECK(!same("[]", "{}"));
+        const ordered_json_document dup = ordered_json_document::parse(R"({"a": 1, "b": 2, "a": 3})");
+        const ordered_json_document last = ordered_json_document::parse(R"({"a": 3, "b": 2})");
+        CHECK(dup.root() == last.root());
+        // (== compares as parse() resolves duplicates, a lookup finds the first)
+        CHECK(dup.root()["a"].materialize() == 1);
+        CHECK(dup.root()["a"] != last.root()["a"]);
+        const ordered_json_document ab = ordered_json_document::parse(R"({"a": 1, "b": 2})");
+        const ordered_json_document ba = ordered_json_document::parse(R"({"b": 2, "a": 1})");
+        CHECK(ab.root() != ba.root());
+
+        // discarded values compare as basic_json's do
+        const json discarded(json::value_t::discarded);
+        CHECK((json_view() == json_view()) == (discarded == discarded)); // NOLINT(readability-container-size-empty): operator== is tested
+        CHECK((json_view() == discarded) == (discarded == discarded)); // NOLINT(readability-container-size-empty)
+        const json_document null_document = json_document::parse("null");
+        CHECK(!(json_view() == null_document.root())); // NOLINT(readability-container-size-empty)
+        CHECK(!(null_document.root() == discarded));
+    }
+
+    SECTION("deep nesting")
+    {
+        const std::string deep = std::string(100000, '[') + std::string(100000, ']');
+        const json_document a = json_document::parse(deep);
+        const json_document b = json_document::parse(deep);
+        CHECK(a.root() == b.root());
+        CHECK(a.root() == json::parse(deep));
+        const std::string other = std::string(100000, '[') + "1" + std::string(100000, ']');
+        const json_document c = json_document::parse(other);
+        CHECK(a.root() != c.root());
+    }
+}
+
+TEST_CASE("json_view large objects")
+{
+    // objects with 128 members or more are looked up with a hash index
+    for (const std::size_t members :
+            {
+                127u, 128u, 129u, 10000u
+            })
+    {
+        CAPTURE(members)
+        std::string text = "{";
+        for (std::size_t i = 0; i < members; ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\\n" : "") + "\":" + std::to_string(i);
+        }
+        text += R"(,"":"empty key","k1":"a duplicate of an earlier key"})";
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        const json j = json::parse(text);
+        for (std::size_t i = 0; i < members; ++i)
+        {
+            const std::string key = std::string(i % 23, 'k') + std::to_string(i) + (i % 7 == 0 ? "\n" : "");
+            CHECK(v[key].get<std::size_t>() == i);
+            CHECK(v.contains(key));
+            CHECK(v.find(key).key() == key);
+            CHECK(v.at(key).get<std::size_t>() == i);
+            CHECK(!v.contains(key + "x"));
+        }
+        CHECK(v[""].get_string() == "empty key");
+        CHECK(v["k1"].get<int>() == 1); // the first of duplicate keys, as for small objects
+        CHECK(!v.contains("missing"));
+        CHECK_THROWS_WITH_AS(v.at("missing"), "[json.exception.out_of_range.403] key 'missing' not found", json::out_of_range&);
+        CHECK(v == j);
+        CHECK(v.materialize() == j);
+    }
+
+    SECTION("duplicate keys: the first member wins, with and without a table")
+    {
+        // an object of `total` members: the keys "k0".."k<n-1>" in order, then
+        // three keys repeated twice more (one copy in the middle, one at the
+        // end), and two keys repeated once; the value of a member is its
+        // position, so that the first member of a key can be told apart
+        struct member
+        {
+            std::string key;
+            std::size_t position;
+        };
+        const auto make_members = [](std::size_t total)
+        {
+            std::vector<std::string> keys;
+            for (std::size_t i = 0; i + 8 < total; ++i)
+            {
+                keys.push_back("k" + std::to_string(i));
+            }
+            const std::size_t n = keys.size();
+            const std::array<std::size_t, 3> triple = {{3, 17, n - 1}};
+            const std::array<std::size_t, 2> twice = {{5, n / 2}};
+            std::vector<std::string> ordered = keys;
+            for (const std::size_t i : triple)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 2), keys[i]);
+            }
+            for (const std::size_t i : twice)
+            {
+                ordered.insert(ordered.begin() + static_cast<std::ptrdiff_t>(ordered.size() / 3), keys[i]);
+            }
+            for (const std::size_t i : triple)
+            {
+                ordered.push_back(keys[i]);
+            }
+            std::vector<member> result;
+            result.reserve(ordered.size());
+            for (std::size_t i = 0; i < ordered.size(); ++i)
+            {
+                result.push_back({ordered[i], i});
+            }
+            return result;
+        };
+
+        // 100 and 127 members: no table; 128 members and more: a table
+        for (const std::size_t total :
+                {
+                    100u, 127u, 128u, 200u, 5000u
+                })
+        {
+            CAPTURE(total)
+            const std::vector<member> members = make_members(total);
+            REQUIRE(members.size() >= total);
+            REQUIRE(members.size() >= 100);
+            std::string text = "{";
+            std::map<std::string, std::size_t> first;
+            std::map<std::string, std::size_t> last;
+            std::map<std::string, std::size_t> occurrences;
+            for (const member& m : members)
+            {
+                text += (text.size() > 1 ? ",\"" : "\"") + m.key + "\":" + std::to_string(m.position);
+                first.insert({m.key, m.position});
+                last[m.key] = m.position;
+                ++occurrences[m.key];
+            }
+            text += '}';
+            REQUIRE(first.size() < members.size());
+
+            const json_document d = json_document::parse(text);
+            const json_view v = d.root();
+            const json j = json::parse(text);
+            CHECK(v.size() == members.size()); // every occurrence is visited
+            const json m = v.materialize();
+            for (const auto& entry : first)
+            {
+                CAPTURE(entry.first)
+                const std::size_t expected = entry.second;
+                CHECK(v[entry.first].get<std::size_t>() == expected);
+                CHECK(v.at(entry.first).get<std::size_t>() == expected);
+                CHECK(v.find(entry.first).value().get<std::size_t>() == expected);
+                CHECK(v.value(entry.first, std::size_t{0}) == expected);
+                CHECK(v.contains(entry.first));
+                CHECK(v.count(entry.first) == occurrences[entry.first]);
+                const std::string pointer = "/" + entry.first;
+                CHECK(v[json::json_pointer(pointer)].get<std::size_t>() == expected);
+                CHECK(v.at(json::json_pointer(pointer)).get<std::size_t>() == expected);
+                CHECK(v.value(json::json_pointer(pointer), std::size_t{0}) == expected);
+                CHECK(v.contains(json::json_pointer(pointer)));
+                // materialize() and parse() keep the last value instead
+                CHECK(j[entry.first].get<std::size_t>() == last.at(entry.first));
+                CHECK(m[entry.first].get<std::size_t>() == last.at(entry.first));
+            }
+            CHECK(!v.contains("k"));
+            CHECK(v["missing"].is_discarded());
+            CHECK(v.materialize() == j);
+            CHECK(v == j);
+        }
+    }
+
+    SECTION("colliding keys")
+    {
+        // the hash is not seeded, so keys that all land in one place must not
+        // make the table build quadratic: such an object gets no table and is
+        // searched linearly
+        constexpr std::size_t members = 300;
+        constexpr std::size_t table_size = 1024; // the table size for 300 members: the next power of two >= 600
+        std::vector<std::string> colliding;
+        std::vector<std::string> spread;
+        for (std::uint64_t counter = 0; colliding.size() < members || spread.size() < members; ++counter)
+        {
+            std::string key(8, 'a');
+            std::uint64_t x = counter;
+            for (std::size_t i = 0; i < 8; ++i, x /= 26)
+            {
+                key[i] = static_cast<char>('a' + (x % 26));
+            }
+            const bool lands_in_slot_zero = (nlohmann::detail::view::key_hash(key.data(), key.size()) & (table_size - 1)) == 0;
+            if (lands_in_slot_zero && colliding.size() < members)
+            {
+                colliding.push_back(key);
+            }
+            else if (!lands_in_slot_zero && spread.size() < members)
+            {
+                spread.push_back(key);
+            }
+        }
+
+        const auto make_text = [](const std::vector<std::string>& keys)
+        {
+            std::string text = "{";
+            for (std::size_t i = 0; i < keys.size(); ++i)
+            {
+                text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i % 10);
+            }
+            return text + "}";
+        };
+        const std::string colliding_text = make_text(colliding);
+        const std::string spread_text = make_text(spread);
+
+        json_document with_collisions = json_document::parse(colliding_text);
+        json_document without_collisions = json_document::parse(spread_text);
+        for (const auto* pair :
+                {
+                    &colliding, &spread
+                })
+        {
+            const json_view v = (pair == &colliding ? with_collisions : without_collisions).root();
+            for (std::size_t i = 0; i < members; ++i)
+            {
+                CAPTURE(i)
+                CHECK(v[(*pair)[i]].get<std::size_t>() == i % 10);
+                CHECK(v.at((*pair)[i]).get<std::size_t>() == i % 10);
+                CHECK(v.find((*pair)[i]).key() == (*pair)[i]);
+                CHECK(!v.contains((*pair)[i] + "x"));
+            }
+            CHECK(!v.contains("missing"));
+        }
+        CHECK(with_collisions.root() == json::parse(colliding_text));
+
+        // only the object with the spread keys got a table (both texts have the
+        // same length, so the tables are the only difference)
+        with_collisions.shrink_to_fit();
+        without_collisions.shrink_to_fit();
+        CHECK(without_collisions.memory_usage() >= with_collisions.memory_usage() + (table_size * sizeof(std::uint32_t)));
+    }
+
+    SECTION("keys that differ in their last bytes are spread over the table")
+    {
+        // The hash must spread the usual families of keys (numbered names, hex
+        // strings, dates, short names): a key farther than index_max_displacement
+        // from its home slot would leave the object without a table. The keys
+        // are placed with linear probing, as the table does.
+        const auto max_displacement = [](const std::vector<std::string>& keys)
+        {
+            std::size_t slots = 16;
+            while (slots < 2 * keys.size())
+            {
+                slots *= 2;
+            }
+            std::vector<bool> used(slots, false);
+            std::size_t farthest = 0;
+            for (const std::string& key : keys)
+            {
+                std::size_t i = nlohmann::detail::conditional_static_cast<std::size_t>(nlohmann::detail::view::key_hash(key.data(), key.size())) & (slots - 1);
+                std::size_t distance = 0;
+                while (used[i])
+                {
+                    i = (i + 1) & (slots - 1);
+                    ++distance;
+                }
+                used[i] = true;
+                farthest = (std::max)(farthest, distance);
+            }
+            return farthest;
+        };
+        // the keys of a printf-like pattern with one %d, %0Nd or %0Nx, formatted with a stream
+        // (a format string that is not a literal is a Flawfinder error)
+        const auto numbered = [](const char* format, int count, int step)
+        {
+            const std::string pattern(format);
+            const std::size_t percent = pattern.find('%');
+            std::size_t conversion = percent + 1;
+            std::size_t width = 0;
+            while (pattern[conversion] >= '0' && pattern[conversion] <= '9')
+            {
+                width = (width * 10) + static_cast<std::size_t>(pattern[conversion] - '0');
+                ++conversion;
+            }
+            const bool hex = pattern[conversion] == 'x';
+            std::vector<std::string> keys;
+            for (int i = 0; i < count; ++i)
+            {
+                std::ostringstream key;
+                key << pattern.substr(0, percent) << std::setfill('0') << std::setw(static_cast<int>(width))
+                    << (hex ? std::hex : std::dec) << (i * step) << pattern.substr(conversion + 1);
+                keys.push_back(key.str());
+            }
+            return keys;
+        };
+        for (const char* format :
+                {"key%d", "%d", "item_%04d", "a%05d", "%03dxyz", "id%d", "user_%d", "%d_suffix", "0x%04x", "A%07d", "12345678%d", "1234567%d", "123456789%d",
+                 "configuration_parameter_value_%04d_extra", "2026-01-%02dT00:00:00Z"
+                })
+        {
+            CAPTURE(format)
+            CHECK(max_displacement(numbered(format, std::string(format).find("%02d") != std::string::npos ? 60 : 1000, 1)) < nlohmann::detail::view::index_max_displacement); // NOLINT(abseil-string-find-str-contains)
+            CHECK(max_displacement(numbered(format, 600, 7)) < nlohmann::detail::view::index_max_displacement);
+        }
+        std::mt19937_64 rng(7); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        for (const std::size_t length :
+                {
+                    std::size_t{1}, std::size_t{2}, std::size_t{3}, std::size_t{5}, std::size_t{7}, std::size_t{8}, std::size_t{9}, std::size_t{12}, std::size_t{16}, std::size_t{17}, std::size_t{33}
+                })
+        {
+            CAPTURE(length)
+            std::set<std::string> distinct;
+            // (there are 26 and 676 keys of one and two letters)
+            std::size_t wanted = 700;
+            if (length == 1)
+            {
+                wanted = 26;
+            }
+            else if (length == 2)
+            {
+                wanted = 500;
+            }
+            while (distinct.size() < wanted)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                distinct.insert(key);
+            }
+            CHECK(max_displacement(std::vector<std::string>(distinct.begin(), distinct.end())) < nlohmann::detail::view::index_max_displacement);
+        }
+    }
+
+    SECTION("keys of every length that differ in one byte")
+    {
+        // In a large object, a key is found by comparing its bytes with those of the member the
+        // table points to: up to 16 bytes as two overlapping words, longer ones with memcmp.
+        // Keys of every length from 0 to 40, and keys that differ from them in one byte.
+        std::mt19937_64 rng(2026); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed)
+        std::vector<std::string> keys;
+        std::set<std::string> distinct;
+        for (std::size_t length = 0; length <= 40; ++length)
+        {
+            for (int copy = 0; copy < 5; ++copy)
+            {
+                std::string key(length, 'a');
+                for (char& c : key)
+                {
+                    c = static_cast<char>('a' + (rng() % 26));
+                }
+                if (distinct.insert(key).second)
+                {
+                    keys.push_back(key);
+                }
+            }
+        }
+        std::string text = "{";
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            text += (i != 0 ? ",\"" : "\"") + keys[i] + "\":" + std::to_string(i);
+        }
+        text += "}";
+        REQUIRE(keys.size() >= 128); // (a table is built for 128 members)
+        const json_document d = json_document::parse(text);
+        const json_view v = d.root();
+        for (std::size_t i = 0; i < keys.size(); ++i)
+        {
+            CAPTURE(keys[i])
+            CHECK(v[keys[i]].get<std::size_t>() == i);
+            CHECK(v.at(keys[i]).get<std::size_t>() == i);
+            CHECK(v.contains(keys[i]));
+            for (std::size_t at = 0; at < keys[i].size(); ++at)
+            {
+                std::string other = keys[i];
+                other[at] = other[at] == 'z' ? 'y' : 'z';
+                CAPTURE(other)
+                CHECK(v.contains(other) == (distinct.count(other) != 0));
+            }
+            CHECK(v.contains(keys[i] + "a") == (distinct.count(keys[i] + "a") != 0));
+            if (!keys[i].empty())
+            {
+                CHECK(v.contains(keys[i].substr(1)) == (distinct.count(keys[i].substr(1)) != 0));
+            }
+        }
+    }
+
+    SECTION("shrink_to_fit releases the tables' spare capacity")
+    {
+        const auto make_text = [](int objects, int members)
+        {
+            std::string text = "[";
+            for (int object = 0; object < objects; ++object)
+            {
+                text += object != 0 ? ",{" : "{";
+                for (int i = 0, n = members + object; i < n; ++i)
+                {
+                    text += (i != 0 ? ",\"" : "\"") + std::to_string(i) + "\":" + std::to_string(i);
+                }
+                text += '}';
+            }
+            return text + "]";
+        };
+        const std::string small_text = make_text(5, 150);
+        const std::string big_text = make_text(40, 400);
+
+        // reading a big text, and then a small one, leaves the spare capacity
+        // of the big one: shrink_to_fit() brings the document to the size of
+        // one parsed from the small text alone
+        json_document d = json_document::parse(big_text);
+        const std::size_t big = d.memory_usage();
+        d.read(small_text);
+        CHECK(d.memory_usage() >= big);
+        d.shrink_to_fit();
+        json_document fresh = json_document::parse(small_text);
+        fresh.shrink_to_fit();
+        CHECK(d.memory_usage() == fresh.memory_usage());
+        CHECK(d.memory_usage() < big / 2);
+        CHECK(d.root() == json::parse(small_text));
+        for (int object = 0; object < 5; ++object)
+        {
+            const json_view v = d.root()[static_cast<std::size_t>(object)];
+            for (int i = 0, n = 150 + object; i < n; ++i)
+            {
+                CHECK(v[std::to_string(i)].get<int>() == i);
+            }
+        }
+    }
+
+    SECTION("nested, reused, and in arrays")
+    {
+        std::string inner = "{";
+        for (int i = 0; i < 300; ++i)
+        {
+            inner += (i != 0 ? ",\"m" : "\"m") + std::to_string(i) + "\":" + std::to_string(i);
+        }
+        inner += '}';
+        const std::string text = "[" + inner + ",{\"x\":" + inner + "}," + inner + "]";
+        json_document d = json_document::parse(text);
+        CHECK(d.root()[0]["m299"].get<int>() == 299);
+        CHECK(d.root()[1]["x"]["m150"].get<int>() == 150);
+        CHECK(d.root()[2]["m0"].get<int>() == 0);
+        const std::size_t with_index = d.memory_usage();
+        d.read(std::string("{\"small\": 1}"));
+        CHECK(d.root()["small"].get<int>() == 1);
+        d.read(text);
+        CHECK(d.root()[2]["m7"].get<int>() == 7);
+        CHECK(d.memory_usage() >= with_index / 2);
+    }
+}