Write integers of 17 to 20 digits eight digits at a time in dump() (#5964)

#5634 made dump() write integers below 10^16 eight digits at a time; larger
ones still took the two-digits-per-division loop and count_digits(). Random
64-bit integers almost all have 17 to 20 digits (99.9 % of signed_ints.json
and unsigned_ints.json), so Dump/signed_ints and Dump/unsigned_ints gained
only 1.4x over 3.12.0, against 2.3x for small integers.

A 64-bit magnitude is now written as its first one to four digits and two
groups of eight. Wider magnitudes (__int128 and class types, #5805) keep the
loop: number types of at most 64 bits are selected by type, so no comparison
is reported as always true; for others the value is compared. The sign
handling of #1447/#5815 (remove_sign() into number_magnitude_t) is unchanged.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/detail/input/binary_reader.hpp

@@ -4293,19 +4293,6 @@ class binary_reader
         return get_bytes(len, "string", result);
     }
 
-    /// whether @a s is valid UTF-8: ASCII eight bytes at a time, the rest
-    /// sequence by sequence (as the binary writers check strings)
-    static bool is_valid_utf8_string(const string_t& s, std::true_type /*is_byte*/) noexcept
-    {
-        return valid_utf8_string(reinterpret_cast<const unsigned char*>(s.data()), s.size());
-    }
-
-    /// whether @a s, of a character type wider than a byte, is valid UTF-8
-    static bool is_valid_utf8_string(const string_t& s, std::false_type /*is_byte*/) noexcept
-    {
-        return is_valid_utf8(s);
-    }
-
     /*!
     @brief validate a decoded text string (value or object key) against @ref error_handler
 
@@ -4325,16 +4312,7 @@ class binary_reader
     */
     bool check_string_utf8(string_t& result, const char* context)
     {
-        return error_handler == error_handler_t::keep || check_string_utf8_handler(result, context);
+        if (error_handler == error_handler_t::keep || is_valid_utf8(result))
-    }
-
-    /// @ref check_string_utf8 for an error handler other than @ref
-    /// error_handler_t::keep; out of line, so that reading strings without a
-    /// check does not pay for the code of the check
-    JSON_HEDLEY_NEVER_INLINE
-    bool check_string_utf8_handler(string_t& result, const char* context)
-    {
-        if (is_valid_utf8_string(result, std::integral_constant<bool, sizeof(typename string_t::value_type) == 1>()))
         {
             return true;
         }

include/nlohmann/detail/input/simd_scan.hpp

@@ -322,78 +322,6 @@ JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline bool vector_utf8_run(cons
     block_out = block;
     return false;
 }
-
-/*!
-@brief skip 16-byte blocks of well-formed UTF-8 at p (a character boundary)
-
-Like vector_utf8_run, but quotes, backslashes, and control characters are
-ordinary characters. Returns the start of the first block in which the check
-found an error (which may belong to a sequence begun in the block before) or
-where fewer than 16 bytes are left; a sequence may be cut at that point, so the
-caller resumes at its start, one sequence at a time.
-*/
-JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline const unsigned char* vector_utf8_valid_blocks(const unsigned char* block, const unsigned char* e) noexcept
-{
-    using lookup = utf8_lookup4<>;
-#if JSON_SCAN_NEON
-    const uint8x16_t t1h = vld1q_u8(lookup::byte_1_high.data());
-    const uint8x16_t t1l = vld1q_u8(lookup::byte_1_low.data());
-    const uint8x16_t t2h = vld1q_u8(lookup::byte_2_high.data());
-    uint8x16_t prev = vdupq_n_u8(0);
-    while (e - block >= 16)
-    {
-        const uint8x16_t in = vld1q_u8(block);
-        if (vmaxvq_u8(vorrq_u8(in, prev)) < 0x80)
-        {
-            // ASCII here, and no sequence from the block before to finish
-            prev = in;
-            block += 16;
-            continue;
-        }
-        const uint8x16_t prev1 = vextq_u8(prev, in, 15);
-        const uint8x16_t sc = vandq_u8(vandq_u8(vqtbl1q_u8(t1h, vshrq_n_u8(prev1, 4)), vqtbl1q_u8(t1l, vandq_u8(prev1, vdupq_n_u8(0x0F)))), vqtbl1q_u8(t2h, vshrq_n_u8(in, 4)));
-        const uint8x16_t must23 = vorrq_u8(vqsubq_u8(vextq_u8(prev, in, 14), vdupq_n_u8(0xE0 - 0x80)), vqsubq_u8(vextq_u8(prev, in, 13), vdupq_n_u8(0xF0 - 0x80)));
-        const uint8x16_t err = veorq_u8(vandq_u8(must23, vdupq_n_u8(0x80)), sc);
-        if (vmaxvq_u8(err) != 0)
-        {
-            break;
-        }
-        prev = in;
-        block += 16;
-    }
-#else
-    const __m128i t1h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_high.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i t1l = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_low.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i t2h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_2_high.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i nibble = _mm_set1_epi8(0x0F);
-    const __m128i zero = _mm_setzero_si128();
-    __m128i prev = zero;
-    while (e - block >= 16)
-    {
-        const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(block))); // NOLINT(bugprone-casting-through-void)
-        if (_mm_movemask_epi8(_mm_or_si128(in, prev)) == 0)
-        {
-            prev = in;
-            block += 16;
-            continue;
-        }
-        const __m128i prev1 = _mm_alignr_epi8(in, prev, 15);
-        const __m128i sc = _mm_and_si128(_mm_and_si128(_mm_shuffle_epi8(t1h, _mm_and_si128(_mm_srli_epi16(prev1, 4), nibble)),
-                                         _mm_shuffle_epi8(t1l, _mm_and_si128(prev1, nibble))),
-                                         _mm_shuffle_epi8(t2h, _mm_and_si128(_mm_srli_epi16(in, 4), nibble)));
-        const __m128i must23 = _mm_or_si128(_mm_subs_epu8(_mm_alignr_epi8(in, prev, 14), _mm_set1_epi8(0xE0 - 0x80)),
-                                            _mm_subs_epu8(_mm_alignr_epi8(in, prev, 13), _mm_set1_epi8(0xF0 - 0x80)));
-        const __m128i err = _mm_xor_si128(_mm_and_si128(must23, _mm_set1_epi8(static_cast<char>(-128))), sc);
-        if (_mm_movemask_epi8(_mm_cmpeq_epi8(err, zero)) != 0xFFFF)
-        {
-            break;
-        }
-        prev = in;
-        block += 16;
-    }
-#endif
-    return block;
-}
 #endif
 
 }  // namespace detail

include/nlohmann/detail/input/string_scan.hpp

@@ -236,64 +236,6 @@ inline std::size_t valid_utf8_prefix(const unsigned char* data, std::size_t n) n
     return pos;
 }
 
-/*!
-@brief whether [data, data+n) is valid UTF-8, for checking whole strings
-
-The same answer as valid_utf8_prefix(data, n) == n. Short ASCII strings, the
-most common keys and values, are decided in one test, and long strings are
-checked 16 bytes at a time where the vector check is available.
-*/
-inline bool valid_utf8_string(const unsigned char* data, std::size_t n) noexcept
-{
-    constexpr std::uint64_t high = 0x8080808080808080ull;
-    if (n <= 16)
-    {
-        // two overlapping words cover 8 to 16 bytes, one partial word fewer
-        std::uint64_t first = 0;
-        std::uint64_t last = 0;
-        if (n >= 8)
-        {
-            std::memcpy(&first, data, sizeof(first));
-            std::memcpy(&last, data + n - 8, sizeof(last));
-        }
-        else if (n != 0)
-        {
-            std::memcpy(&first, data, n);
-        }
-        if (((first | last) & high) == 0)
-        {
-            return true;
-        }
-    }
-#if JSON_SCAN_VECTOR_UTF8
-    else if (n >= 32
-#if JSON_SCAN_SSSE3_DISPATCH
-             && cpu_has_ssse3()
-#endif
-            )
-    {
-        const unsigned char* block = vector_utf8_valid_blocks(data, data + n);
-        // the rest from the start of a sequence that may be cut at block
-        for (int i = 1; i <= 3 && block - i >= data; ++i)
-        {
-            const unsigned char c = block[-i];
-            if (c < 0x80)
-            {
-                break;
-            }
-            if (c >= 0xC0)
-            {
-                block -= i;
-                break;
-            }
-        }
-        const auto checked = static_cast<std::size_t>(block - data);
-        return checked + valid_utf8_prefix(block, n - checked) == n;
-    }
-#endif
-    return valid_utf8_prefix(data, n) == n;
-}
-
 #if JSON_SCAN_VECTOR_UTF8
 /// the end of scan_string_vector from block, where the vector loop stopped
 /// (ill-formed UTF-8, or fewer than 16 bytes left): one byte or sequence at a

include/nlohmann/detail/output/binary_writer.hpp

@@ -3080,25 +3080,6 @@ class binary_writer
         }
     }
 
-    /// write the head and the characters of @a value, at most
-    /// max_text_in_reservation of them, in one reservation
-    JSON_HEDLEY_ALWAYS_INLINE void write_cbor_string_reserved(const string_t& value)
-    {
-        CharType* const out = oa.reserve(value.size() + 2);
-        CharType* p = out;
-        if (value.size() <= 0x17)
-        {
-            *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
-        }
-        else
-        {
-            *p++ = to_char_type(0x78);
-            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-        }
-        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-        oa.commit(static_cast<std::size_t>(p - out) + value.size());
-    }
-
     /*!
     @brief write a CBOR text string
 
@@ -3120,7 +3101,19 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                write_cbor_string_reserved(value);
+                CharType* const out = oa.reserve(value.size() + 2);
+                CharType* p = out;
+                if (value.size() <= 0x17)
+                {
+                    *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
+                }
+                else
+                {
+                    *p++ = to_char_type(0x78);
+                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+                }
+                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -3134,13 +3127,6 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_cbor_checked_string(const string_t& value, const BasicJsonType& context)
     {
-        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
-        {
-            check_utf8(value, context);
-            write_cbor_string_reserved(value);
-            return;
-        }
-
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -3155,27 +3141,6 @@ class binary_writer
     // MsgPack //
     /////////////
 
-    /// write the head and the characters of @a value, at most
-    /// max_text_in_reservation of them, in one reservation
-    JSON_HEDLEY_ALWAYS_INLINE void write_msgpack_string_reserved(const string_t& value)
-    {
-        CharType* const out = oa.reserve(value.size() + 2);
-        CharType* p = out;
-        if (value.size() <= 31)
-        {
-            // fixstr
-            *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
-        }
-        else
-        {
-            // str 8
-            *p++ = to_char_type(0xD9);
-            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-        }
-        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-        oa.commit(static_cast<std::size_t>(p - out) + value.size());
-    }
-
     /*!
     @brief write a MessagePack str
 
@@ -3193,7 +3158,21 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                write_msgpack_string_reserved(value);
+                CharType* const out = oa.reserve(value.size() + 2);
+                CharType* p = out;
+                if (value.size() <= 31)
+                {
+                    // fixstr
+                    *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
+                }
+                else
+                {
+                    // str 8
+                    *p++ = to_char_type(0xD9);
+                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+                }
+                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -3206,13 +3185,6 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_msgpack_checked_string(const string_t& value, const BasicJsonType& context)
     {
-        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
-        {
-            check_utf8(value, context);
-            write_msgpack_string_reserved(value);
-            return;
-        }
-
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -4822,9 +4794,10 @@ class binary_writer
     static void check_utf8(const string_t& s, const BasicJsonType& context)
     {
         const auto* data = reinterpret_cast<const unsigned char*>(s.data());
-        if (JSON_HEDLEY_UNLIKELY(!valid_utf8_string(data, s.size())))
+        const std::size_t valid = valid_utf8_prefix(data, s.size());
+        if (JSON_HEDLEY_UNLIKELY(valid != s.size()))
         {
-            throw_invalid_utf8(data, valid_utf8_prefix(data, s.size()), context);
+            throw_invalid_utf8(data, valid, context);
         }
     }
 

include/nlohmann/detail/output/serializer.hpp

@@ -1977,6 +1977,23 @@ class serializer
             return;
         }
 
+        // 17 to 20 digits: the first one to four, then twice eight
+        if (magnitude_fits_64_bits(abs_value, std::integral_constant<bool, magnitude_has_at_most_64_bits>()))
+        {
+            const auto value = static_cast<std::uint64_t>(abs_value);
+            const std::uint64_t top = value / 10000000000000000u; // 1 to 1844
+            const std::uint64_t low16 = value - (top * 10000000000000000u);
+            const std::uint64_t middle = low16 / 100000000u;
+            const std::uint64_t first = dtoa_impl::eight_digit_bytes(top);
+            const auto leading = static_cast<unsigned>(count_leading_zeros(first) / 8); // (first is not 0)
+            char* const p = buffer_ptr + n_chars;
+            dtoa_impl::store_msb_first(p, (first << (8 * leading)) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 8 - leading, dtoa_impl::eight_digit_bytes(middle) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 16 - leading, dtoa_impl::eight_digit_bytes(low16 - (middle * 100000000u)) + 0x3030303030303030u);
+            write_buffer_pos += n_chars + 24 - leading;
+            return;
+        }
+
         n_chars += count_digits(abs_value);
 
         // spare 1 byte for '\0'
@@ -2122,6 +2139,23 @@ class serializer
         }
     }
 
+    /// whether every number_magnitude_t fits 64 bits
+    static constexpr bool magnitude_has_at_most_64_bits = std::numeric_limits<number_magnitude_t>::is_specialized
+        && std::numeric_limits<number_magnitude_t>::digits <= 64;
+
+    /// whether @a x fits 64 bits: always if number_magnitude_t has at most
+    /// 64 bits (selected by type, as the comparison would be reported as
+    /// always true), else compared
+    static bool magnitude_fits_64_bits(const number_magnitude_t& /*unused*/, std::true_type /*unused*/) noexcept
+    {
+        return true;
+    }
+
+    static bool magnitude_fits_64_bits(const number_magnitude_t& x, std::false_type /*unused*/) noexcept
+    {
+        return x <= 18446744073709551615u;
+    }
+
     /*
      * Helper function for dump_integer
      *

include/nlohmann/detail/view/builder.hpp

@@ -343,6 +343,21 @@ class builder
                 }
                 arena_ensure(w, w_end, 4);
                 w = put_utf8(w, cp);
+                // A chain of unicode escapes ("\u3042\u3044\u3046", as Python's json.dumps writes non-ASCII text) is
+                // decoded here, without going round the loop above for each of them. Anything else (a surrogate, a
+                // bad digit, fewer than six bytes) leaves p at the backslash: the loop above handles it, and reports
+                // the same error at the same position as it would without this loop.
+                while (end - p >= 6 && p[0] == '\\' && p[1] == 'u')
+                {
+                    const int next = hex_codepoint(p + 2);
+                    if (next < 0 || (next & 0xF800) == 0xD800)
+                    {
+                        break;
+                    }
+                    p += 6;
+                    arena_ensure(w, w_end, 4);
+                    w = put_utf8(w, next);
+                }
             }
             else if (NLOHMANN_VIEW_LIKELY(d < 128 && simple_escape[d] != 0))
             {

single_include/nlohmann/json.hpp

@@ -12377,78 +12377,6 @@ JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline bool vector_utf8_run(cons
     block_out = block;
     return false;
 }
-
-/*!
-@brief skip 16-byte blocks of well-formed UTF-8 at p (a character boundary)
-
-Like vector_utf8_run, but quotes, backslashes, and control characters are
-ordinary characters. Returns the start of the first block in which the check
-found an error (which may belong to a sequence begun in the block before) or
-where fewer than 16 bytes are left; a sequence may be cut at that point, so the
-caller resumes at its start, one sequence at a time.
-*/
-JSON_SCAN_SSSE3_TARGET JSON_HEDLEY_NEVER_INLINE inline const unsigned char* vector_utf8_valid_blocks(const unsigned char* block, const unsigned char* e) noexcept
-{
-    using lookup = utf8_lookup4<>;
-#if JSON_SCAN_NEON
-    const uint8x16_t t1h = vld1q_u8(lookup::byte_1_high.data());
-    const uint8x16_t t1l = vld1q_u8(lookup::byte_1_low.data());
-    const uint8x16_t t2h = vld1q_u8(lookup::byte_2_high.data());
-    uint8x16_t prev = vdupq_n_u8(0);
-    while (e - block >= 16)
-    {
-        const uint8x16_t in = vld1q_u8(block);
-        if (vmaxvq_u8(vorrq_u8(in, prev)) < 0x80)
-        {
-            // ASCII here, and no sequence from the block before to finish
-            prev = in;
-            block += 16;
-            continue;
-        }
-        const uint8x16_t prev1 = vextq_u8(prev, in, 15);
-        const uint8x16_t sc = vandq_u8(vandq_u8(vqtbl1q_u8(t1h, vshrq_n_u8(prev1, 4)), vqtbl1q_u8(t1l, vandq_u8(prev1, vdupq_n_u8(0x0F)))), vqtbl1q_u8(t2h, vshrq_n_u8(in, 4)));
-        const uint8x16_t must23 = vorrq_u8(vqsubq_u8(vextq_u8(prev, in, 14), vdupq_n_u8(0xE0 - 0x80)), vqsubq_u8(vextq_u8(prev, in, 13), vdupq_n_u8(0xF0 - 0x80)));
-        const uint8x16_t err = veorq_u8(vandq_u8(must23, vdupq_n_u8(0x80)), sc);
-        if (vmaxvq_u8(err) != 0)
-        {
-            break;
-        }
-        prev = in;
-        block += 16;
-    }
-#else
-    const __m128i t1h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_high.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i t1l = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_1_low.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i t2h = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(lookup::byte_2_high.data()))); // NOLINT(bugprone-casting-through-void)
-    const __m128i nibble = _mm_set1_epi8(0x0F);
-    const __m128i zero = _mm_setzero_si128();
-    __m128i prev = zero;
-    while (e - block >= 16)
-    {
-        const __m128i in = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(block))); // NOLINT(bugprone-casting-through-void)
-        if (_mm_movemask_epi8(_mm_or_si128(in, prev)) == 0)
-        {
-            prev = in;
-            block += 16;
-            continue;
-        }
-        const __m128i prev1 = _mm_alignr_epi8(in, prev, 15);
-        const __m128i sc = _mm_and_si128(_mm_and_si128(_mm_shuffle_epi8(t1h, _mm_and_si128(_mm_srli_epi16(prev1, 4), nibble)),
-                                         _mm_shuffle_epi8(t1l, _mm_and_si128(prev1, nibble))),
-                                         _mm_shuffle_epi8(t2h, _mm_and_si128(_mm_srli_epi16(in, 4), nibble)));
-        const __m128i must23 = _mm_or_si128(_mm_subs_epu8(_mm_alignr_epi8(in, prev, 14), _mm_set1_epi8(0xE0 - 0x80)),
-                                            _mm_subs_epu8(_mm_alignr_epi8(in, prev, 13), _mm_set1_epi8(0xF0 - 0x80)));
-        const __m128i err = _mm_xor_si128(_mm_and_si128(must23, _mm_set1_epi8(static_cast<char>(-128))), sc);
-        if (_mm_movemask_epi8(_mm_cmpeq_epi8(err, zero)) != 0xFFFF)
-        {
-            break;
-        }
-        prev = in;
-        block += 16;
-    }
-#endif
-    return block;
-}
 #endif
 
 }  // namespace detail
@@ -12676,64 +12604,6 @@ inline std::size_t valid_utf8_prefix(const unsigned char* data, std::size_t n) n
     return pos;
 }
 
-/*!
-@brief whether [data, data+n) is valid UTF-8, for checking whole strings
-
-The same answer as valid_utf8_prefix(data, n) == n. Short ASCII strings, the
-most common keys and values, are decided in one test, and long strings are
-checked 16 bytes at a time where the vector check is available.
-*/
-inline bool valid_utf8_string(const unsigned char* data, std::size_t n) noexcept
-{
-    constexpr std::uint64_t high = 0x8080808080808080ull;
-    if (n <= 16)
-    {
-        // two overlapping words cover 8 to 16 bytes, one partial word fewer
-        std::uint64_t first = 0;
-        std::uint64_t last = 0;
-        if (n >= 8)
-        {
-            std::memcpy(&first, data, sizeof(first));
-            std::memcpy(&last, data + n - 8, sizeof(last));
-        }
-        else if (n != 0)
-        {
-            std::memcpy(&first, data, n);
-        }
-        if (((first | last) & high) == 0)
-        {
-            return true;
-        }
-    }
-#if JSON_SCAN_VECTOR_UTF8
-    else if (n >= 32
-#if JSON_SCAN_SSSE3_DISPATCH
-             && cpu_has_ssse3()
-#endif
-            )
-    {
-        const unsigned char* block = vector_utf8_valid_blocks(data, data + n);
-        // the rest from the start of a sequence that may be cut at block
-        for (int i = 1; i <= 3 && block - i >= data; ++i)
-        {
-            const unsigned char c = block[-i];
-            if (c < 0x80)
-            {
-                break;
-            }
-            if (c >= 0xC0)
-            {
-                block -= i;
-                break;
-            }
-        }
-        const auto checked = static_cast<std::size_t>(block - data);
-        return checked + valid_utf8_prefix(block, n - checked) == n;
-    }
-#endif
-    return valid_utf8_prefix(data, n) == n;
-}
-
 #if JSON_SCAN_VECTOR_UTF8
 /// the end of scan_string_vector from block, where the vector loop stopped
 /// (ill-formed UTF-8, or fewer than 16 bytes left): one byte or sequence at a
@@ -22199,19 +22069,6 @@ class binary_reader
         return get_bytes(len, "string", result);
     }
 
-    /// whether @a s is valid UTF-8: ASCII eight bytes at a time, the rest
-    /// sequence by sequence (as the binary writers check strings)
-    static bool is_valid_utf8_string(const string_t& s, std::true_type /*is_byte*/) noexcept
-    {
-        return valid_utf8_string(reinterpret_cast<const unsigned char*>(s.data()), s.size());
-    }
-
-    /// whether @a s, of a character type wider than a byte, is valid UTF-8
-    static bool is_valid_utf8_string(const string_t& s, std::false_type /*is_byte*/) noexcept
-    {
-        return is_valid_utf8(s);
-    }
-
     /*!
     @brief validate a decoded text string (value or object key) against @ref error_handler
 
@@ -22231,16 +22088,7 @@ class binary_reader
     */
     bool check_string_utf8(string_t& result, const char* context)
     {
-        return error_handler == error_handler_t::keep || check_string_utf8_handler(result, context);
+        if (error_handler == error_handler_t::keep || is_valid_utf8(result))
-    }
-
-    /// @ref check_string_utf8 for an error handler other than @ref
-    /// error_handler_t::keep; out of line, so that reading strings without a
-    /// check does not pay for the code of the check
-    JSON_HEDLEY_NEVER_INLINE
-    bool check_string_utf8_handler(string_t& result, const char* context)
-    {
-        if (is_valid_utf8_string(result, std::integral_constant<bool, sizeof(typename string_t::value_type) == 1>()))
         {
             return true;
         }
@@ -30458,25 +30306,6 @@ class binary_writer
         }
     }
 
-    /// write the head and the characters of @a value, at most
-    /// max_text_in_reservation of them, in one reservation
-    JSON_HEDLEY_ALWAYS_INLINE void write_cbor_string_reserved(const string_t& value)
-    {
-        CharType* const out = oa.reserve(value.size() + 2);
-        CharType* p = out;
-        if (value.size() <= 0x17)
-        {
-            *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
-        }
-        else
-        {
-            *p++ = to_char_type(0x78);
-            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-        }
-        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-        oa.commit(static_cast<std::size_t>(p - out) + value.size());
-    }
-
     /*!
     @brief write a CBOR text string
 
@@ -30498,7 +30327,19 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                write_cbor_string_reserved(value);
+                CharType* const out = oa.reserve(value.size() + 2);
+                CharType* p = out;
+                if (value.size() <= 0x17)
+                {
+                    *p++ = to_char_type(static_cast<std::uint8_t>(0x60 + value.size()));
+                }
+                else
+                {
+                    *p++ = to_char_type(0x78);
+                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+                }
+                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -30512,13 +30353,6 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_cbor_checked_string(const string_t& value, const BasicJsonType& context)
     {
-        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
-        {
-            check_utf8(value, context);
-            write_cbor_string_reserved(value);
-            return;
-        }
-
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -30533,27 +30367,6 @@ class binary_writer
     // MsgPack //
     /////////////
 
-    /// write the head and the characters of @a value, at most
-    /// max_text_in_reservation of them, in one reservation
-    JSON_HEDLEY_ALWAYS_INLINE void write_msgpack_string_reserved(const string_t& value)
-    {
-        CharType* const out = oa.reserve(value.size() + 2);
-        CharType* p = out;
-        if (value.size() <= 31)
-        {
-            // fixstr
-            *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
-        }
-        else
-        {
-            // str 8
-            *p++ = to_char_type(0xD9);
-            *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
-        }
-        copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
-        oa.commit(static_cast<std::size_t>(p - out) + value.size());
-    }
-
     /*!
     @brief write a MessagePack str
 
@@ -30571,7 +30384,21 @@ class binary_writer
             // the string is written as it is: head and characters in one reservation
             if (JSON_HEDLEY_LIKELY(value.size() <= max_text_in_reservation))
             {
-                write_msgpack_string_reserved(value);
+                CharType* const out = oa.reserve(value.size() + 2);
+                CharType* p = out;
+                if (value.size() <= 31)
+                {
+                    // fixstr
+                    *p++ = to_char_type(static_cast<std::uint8_t>(0xA0 | value.size()));
+                }
+                else
+                {
+                    // str 8
+                    *p++ = to_char_type(0xD9);
+                    *p++ = to_char_type(static_cast<std::uint8_t>(value.size()));
+                }
+                copy_characters(p, reinterpret_cast<const CharType*>(value.data()), value.size());
+                oa.commit(static_cast<std::size_t>(p - out) + value.size());
                 return;
             }
         }
@@ -30584,13 +30411,6 @@ class binary_writer
     JSON_HEDLEY_NEVER_INLINE
     void write_msgpack_checked_string(const string_t& value, const BasicJsonType& context)
     {
-        if (error_handler == error_handler_t::strict && value.size() <= max_text_in_reservation)
-        {
-            check_utf8(value, context);
-            write_msgpack_string_reserved(value);
-            return;
-        }
-
         string_t storage;
         const string_t& sanitized = sanitize_utf8_for_write(value, context, storage);
 
@@ -32200,9 +32020,10 @@ class binary_writer
     static void check_utf8(const string_t& s, const BasicJsonType& context)
     {
         const auto* data = reinterpret_cast<const unsigned char*>(s.data());
-        if (JSON_HEDLEY_UNLIKELY(!valid_utf8_string(data, s.size())))
+        const std::size_t valid = valid_utf8_prefix(data, s.size());
+        if (JSON_HEDLEY_UNLIKELY(valid != s.size()))
         {
-            throw_invalid_utf8(data, valid_utf8_prefix(data, s.size()), context);
+            throw_invalid_utf8(data, valid, context);
         }
     }
 
@@ -36403,6 +36224,23 @@ class serializer
             return;
         }
 
+        // 17 to 20 digits: the first one to four, then twice eight
+        if (magnitude_fits_64_bits(abs_value, std::integral_constant<bool, magnitude_has_at_most_64_bits>()))
+        {
+            const auto value = static_cast<std::uint64_t>(abs_value);
+            const std::uint64_t top = value / 10000000000000000u; // 1 to 1844
+            const std::uint64_t low16 = value - (top * 10000000000000000u);
+            const std::uint64_t middle = low16 / 100000000u;
+            const std::uint64_t first = dtoa_impl::eight_digit_bytes(top);
+            const auto leading = static_cast<unsigned>(count_leading_zeros(first) / 8); // (first is not 0)
+            char* const p = buffer_ptr + n_chars;
+            dtoa_impl::store_msb_first(p, (first << (8 * leading)) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 8 - leading, dtoa_impl::eight_digit_bytes(middle) + 0x3030303030303030u);
+            dtoa_impl::store_msb_first(p + 16 - leading, dtoa_impl::eight_digit_bytes(low16 - (middle * 100000000u)) + 0x3030303030303030u);
+            write_buffer_pos += n_chars + 24 - leading;
+            return;
+        }
+
         n_chars += count_digits(abs_value);
 
         // spare 1 byte for '\0'
@@ -36548,6 +36386,23 @@ class serializer
         }
     }
 
+    /// whether every number_magnitude_t fits 64 bits
+    static constexpr bool magnitude_has_at_most_64_bits = std::numeric_limits<number_magnitude_t>::is_specialized
+        && std::numeric_limits<number_magnitude_t>::digits <= 64;
+
+    /// whether @a x fits 64 bits: always if number_magnitude_t has at most
+    /// 64 bits (selected by type, as the comparison would be reported as
+    /// always true), else compared
+    static bool magnitude_fits_64_bits(const number_magnitude_t& /*unused*/, std::true_type /*unused*/) noexcept
+    {
+        return true;
+    }
+
+    static bool magnitude_fits_64_bits(const number_magnitude_t& x, std::false_type /*unused*/) noexcept
+    {
+        return x <= 18446744073709551615u;
+    }
+
     /*
      * Helper function for dump_integer
      *

single_include/nlohmann/json_view.hpp

@@ -1585,6 +1585,21 @@ class builder
                 }
                 arena_ensure(w, w_end, 4);
                 w = put_utf8(w, cp);
+                // A chain of unicode escapes ("\u3042\u3044\u3046", as Python's json.dumps writes non-ASCII text) is
+                // decoded here, without going round the loop above for each of them. Anything else (a surrogate, a
+                // bad digit, fewer than six bytes) leaves p at the backslash: the loop above handles it, and reports
+                // the same error at the same position as it would without this loop.
+                while (end - p >= 6 && p[0] == '\\' && p[1] == 'u')
+                {
+                    const int next = hex_codepoint(p + 2);
+                    if (next < 0 || (next & 0xF800) == 0xD800)
+                    {
+                        break;
+                    }
+                    p += 6;
+                    arena_ensure(w, w_end, 4);
+                    w = put_utf8(w, next);
+                }
             }
             else if (NLOHMANN_VIEW_LIKELY(d < 128 && simple_escape[d] != 0))
             {

tests/src/unit-guard-page.cpp

@@ -403,7 +403,6 @@ TEST_CASE("guard page")
                     CHECK(nlohmann::detail::find_string_special(p, n) <= n);
                     CHECK(nlohmann::detail::find_ascii_copyable_run(p, n) <= n);
                     CHECK(nlohmann::detail::valid_utf8_prefix(p, n) <= n);
-                    CHECK(nlohmann::detail::valid_utf8_string(p, n) == (nlohmann::detail::valid_utf8_prefix(p, n) == n));
 #if defined(JSON_USE_SIMDUTF) && defined(JSON_HAS_CPP_17)
                     CHECK(nlohmann::detail::find_string_delimiter(p, n) <= n);
 #endif

tests/src/unit-json_view_builder.cpp

@@ -575,6 +575,59 @@ TEST_CASE("json_view builder: escapes between runs of text")
     }
 }
 
+TEST_CASE("json_view builder: chains of unicode escapes")
+{
+    // Consecutive \uXXXX escapes are decoded in a loop of their own. Chains of
+    // every length from 1 to 40 of escapes that give one, two, and three
+    // bytes of UTF-8, in upper and lower case, followed by what ends a chain:
+    // the end of the string, text, another escape, UTF-8, and everything that
+    // is not a valid escape (a bad digit at every position of the last
+    // escape, a lone surrogate, a surrogate pair, a cut in every place).
+    const std::array<const char*, 8> chain = {{"\\u0041", "\\u00e4", "\\u00E4", "\\u20ac", "\\u3042", "\\uFFFF", "\\u0000", "\\u07ff"}};
+    const std::array<const char*, 12> ends = {{"", "abc", "\\n", "\\u00e9", "\\ud83d\\ude00", "\\ud83d", "\\ude00", "\\ud83d\\u0041", "\\u12G4", "\\u12", "\xc3\xa4", "\\"}};
+    std::mt19937 rng(2027); // NOLINT(cert-msc32-c,cert-msc51-cpp,bugprone-random-generator-seed): reproducible
+    for (std::size_t length = 1; length <= 40; ++length)
+    {
+        for (int i = 0; i < 20; ++i)
+        {
+            std::string content = std::string(rng() % 20, 'a');
+            for (std::size_t k = 0; k < length; ++k)
+            {
+                content += chain[rng() % chain.size()];
+            }
+            const std::string whole = content;
+            for (const char* end : ends)
+            {
+                check_string(whole + end);
+                check_string(whole + end + std::string(rng() % 19, 'z'));
+            }
+            // a bad digit at every position of every escape near the end of the chain
+            for (std::size_t back = 1; back <= 6 && back <= length; ++back)
+            {
+                for (std::size_t digit = 2; digit < 6; ++digit)
+                {
+                    std::string broken = whole;
+                    broken[broken.size() - (6 * back) + digit] = "gG\"\x01 z"[rng() % 6];
+                    check_string(broken);
+                }
+            }
+            // the text cut in every place of the last three escapes
+            for (std::size_t cut = 0; cut <= 18 && cut <= whole.size(); ++cut)
+            {
+                check_string(whole.substr(0, whole.size() - cut));
+            }
+        }
+    }
+    // a chain longer than the first growth of the arena, in a key and in a value
+    std::string long_chain;
+    for (int i = 0; i < 3000; ++i)
+    {
+        long_chain += chain[static_cast<std::size_t>(i) % chain.size()];
+    }
+    check_string(long_chain);
+    check_string(long_chain + "\\ud83d\\ude00" + long_chain);
+}
+
 TEST_CASE("json_view node integer bits")
 {
     using nlohmann::detail::view::integer_bits;

tests/src/unit-json_view_from_json.cpp

@@ -443,6 +443,30 @@ TEST_CASE("json_view from_json")
         CHECK(d.root().materialize().get<point>().x == 3);
     }
 
+    SECTION("escaped keys: members are found by their decoded names")
+    {
+        // keys are decoded before they are compared, as by parse(); a lookup
+        // that compares the raw bytes of the source would miss these members
+        const json_document d = json_document::parse(R"([{"\u0078": 1, "y": 2}, {"V\u0061lue": 3, "Te\u0078t": "t"}, {"\u0062": "escaped"}, {"x": 1, "\u0078": 3, "y": 2}])");
+        const json j = d.root().materialize();
+        CHECK(d.root()[0].get<point>().x == 1);
+        CHECK(d.root()[0].get<point>().y == 2);
+        CHECK((d.root()[0].get<point>() == j[0].get<point>()));
+        CHECK(d.root()[1].get<with_names>().value == 3);
+        CHECK(d.root()[1].get<with_names>().text == "t");
+        CHECK(d.root()[2].get<with_defaults>().b == "escaped");
+        CHECK(d.root()[2].get<with_defaults>().a == 1);
+        // a duplicate key written once plain and once escaped: still the first member
+        CHECK(d.root()[3].get<point>().x == 1);
+        CHECK(j[3].get<point>().x == 3);
+#if !defined(JSON_NOEXCEPTION) && !JSON_DIAGNOSTICS && !JSON_DIAGNOSTIC_POSITIONS
+        // an escaped backslash is part of the decoded key: "x\\" is not "x"
+        const json_document e = json_document::parse(R"({"x\\": 1, "y": 2})");
+        CHECK(exception_of_call([&] { static_cast<void>(e.root().get<point>()); }) == exception_of_call([&] { static_cast<void>(e.root().materialize().get<point>()); }));
+        CHECK(exception_of_call([&] { static_cast<void>(e.root().get<point>()); }) == "[json.exception.out_of_range.403] key 'x' not found");
+#endif
+    }
+
     SECTION("editable documents and ordered_json")
     {
         json_editable_document e = json_editable_document::parse(R"({"x": 1, "y": 2})");

tests/src/unit-serialization.cpp

@@ -23,6 +23,7 @@ using nlohmann::json;
 #include <cstdint>
 #include <sstream>
 #include <iomanip>
+#include <limits>
 #include <string>
 #include <vector>
 
@@ -248,6 +249,51 @@ TEST_CASE_TEMPLATE("serialization for extreme integer values", T, int32_t, uint3
     }
 }
 
+TEST_CASE("integers of every digit count are written like std::to_string")
+{
+    // dump_integer() writes up to 16 digits in two groups of eight and 17 to
+    // 20 digits as one to four digits and two groups of eight
+    std::vector<std::uint64_t> values;
+    std::uint64_t power = 1;
+    for (int digits = 1; digits <= 20; ++digits)
+    {
+        values.push_back(power);                     // 1 followed by zeros
+        values.push_back(power + 1);
+        values.push_back((power * 2) - 1);
+        if (digits < 20)
+        {
+            values.push_back((power * 10) - 1);      // all 9s
+            values.push_back((power * 10) - power);  // 9 followed by zeros
+            power *= 10;
+        }
+    }
+    values.push_back((std::numeric_limits<std::uint64_t>::max)());
+    values.push_back(static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()));
+    values.push_back(static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()) + 1);
+    std::uint64_t state = 0x9E3779B97F4A7C15u;
+    for (int i = 0; i < 20000; ++i)
+    {
+        state = (state * 6364136223846793005u) + 1442695040888963407u;
+        values.push_back(state >> (state % 61));     // every bit length
+    }
+
+    for (const auto v : values)
+    {
+        CAPTURE(v)
+        CHECK(json(v).dump() == std::to_string(v));
+        if (v <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
+        {
+            const auto s = static_cast<std::int64_t>(v);
+            CHECK(json(s).dump() == std::to_string(s));
+            CHECK(json(-s).dump() == std::to_string(-s));
+        }
+    }
+    CHECK(json((std::numeric_limits<std::int64_t>::min)()).dump() == "-9223372036854775808");
+
+    // in a container, so the digits are followed by other output
+    CHECK(json::array({std::uint64_t{18446744073709551615u}, std::int64_t{-1234567890123456789}, 1}).dump() == "[18446744073709551615,-1234567890123456789,1]");
+}
+
 TEST_CASE("dump with binary values")
 {
     auto binary = json::binary({1, 2, 3, 4});

tests/src/unit-unicode.cpp

@@ -13,7 +13,6 @@ using nlohmann::json;
 
 #include <algorithm>
 #include <fstream>
-#include <random>
 #include <string>
 #include "make_test_data_available.hpp"
 #include "test_utils.hpp"
@@ -1632,40 +1631,3 @@ TEST_CASE("Unicode RFC 3629")
 }
 
 DOCTEST_CLANG_SUPPRESS_WARNING_POP
-
-TEST_CASE("UTF-8 check of whole strings")
-{
-    // valid_utf8_string() decides short strings with a word test and long ones
-    // 16 bytes at a time where a vector check is available; it must agree with
-    // the byte-wise check for every mix of ASCII, sequences of each length,
-    // ill-formed and truncated sequences, at every length and offset
-    const char* const pieces[] =
-    {
-        "a", "\x7F", "\xC3\xA9", "\xE2\x82\xAC", "\xE0\xA0\x80", "\xEF\xBF\xBF", "\xF0\x9F\x98\x80", "\xF4\x8F\xBF\xBF",
-        "\x80", "\xC0\xAF", "\xC3", "\xE2\x82", "\xED\xA0\x80", "\xF0\x9F", "\xF4\x90\x80\x80", "\xFF"
-    };
-    // std::mt19937's sequence is fixed by the standard; no distribution is used
-    std::mt19937 rng(5);
-    std::size_t valid = 0;
-    for (int i = 0; i < 100000; ++i)
-    {
-        std::string s;
-        const std::size_t length = rng() % 100;
-        const std::uint32_t ascii = rng() % 101;
-        while (s.size() < length)
-        {
-            // mostly well-formed pieces (the first eight), so that long valid
-            // strings are common
-            s += (rng() % 100 < ascii) ? std::string("x") : std::string(pieces[rng() % (rng() % 8 == 0 ? 16 : 8)]);
-        }
-        const auto* data = reinterpret_cast<const unsigned char*>(s.data());
-        const bool expected = nlohmann::detail::is_valid_utf8(s);
-        valid += expected ? 1 : 0;
-        CAPTURE(s)
-        CHECK(nlohmann::detail::valid_utf8_string(data, s.size()) == expected);
-        CHECK((nlohmann::detail::valid_utf8_prefix(data, s.size()) == s.size()) == expected);
-    }
-    // both outcomes are common enough to be tested
-    CHECK(valid > 20000);
-    CHECK(valid < 80000);
-}