Keep the serializer's buffers out of -Weffc++ and cpplint warnings

GCC's -Weffc++ asks for the three buffers in the member initialization
list, which would zero them again. They are now of a type with an empty
user-provided constructor (as the json_view builder's frame stack), so
they are listed there and stay uninitialized.

The 8-to-31-byte branch of the short-string writer no longer spans an
#if with a dangling else, which cpplint read as an else body without
braces.

dump() instructions (Apple clang, twitter/citm/canada, compact and
indented) are unchanged within noise (-0.3 % to +0.6 %).

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

docs/mkdocs/docs/home/architecture.md

@@ -339,11 +339,6 @@ The `serializer` (used by [`dump`](../api/basic_json/dump.md) and [`operator<<`]
 - `output_stream_adapter` writes to a `std::ostream`.
 - `output_string_adapter` appends to a string.
 
-The `binary_writer` does not call an adapter for every byte. The `to_*` functions that return a `std::vector` write
-into the vector through a sink (`output_vector_sink`) that is not virtual. The functions that take an output adapter
-write through a sink (`output_adapter_sink`) that collects the output in a buffer of one kibibyte and passes it to the
-adapter in blocks, so that the adapter is called (and a stream locked) once per block instead of once per value.
-
 ## Value conversion
 
 Values are converted from and to other types with the `JSONSerializer` template parameter. The default,

include/nlohmann/detail/macro_unscope.hpp

@@ -33,6 +33,7 @@
 #undef JSON_SCAN_SSSE3_TARGET
 #undef JSON_SCAN_VECTOR
 #undef JSON_SCAN_VECTOR_UTF8
+#undef JSON_DUMP_SHORT_STRINGS
 
 #ifndef JSON_TEST_KEEP_MACROS
     #undef JSON_CATCH

include/nlohmann/detail/output/output_adapters.hpp

@@ -55,66 +55,6 @@ using output_adapter_t = std::shared_ptr<output_adapter_protocol<CharType>>;
 /// output_vector_sink also appends writes of at least this size with insert()
 constexpr std::size_t max_reserve_size = 256;
 
-/// @brief copy @a length characters, at most 32, without a call of memcpy()
-///
-/// Short strings are the typical payload of a binary value, and a call of
-/// memcpy() costs more than copying them. A copy of 16 to 32 characters is two
-/// possibly overlapping 16-byte copies, one of 8 to 15 two 8-byte copies, and
-/// so on down to a single character; each is a fixed-size load and store.
-/// Nothing outside of [src, src + length) is read or written.
-template<typename CharType>
-inline void copy_short(CharType* dst, const CharType* src, const std::size_t length, std::true_type /*is_byte*/) noexcept
-{
-    JSON_ASSERT(length <= 32);
-    if (length >= 16)
-    {
-        std::array<char, 16> first; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::array<char, 16> last; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::memcpy(first.data(), src, 16);
-        std::memcpy(last.data(), src + (length - 16), 16);
-        std::memcpy(dst, first.data(), 16);
-        std::memcpy(dst + (length - 16), last.data(), 16);
-    }
-    else if (length >= 8)
-    {
-        std::array<char, 8> first; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::array<char, 8> last; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::memcpy(first.data(), src, 8);
-        std::memcpy(last.data(), src + (length - 8), 8);
-        std::memcpy(dst, first.data(), 8);
-        std::memcpy(dst + (length - 8), last.data(), 8);
-    }
-    else if (length >= 4)
-    {
-        std::array<char, 4> first; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::array<char, 4> last; // NOLINT(cppcoreguidelines-pro-type-member-init,hicpp-member-init): written before read
-        std::memcpy(first.data(), src, 4);
-        std::memcpy(last.data(), src + (length - 4), 4);
-        std::memcpy(dst, first.data(), 4);
-        std::memcpy(dst + (length - 4), last.data(), 4);
-    }
-    else if (length != 0)
-    {
-        // 1 to 3: the first, the middle, and the last character
-        const CharType a = src[0];
-        const CharType b = src[length >> 1];
-        const CharType c = src[length - 1];
-        dst[0] = a;
-        dst[length >> 1] = b;
-        dst[length - 1] = c;
-    }
-}
-
-/// @brief copy @a length characters, of a character type wider than a byte
-template<typename CharType>
-inline void copy_short(CharType* dst, const CharType* src, const std::size_t length, std::false_type /*is_byte*/) noexcept
-{
-    std::memcpy(dst, src, length * sizeof(CharType));
-}
-
-/// the number of characters an empty vector is grown to by output_vector_sink
-constexpr std::size_t min_vector_sink_capacity = 64;
-
 /// @brief non-virtual output sink writing into a std::vector
 ///
 /// This sink is not part of the virtual output_adapter_protocol hierarchy: it is
@@ -138,7 +78,7 @@ class output_vector_sink
 {
   public:
     explicit output_vector_sink(std::vector<CharType, AllocatorType>& vec) noexcept
-        : v(&vec), cursor(vec.data() + vec.size()), limit(cursor)
+        : v(&vec), position(vec.size())
     {}
 
     output_vector_sink(const output_vector_sink&) = delete;
@@ -146,7 +86,7 @@ class output_vector_sink
     output_vector_sink& operator=(output_vector_sink&&) = delete;
 
     output_vector_sink(output_vector_sink&& other) noexcept
-        : v(other.v), cursor(other.cursor), limit(other.limit)
+        : v(other.v), position(other.position)
     {
         other.v = nullptr;
     }
@@ -155,7 +95,7 @@ class output_vector_sink
     {
         if (v != nullptr)
         {
-            v->resize(position());
+            v->resize(position);
         }
     }
 
@@ -164,11 +104,11 @@ class output_vector_sink
     JSON_HEDLEY_ALWAYS_INLINE
     void write_character(CharType c)
     {
-        if (JSON_HEDLEY_UNLIKELY(cursor == limit))
+        if (JSON_HEDLEY_UNLIKELY(position == v->size()))
         {
             grow(1);
         }
-        *cursor++ = c;
+        (*v)[position++] = c;
     }
 
     // no JSON_HEDLEY_NON_NULL here: binary_writer legitimately passes a null
@@ -177,7 +117,7 @@ class output_vector_sink
     JSON_HEDLEY_ALWAYS_INLINE
     void write_characters(const CharType* s, std::size_t length)
     {
-        if (JSON_HEDLEY_UNLIKELY(space() < length))
+        if (JSON_HEDLEY_UNLIKELY(v->size() - position < length))
         {
             if (length >= max_reserve_size)
             {
@@ -186,15 +126,10 @@ class output_vector_sink
             }
             grow(length);
         }
-        if (length <= 32)
+        if (length != 0)
         {
-            copy_short(cursor, s, length, std::integral_constant<bool, sizeof(CharType) == 1>());
+            std::memcpy(v->data() + position, s, length * sizeof(CharType));
-            cursor += length;
+            position += length;
-        }
-        else
-        {
-            std::memcpy(cursor, s, length * sizeof(CharType));
-            cursor += length;
         }
     }
 
@@ -209,37 +144,21 @@ class output_vector_sink
     CharType* reserve(const std::size_t length)
     {
         JSON_ASSERT(length <= max_reserve_size);
-        if (JSON_HEDLEY_UNLIKELY(space() < length))
+        if (JSON_HEDLEY_UNLIKELY(v->size() - position < length))
         {
             grow(length);
         }
-        return cursor;
+        return v->data() + position;
     }
 
     /// keep the first @a length characters written to the space from reserve()
     JSON_HEDLEY_ALWAYS_INLINE
     void commit(const std::size_t length) noexcept
     {
-        cursor += length;
+        position += length;
     }
 
-    /// nothing to pass on: the characters are in the vector (see output_adapter_sink)
-    void flush() noexcept
-    {}
-
   private:
-    /// number of characters of *v written so far
-    std::size_t position() const noexcept
-    {
-        return static_cast<std::size_t>(cursor - v->data());
-    }
-
-    /// number of characters that fit the vector behind the write position
-    std::size_t space() const noexcept
-    {
-        return static_cast<std::size_t>(limit - cursor);
-    }
-
     /// make room for at least @a length more characters after the position;
     /// kept out of line so that the write functions stay small enough for
     /// GCC to inline them into the writer
@@ -247,15 +166,12 @@ class output_vector_sink
     void grow(const std::size_t length)
     {
         // use the capacity the vector already has, else at least double it;
-        // never less than min_vector_sink_capacity, so that a small value does not
+        // never less than 64 characters, so that a small value does not
         // reallocate for every few bytes
-        const std::size_t written = position();
+        const std::size_t needed = position + length;
-        const std::size_t needed = written + length;
+        v->resize((std::max)(std::size_t{64}, needed <= v->capacity()
-        v->resize((std::max)(min_vector_sink_capacity, needed <= v->capacity()
                              ? v->capacity()
                              : (std::max)(needed, v->capacity() * 2)));
-        cursor = v->data() + written;
-        limit = v->data() + v->size();
     }
 
     /// append @a length (at least max_reserve_size) characters that do not fit
@@ -265,24 +181,20 @@ class output_vector_sink
     JSON_HEDLEY_NEVER_INLINE
     void append(const CharType* s, const std::size_t length)
     {
-        const std::size_t written = position();
+        v->resize(position);
-        v->resize(written);
+        if (v->capacity() - position < length)
-        if (v->capacity() - written < length)
         {
             // grow geometrically, with room for the writes that follow, so
             // that the next grow() need not reallocate right away
-            v->reserve((std::max)(v->capacity() * 2, written + length + max_reserve_size));
+            v->reserve((std::max)(v->capacity() * 2, position + length + max_reserve_size));
         }
         v->insert(v->end(), s, s + length);
-        cursor = v->data() + v->size();
+        position = v->size();
-        limit = cursor;
     }
 
     std::vector<CharType, AllocatorType>* v;
-    /// the write position: in *v, at the number of characters written so far
+    /// number of characters of *v written so far
-    CharType* cursor;
+    std::size_t position;
-    /// the end of *v
-    CharType* limit;
 };
 
 /// output adapter for byte vectors
@@ -365,17 +277,9 @@ class output_string_adapter : public output_adapter_protocol<CharType>
 ///
 /// Wraps the polymorphic output_adapter_t so the same binary_writer template can
 /// also target arbitrary adapters (output streams, strings, user-provided
-/// adapters) via the `output_adapter`-based overloads.
+/// adapters) via the `output_adapter`-based overloads. Each write still goes
-///
+/// through one virtual call, exactly as before; only the concrete sinks above
-/// A write through the adapter is a virtual call, and for a stream a call with
+/// avoid it.
-/// a sentry on top, which costs more than encoding the few bytes of most values.
-/// The sink therefore collects what is written in a buffer and passes it on in
-/// one piece when it is full, a write is too large for it, or @ref flush is
-/// called. Everything written reaches the adapter in the same order and with
-/// the same bytes; the destructor passes on what is left, so that a write that
-/// throws leaves the adapter with exactly the bytes written before it. Only
-/// @ref flush can report an error of the adapter (the destructor must not
-/// throw), so it has to be called once the value is written.
 template<typename CharType>
 class output_adapter_sink
 {
@@ -386,121 +290,36 @@ class output_adapter_sink
         JSON_ASSERT(oa);
     }
 
-    output_adapter_sink(const output_adapter_sink&) = delete;
-    output_adapter_sink& operator=(const output_adapter_sink&) = delete;
-    output_adapter_sink& operator=(output_adapter_sink&&) = delete;
-
-    output_adapter_sink(output_adapter_sink&& other) noexcept
-        : oa(std::move(other.oa)), used(other.used)
-    {
-        std::memcpy(buffer.data(), other.buffer.data(), other.used * sizeof(CharType));
-        other.used = 0;
-    }
-
-    ~output_adapter_sink()
-    {
-        // a normal return has flushed already, so this is for a write that threw
-        if (used != 0)
-        {
-            JSON_TRY
-            {
-                flush();
-            }
-            JSON_CATCH(...)
-            {
-                // nothing can be done about an adapter that throws here
-            }
-        }
-    }
-
-    JSON_HEDLEY_ALWAYS_INLINE
     void write_character(CharType c)
     {
-        if (JSON_HEDLEY_UNLIKELY(used == buffer_size))
+        oa->write_character(c);
-        {
-            flush();
-        }
-        buffer[used++] = c;
     }
 
     // no JSON_HEDLEY_NON_NULL: forwards (null, 0) for empty payloads, exactly as
     // the type-erased path already did before this sink existed
-    JSON_HEDLEY_ALWAYS_INLINE
     void write_characters(const CharType* s, std::size_t length)
     {
-        if (JSON_HEDLEY_UNLIKELY(buffer_size - used < length))
+        oa->write_characters(s, length);
-        {
-            write_large(s, length);
-            return;
-        }
-        if (length <= 32)
-        {
-            copy_short(buffer.data() + used, s, length, std::integral_constant<bool, sizeof(CharType) == 1>());
-            used += length;
-        }
-        else
-        {
-            std::memcpy(buffer.data() + used, s, length * sizeof(CharType));
-            used += length;
-        }
     }
 
     /// space for writing up to @a length characters (see
     /// output_vector_sink::reserve)
-    JSON_HEDLEY_ALWAYS_INLINE
+    CharType* reserve(const std::size_t length) noexcept
-    CharType* reserve(const std::size_t length)
     {
         JSON_ASSERT(length <= max_reserve_size);
-        if (JSON_HEDLEY_UNLIKELY(buffer_size - used < length))
+        static_cast<void>(length);
-        {
+        return reserved.data();
-            flush();
-        }
-        return buffer.data() + used;
     }
 
-    /// keep the first @a length characters written to the space from reserve()
+    /// write the first @a length characters written to the space from reserve()
-    JSON_HEDLEY_ALWAYS_INLINE
+    void commit(const std::size_t length)
-    void commit(const std::size_t length) noexcept
     {
-        used += length;
+        oa->write_characters(reserved.data(), length);
-    }
-
-    /// pass everything written so far on to the adapter
-    void flush()
-    {
-        if (used != 0)
-        {
-            // reset first: the characters count as written even if the adapter throws
-            const std::size_t length = used;
-            used = 0;
-            oa->write_characters(buffer.data(), length);
-        }
     }
 
   private:
-    /// a write that does not fit the space left in the buffer
-    JSON_HEDLEY_NEVER_INLINE
-    void write_large(const CharType* s, const std::size_t length)
-    {
-        flush();
-        if (length >= buffer_size)
-        {
-            oa->write_characters(s, length);
-        }
-        else
-        {
-            std::memcpy(buffer.data(), s, length * sizeof(CharType));
-            used = length;
-        }
-    }
-
-    /// large enough for reserve() at any time
-    static constexpr std::size_t buffer_size = 4 * max_reserve_size;
-
     output_adapter_t<CharType> oa;
-    /// number of characters of @ref buffer not yet passed on
+    std::array<CharType, max_reserve_size> reserved{};
-    std::size_t used = 0;
-    std::array<CharType, buffer_size> buffer{};
 };
 
 /// @brief whether std::basic_string<CharType> has a non-deprecated std::char_traits

include/nlohmann/detail/output/serializer.hpp

@@ -34,6 +34,14 @@
 #include <nlohmann/detail/string_utils.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
+// the short-string fast path of the serializer assembles words from little-endian
+// loads, see serializer::put_short_quoted()
+#if defined(_MSC_VER) || defined(__x86_64__) || defined(__i386__) || (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+    #define JSON_DUMP_SHORT_STRINGS 1
+#else
+    #define JSON_DUMP_SHORT_STRINGS 0
+#endif
+
 NLOHMANN_JSON_NAMESPACE_BEGIN
 namespace detail
 {
@@ -80,11 +88,14 @@ class serializer
                const std::size_t indent_step_ = 0,
                error_handler_t error_handler_ = error_handler_t::strict)
         : o(&s)
+        , number_buffer() // NOLINT(readability-redundant-member-init)
+        , string_buffer() // NOLINT(readability-redundant-member-init)
         , indent_char(ichar)
         , pretty_print(pretty_print_)
         , ensure_ascii(ensure_ascii_)
         , indent_step(indent_step_)
         , error_handler(error_handler_)
+        , write_buffer() // NOLINT(readability-redundant-member-init)
     {}
 
     // deleted because of pointer members
@@ -159,34 +170,27 @@ class serializer
 
                 if (pretty_print)
                 {
-                    put_literal("{\n");
-
                     // variable to hold indentation for recursive calls
                     const auto new_indent = next_indent(current_indent, indent_step);
 
+                    put_literal_indent("{\n", new_indent);
+
                     // first n-1 elements
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        put_indent(new_indent);
+                        put_quoted(i->first, "\": ");
-                        put_char('"');
+                        dump_element(i->second, new_indent, depth + 1);
-                        dump_escaped(i->first);
+                        put_literal_indent(",\n", new_indent);
-                        put_literal("\": ");
-                        dump_internal(i->second, new_indent, depth + 1);
-                        put_literal(",\n");
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    put_indent(new_indent);
+                    put_quoted(i->first, "\": ");
-                    put_char('"');
+                    dump_element(i->second, new_indent, depth + 1);
-                    dump_escaped(i->first);
-                    put_literal("\": ");
-                    dump_internal(i->second, new_indent, depth + 1);
 
-                    put_char('\n');
+                    put_literal_indent("\n", current_indent);
-                    put_indent(current_indent);
                     put_char('}');
                 }
                 else
@@ -197,20 +201,16 @@ class serializer
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        put_char('"');
+                        put_quoted(i->first, "\":");
-                        dump_escaped(i->first);
+                        dump_element(i->second, current_indent, depth + 1);
-                        put_literal("\":");
-                        dump_internal(i->second, current_indent, depth + 1);
                         put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    put_char('"');
+                    put_quoted(i->first, "\":");
-                    dump_escaped(i->first);
+                    dump_element(i->second, current_indent, depth + 1);
-                    put_literal("\":");
-                    dump_internal(i->second, current_indent, depth + 1);
 
                     put_char('}');
                 }
@@ -234,27 +234,24 @@ class serializer
 
                 if (pretty_print)
                 {
-                    put_literal("[\n");
-
                     // variable to hold indentation for recursive calls
                     const auto new_indent = next_indent(current_indent, indent_step);
 
+                    put_literal_indent("[\n", new_indent);
+
                     // first n-1 elements
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        put_indent(new_indent);
+                        dump_element(*i, new_indent, depth + 1);
-                        dump_internal(*i, new_indent, depth + 1);
+                        put_literal_indent(",\n", new_indent);
-                        put_literal(",\n");
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    put_indent(new_indent);
+                    dump_element(val.m_data.m_value.array->back(), new_indent, depth + 1);
-                    dump_internal(val.m_data.m_value.array->back(), new_indent, depth + 1);
 
-                    put_char('\n');
+                    put_literal_indent("\n", current_indent);
-                    put_indent(current_indent);
                     put_char(']');
                 }
                 else
@@ -265,13 +262,13 @@ class serializer
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        dump_internal(*i, current_indent, depth + 1);
+                        dump_element(*i, current_indent, depth + 1);
                         put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    dump_internal(val.m_data.m_value.array->back(), current_indent, depth + 1);
+                    dump_element(val.m_data.m_value.array->back(), current_indent, depth + 1);
 
                     put_char(']');
                 }
@@ -294,6 +291,27 @@ class serializer
     }
 
   private:
+    /*!
+    @brief serialize an element of a container
+
+    Most elements are scalars, which need none of the state dump_internal() keeps
+    for a container; writing them from here spares each the entry and exit of
+    that function.
+    */
+    JSON_HEDLEY_ALWAYS_INLINE void dump_element(const BasicJsonType& val,
+            const std::size_t current_indent,
+            const std::size_t depth)
+    {
+        if (val.m_data.m_type == value_t::object || val.m_data.m_type == value_t::array)
+        {
+            dump_internal(val, current_indent, depth);
+        }
+        else
+        {
+            dump_scalar(val, current_indent);
+        }
+    }
+
     /*!
     @brief write out @a val and everything below it without the call stack
 
@@ -353,16 +371,13 @@ class serializer
                     put_indent(frame.child_indent);
                 }
 
-                put_char('"');
-                dump_escaped(frame.object_it->first);
-
                 if (pretty_print)
                 {
-                    put_literal("\": ");
+                    put_quoted(frame.object_it->first, "\": ");
                 }
                 else
                 {
-                    put_literal("\":");
+                    put_quoted(frame.object_it->first, "\":");
                 }
 
                 const BasicJsonType& element = frame.object_it->second;
@@ -537,78 +552,13 @@ class serializer
         {
             case value_t::string:
             {
-                put_char('"');
+                dump_string_value(*val.m_data.m_value.string);
-                dump_escaped(*val.m_data.m_value.string);
-                put_char('"');
                 return;
             }
 
             case value_t::binary:
             {
-                if (pretty_print)
+                dump_binary_value(current_indent, *val.m_data.m_value.binary);
-                {
-                    put_literal("{\n");
-
-                    // variable to hold indentation for the bytes
-                    const auto new_indent = next_indent(current_indent, indent_step);
-
-                    put_indent(new_indent);
-
-                    put_literal("\"bytes\": [");
-
-                    if (!val.m_data.m_value.binary->empty())
-                    {
-                        for (auto i = val.m_data.m_value.binary->cbegin();
-                                i != val.m_data.m_value.binary->cend() - 1; ++i)
-                        {
-                            dump_byte(*i);
-                            put_literal(", ");
-                        }
-                        dump_byte(val.m_data.m_value.binary->back());
-                    }
-
-                    put_literal("],\n");
-                    put_indent(new_indent);
-
-                    put_literal("\"subtype\": ");
-                    if (val.m_data.m_value.binary->has_subtype())
-                    {
-                        dump_integer(val.m_data.m_value.binary->subtype());
-                    }
-                    else
-                    {
-                        put_literal("null");
-                    }
-                    put_char('\n');
-                    put_indent(current_indent);
-                    put_char('}');
-                }
-                else
-                {
-                    put_literal("{\"bytes\":[");
-
-                    if (!val.m_data.m_value.binary->empty())
-                    {
-                        for (auto i = val.m_data.m_value.binary->cbegin();
-                                i != val.m_data.m_value.binary->cend() - 1; ++i)
-                        {
-                            dump_byte(*i);
-                            put_char(',');
-                        }
-                        dump_byte(val.m_data.m_value.binary->back());
-                    }
-
-                    put_literal("],\"subtype\":");
-                    if (val.m_data.m_value.binary->has_subtype())
-                    {
-                        dump_integer(val.m_data.m_value.binary->subtype());
-                        put_char('}');
-                    }
-                    else
-                    {
-                        put_literal("null}");
-                    }
-                }
                 return;
             }
 
@@ -627,19 +577,19 @@ class serializer
 
             case value_t::number_integer:
             {
-                dump_integer(val.m_data.m_value.number_integer);
+                dump_signed_value(val.m_data.m_value.number_integer);
                 return;
             }
 
             case value_t::number_unsigned:
             {
-                dump_integer(val.m_data.m_value.number_unsigned);
+                dump_unsigned_value(val.m_data.m_value.number_unsigned);
                 return;
             }
 
             case value_t::number_float:
             {
-                dump_float(val.m_data.m_value.number_float);
+                dump_float_value(val.m_data.m_value.number_float);
                 return;
             }
 
@@ -662,6 +612,107 @@ class serializer
         }
     }
 
+    /// @brief write the string @a s in quotes; kept out of line, so that the
+    /// other scalars do not pay for its register needs (and the other way round)
+    JSON_HEDLEY_NEVER_INLINE void dump_string_value(const string_t& s)
+    {
+#if JSON_DUMP_SHORT_STRINGS
+        if (s.size() <= short_string_max && put_short_quoted(s, "\""))
+        {
+            return;
+        }
+#endif
+        put_char('"');
+        dump_escaped(s);
+        put_char('"');
+    }
+
+    // The numbers, and the rest of what dump_scalar() writes, are left to
+    // functions of their own as well: a single function holding all of them
+    // saves and restores every register any of them needs, on every call. Now
+    // dump_scalar() only dispatches, and each writer pays for what it uses.
+    JSON_HEDLEY_NEVER_INLINE void dump_signed_value(const number_integer_t x)
+    {
+        dump_integer(x);
+    }
+
+    JSON_HEDLEY_NEVER_INLINE void dump_unsigned_value(const number_unsigned_t x)
+    {
+        dump_integer(x);
+    }
+
+    JSON_HEDLEY_NEVER_INLINE void dump_float_value(const number_float_t x)
+    {
+        dump_float(x);
+    }
+
+    JSON_HEDLEY_NEVER_INLINE void dump_binary_value(const std::size_t current_indent, const typename BasicJsonType::binary_t& binary)
+    {
+        if (pretty_print)
+        {
+            put_literal("{\n");
+
+            // variable to hold indentation for the bytes
+            const auto new_indent = next_indent(current_indent, indent_step);
+
+            put_indent(new_indent);
+
+            put_literal("\"bytes\": [");
+
+            if (!binary.empty())
+            {
+                for (auto i = binary.cbegin();
+                        i != binary.cend() - 1; ++i)
+                {
+                    dump_byte(*i);
+                    put_literal(", ");
+                }
+                dump_byte(binary.back());
+            }
+
+            put_literal("],\n");
+            put_indent(new_indent);
+
+            put_literal("\"subtype\": ");
+            if (binary.has_subtype())
+            {
+                dump_integer(binary.subtype());
+            }
+            else
+            {
+                put_literal("null");
+            }
+            put_char('\n');
+            put_indent(current_indent);
+            put_char('}');
+        }
+        else
+        {
+            put_literal("{\"bytes\":[");
+
+            if (!binary.empty())
+            {
+                for (auto i = binary.cbegin();
+                        i != binary.cend() - 1; ++i)
+                {
+                    dump_byte(*i);
+                    put_char(',');
+                }
+                dump_byte(binary.back());
+            }
+
+            put_literal("],\"subtype\":");
+            if (binary.has_subtype())
+            {
+                dump_integer(binary.subtype());
+                put_char('}');
+            }
+            else
+            {
+                put_literal("null}");
+            }
+        }
+    }
 
     /*!
     @brief the indentation level to use for the children of the current value
@@ -678,6 +729,217 @@ class serializer
         return new_indent;
     }
 
+  private:
+    /*!
+    @brief append the string @a s in quotes, followed by @a tail
+
+    The quote, the string and @a tail (the closing quote, possibly with the
+    colon of an object key) are the bulk of what most documents consist of, and
+    most keys and many values are short and plain. Those are handled in one go
+    by put_short_quoted(); everything else takes the general path.
+    */
+    template<std::size_t N>
+    void put_quoted(const string_t& s, const char (&tail)[N]) // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+    {
+#if JSON_DUMP_SHORT_STRINGS
+        if (put_short_quoted(s, tail))
+        {
+            return;
+        }
+#endif
+        put_char('"');
+        dump_escaped(s);
+        put_literal(tail);
+    }
+
+#if JSON_DUMP_SHORT_STRINGS
+    /// the longest string put_short_quoted() takes
+    static constexpr std::size_t short_string_max = JSON_SCAN_VECTOR ? 32 : 16;
+
+    /// the high bit of every byte of @a v that is not printable ASCII or is a
+    /// quote, a backslash, or DEL (zero if the bytes can be copied as they are)
+    static std::uint64_t swar_not_plain(const std::uint64_t v) noexcept
+    {
+        constexpr std::uint64_t ones = 0x0101010101010101ull;
+        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\'
+        return (((q - ones) & ~q) | ((b - ones) & ~b)         // == '"', == '\\'
+                | ((v - 0x2020202020202020ull) & ~v)          // < 0x20
+                | v | (v + ones))                             // >= 0x7F
+               & 0x8080808080808080ull;
+    }
+
+    template<typename WordType>
+    static WordType load_word(const char* p) noexcept
+    {
+        WordType w;
+        std::memcpy(&w, p, sizeof(w));
+        return w;
+    }
+
+    template<typename WordType>
+    static void store_word(char* p, const WordType w) noexcept
+    {
+        std::memcpy(p, &w, sizeof(w));
+    }
+
+    /*!
+    @brief write `"`, @a s and @a tail if @a s is short and needs no escaping
+
+    A string of up to 16 (32 with vector instructions) printable ASCII
+    characters (no quote, backslash, or DEL) is read with two overlapping loads
+    and written with two overlapping stores, instead of scanning it and calling
+    memcpy with a length that is only known at run time. Returns false, having
+    changed nothing, if @a s does not qualify or the write buffer lacks the
+    room.
+    */
+    template<std::size_t N>
+    bool put_short_quoted(const string_t& s, const char (&tail)[N]) // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+    {
+        const std::size_t n = s.size();
+        if (n > short_string_max || write_buffer_pos + n + N > write_buffer.size())
+        {
+            return false;
+        }
+
+        char* d = write_buffer.data() + write_buffer_pos + 1;
+        const char* const p = s.data();
+
+        if (n >= 8)
+        {
+#if JSON_SCAN_VECTOR
+            if (!(n >= 16 ? copy_plain_vectors(d, p, n) : copy_plain_halves(d, p, n)))
+            {
+                return false;
+            }
+#else
+            const auto a = load_word<std::uint64_t>(p);
+            const auto b = load_word<std::uint64_t>(p + n - 8);
+            if ((swar_not_plain(a) | swar_not_plain(b)) != 0)
+            {
+                return false;
+            }
+            store_word(d, a);
+            store_word(d + n - 8, b);
+#endif
+        }
+        else if (n >= 4)
+        {
+            const auto a = load_word<std::uint32_t>(p);
+            const auto b = load_word<std::uint32_t>(p + n - 4);
+            // the bytes above the string are filled with a plain character
+            const std::uint64_t w = a | (static_cast<std::uint64_t>(b) << (8 * (n - 4)))
+                                    | (0x4141414141414141ull << (8 * n));
+            if (swar_not_plain(w) != 0)
+            {
+                return false;
+            }
+            store_word(d, a);
+            store_word(d + n - 4, b);
+        }
+        else if (n >= 2)
+        {
+            const auto a = load_word<std::uint16_t>(p);
+            const auto b = load_word<std::uint16_t>(p + n - 2);
+            const std::uint64_t w = a | (static_cast<std::uint64_t>(b) << (8 * (n - 2)))
+                                    | (0x4141414141414141ull << (8 * n));
+            if (swar_not_plain(w) != 0)
+            {
+                return false;
+            }
+            store_word(d, a);
+            store_word(d + n - 2, b);
+        }
+        else if (n == 1)
+        {
+            const std::uint64_t w = static_cast<std::uint64_t>(static_cast<unsigned char>(p[0])) | (0x4141414141414141ull << 8u);
+            if (swar_not_plain(w) != 0)
+            {
+                return false;
+            }
+            *d = p[0];
+        }
+
+        d[-1] = '"';
+        std::memcpy(d + n, tail, N - 1);
+        write_buffer_pos += n + N;
+        return true;
+    }
+
+#if JSON_SCAN_VECTOR
+    /// copy the 8 to 15 bytes [@a p, @a p + @a n) to @a d with two overlapping
+    /// words, tested together as one vector, see copy_plain_vectors()
+    static bool copy_plain_halves(char* d, const char* p, const std::size_t n) noexcept
+    {
+#if JSON_SCAN_NEON
+        const uint8x8_t lo = vld1_u8(reinterpret_cast<const std::uint8_t*>(p));
+        const uint8x8_t hi = vld1_u8(reinterpret_cast<const std::uint8_t*>(p + n - 8));
+        const uint8x16_t in = vcombine_u8(lo, hi);
+        const uint8x16_t special = vorrq_u8(vorrq_u8(vceqq_u8(in, vdupq_n_u8('"')), vceqq_u8(in, vdupq_n_u8('\\'))),
+                                            vorrq_u8(vcltq_s8(vreinterpretq_s8_u8(in), vdupq_n_s8(0x20)), vceqq_u8(in, vdupq_n_u8(0x7F))));
+        if (vmaxvq_u8(special) != 0)
+        {
+            return false;
+        }
+        vst1_u8(reinterpret_cast<std::uint8_t*>(d), lo);
+        vst1_u8(reinterpret_cast<std::uint8_t*>(d + n - 8), hi);
+#else
+        const __m128i lo = _mm_loadl_epi64(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+        const __m128i hi = _mm_loadl_epi64(static_cast<const __m128i*>(static_cast<const void*>(p + n - 8))); // NOLINT(bugprone-casting-through-void)
+        const __m128i in = _mm_unpacklo_epi64(lo, hi);
+        const __m128i special = _mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(in, _mm_set1_epi8('"')), _mm_cmpeq_epi8(in, _mm_set1_epi8('\\'))),
+                                             _mm_or_si128(_mm_cmplt_epi8(in, _mm_set1_epi8(0x20)), _mm_cmpeq_epi8(in, _mm_set1_epi8(0x7F))));
+        if (_mm_movemask_epi8(special) != 0)
+        {
+            return false;
+        }
+        _mm_storel_epi64(static_cast<__m128i*>(static_cast<void*>(d)), lo); // NOLINT(bugprone-casting-through-void)
+        _mm_storel_epi64(static_cast<__m128i*>(static_cast<void*>(d + n - 8)), hi); // NOLINT(bugprone-casting-through-void)
+#endif
+        return true;
+    }
+
+    /// copy the 16 to 32 bytes [@a p, @a p + @a n) to @a d with two overlapping
+    /// vectors, unless one of them is a quote, a backslash, a control
+    /// character, DEL or not ASCII
+    static bool copy_plain_vectors(char* d, const char* p, const std::size_t n) noexcept
+    {
+#if JSON_SCAN_NEON
+        const uint8x16_t a = vld1q_u8(reinterpret_cast<const std::uint8_t*>(p));
+        const uint8x16_t b = vld1q_u8(reinterpret_cast<const std::uint8_t*>(p + n - 16));
+        const uint8x16_t special = vorrq_u8(vorrq_u8(vorrq_u8(vceqq_u8(a, vdupq_n_u8('"')), vceqq_u8(a, vdupq_n_u8('\\'))),
+                                            vorrq_u8(vceqq_u8(b, vdupq_n_u8('"')), vceqq_u8(b, vdupq_n_u8('\\')))),
+                                            vorrq_u8(vorrq_u8(vcltq_s8(vreinterpretq_s8_u8(a), vdupq_n_s8(0x20)), vcltq_s8(vreinterpretq_s8_u8(b), vdupq_n_s8(0x20))),
+                                                vorrq_u8(vceqq_u8(a, vdupq_n_u8(0x7F)), vceqq_u8(b, vdupq_n_u8(0x7F)))));
+        if (vmaxvq_u8(special) != 0)
+        {
+            return false;
+        }
+        vst1q_u8(reinterpret_cast<std::uint8_t*>(d), a);
+        vst1q_u8(reinterpret_cast<std::uint8_t*>(d + n - 16), b);
+#else
+        const __m128i a = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p))); // NOLINT(bugprone-casting-through-void)
+        const __m128i b = _mm_loadu_si128(static_cast<const __m128i*>(static_cast<const void*>(p + n - 16))); // NOLINT(bugprone-casting-through-void)
+        const __m128i quote = _mm_set1_epi8('"');
+        const __m128i backslash = _mm_set1_epi8('\\');
+        const __m128i space = _mm_set1_epi8(0x20);
+        const __m128i del = _mm_set1_epi8(0x7F);
+        const __m128i special = _mm_or_si128(_mm_or_si128(_mm_or_si128(_mm_cmpeq_epi8(a, quote), _mm_cmpeq_epi8(a, backslash)),
+                                             _mm_or_si128(_mm_cmpeq_epi8(b, quote), _mm_cmpeq_epi8(b, backslash))),
+                                             _mm_or_si128(_mm_or_si128(_mm_cmplt_epi8(a, space), _mm_cmplt_epi8(b, space)),
+                                                 _mm_or_si128(_mm_cmpeq_epi8(a, del), _mm_cmpeq_epi8(b, del))));
+        if (_mm_movemask_epi8(special) != 0)
+        {
+            return false;
+        }
+        _mm_storeu_si128(static_cast<__m128i*>(static_cast<void*>(d)), a); // NOLINT(bugprone-casting-through-void)
+        _mm_storeu_si128(static_cast<__m128i*>(static_cast<void*>(d + n - 16)), b); // NOLINT(bugprone-casting-through-void)
+#endif
+        return true;
+    }
+#endif
+#endif
+
   JSON_PRIVATE_UNLESS_TESTED:
     /*!
     @brief dump escaped string
@@ -690,14 +952,23 @@ class serializer
     @param[in] s  the string to escape
 
     Complexity: Linear in the length of string @a s.
+
+    @note kept out of line: with the short-string attempts in front of it gone
+          from here, compilers would otherwise inline it into @ref put_quoted
+          and then no longer into the loops that call that
     */
-    void dump_escaped(const string_t& s)
+    JSON_HEDLEY_NEVER_INLINE void dump_escaped(const string_t& s)
     {
         // Short strings of printable ASCII - most object keys and many values -
         // are checked byte by byte against a table and then copied in one go.
         // For them, this is cheaper than starting the vector scanner below,
         // whose setup costs more than such a string takes to scan. The same
         // check serves both values of ensure_ascii.
+        //
+        // Where put_short_quoted() exists and takes strings of up to 32 bytes,
+        // the callers have tried it already, and repeating the attempt only
+        // costs time for strings that need escaping or are not ASCII.
+#if !(JSON_DUMP_SHORT_STRINGS && JSON_SCAN_VECTOR)
         if (s.size() <= 32)
         {
             const auto& copyable = ascii_copyable();
@@ -719,6 +990,7 @@ class serializer
                 return;
             }
         }
+#endif
 
         // dispatch once here rather than test the flag inside the loop: it does
         // not change while a string is written, and folding it lets each of the
@@ -796,7 +1068,7 @@ class serializer
                         put_buffer(string_buffer, bytes);
                         bytes = 0;
                     }
-                    put_string(s, i, i + run);
+                    put_run(s, i, run);
                     bytes_after_last_accept = 0;
                     undumped_chars = 0;
                     i += run;
@@ -836,6 +1108,27 @@ class serializer
 
             const auto byte = static_cast<std::uint8_t>(s[i]);
 
+            if (EnsureAscii && state == UTF8_ACCEPT && byte >= 0x80)
+            {
+                // a run of well-formed multi-byte characters is escaped
+                // straight into the write buffer; an ill-formed sequence
+                // ends the run and is left to the byte-at-a-time path
+                if (bytes != 0)
+                {
+                    put_buffer(string_buffer, bytes);
+                    bytes = 0;
+                    bytes_after_last_accept = 0;
+                }
+                const std::size_t escaped = write_u_escapes(reinterpret_cast<const unsigned char*>(s.data()) + i, s.size() - i);
+                if (escaped != 0)
+                {
+                    bytes_after_last_accept = 0;
+                    undumped_chars = 0;
+                    i += escaped - 1;
+                    continue;
+                }
+            }
+
             switch (decode(state, codepoint, byte))
             {
                 case UTF8_ACCEPT:  // decode found a new code point
@@ -1113,6 +1406,21 @@ class serializer
             return;
         }
 
+        // the usual indentation: four words of the indentation character are
+        // stored unconditionally and only the part wanted is claimed, which
+        // spares the call of memset
+        if (JSON_HEDLEY_LIKELY(indent <= 32 && write_buffer_pos + 32 <= write_buffer.size()))
+        {
+            const std::uint64_t word = 0x0101010101010101ull * static_cast<unsigned char>(indent_char);
+            char* const d = write_buffer.data() + write_buffer_pos;
+            std::memcpy(d, &word, sizeof(word));
+            std::memcpy(d + 8, &word, sizeof(word));
+            std::memcpy(d + 16, &word, sizeof(word));
+            std::memcpy(d + 24, &word, sizeof(word));
+            write_buffer_pos += indent;
+            return;
+        }
+
         const std::size_t capacity = write_buffer.size();
 
         // fill whatever room is left in the buffer; this is the whole job
@@ -1146,6 +1454,32 @@ class serializer
         write_buffer_pos = indent;
     }
 
+    /*!
+    @brief append a string literal and then @a indent indentation characters
+
+    The usual line break and indentation go into the buffer with one check of
+    its room and four stores of the indentation, see @ref put_indent.
+    */
+    template<std::size_t N>
+    JSON_HEDLEY_ALWAYS_INLINE void put_literal_indent(const char (&s)[N], const std::size_t indent) // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
+    {
+        constexpr std::size_t length = N - 1;
+        if (JSON_HEDLEY_LIKELY(indent <= 32 && write_buffer_pos + length + 32 <= write_buffer.size()))
+        {
+            const std::uint64_t word = 0x0101010101010101ull * static_cast<unsigned char>(indent_char);
+            char* const d = write_buffer.data() + write_buffer_pos;
+            std::memcpy(d, s, length);
+            std::memcpy(d + length, &word, sizeof(word));
+            std::memcpy(d + length + 8, &word, sizeof(word));
+            std::memcpy(d + length + 16, &word, sizeof(word));
+            std::memcpy(d + length + 24, &word, sizeof(word));
+            write_buffer_pos += length + indent;
+            return;
+        }
+        put_literal(s);
+        put_indent(indent);
+    }
+
     /*!
     @brief append a string literal to the write buffer
 
@@ -1170,6 +1504,28 @@ class serializer
         write_buffer_pos += length;
     }
 
+    /*!
+    @brief append the characters of @a str in [@a start, @a start + @a length)
+
+    A run of up to 16 characters with 16 or more in the string from @a start on
+    and in the write buffer from its end on is copied as a whole block of 16,
+    which spares the call of memcpy with a length known only at run time; the
+    surplus characters in the buffer are overwritten by what follows.
+    */
+    template<typename StringType>
+    void put_run(const StringType& str, const std::size_t start, const std::size_t length)
+    {
+        // a short run is the exception in text without escapes (CJK, accented
+        // Latin), for which this keeps the long path the fast one
+        if (JSON_HEDLEY_UNLIKELY(length <= 16 && start + 16 <= str.size() && write_buffer_pos + 16 <= write_buffer.size()))
+        {
+            std::memcpy(write_buffer.data() + write_buffer_pos, str.data() + start, 16);
+            write_buffer_pos += length;
+            return;
+        }
+        put_string(str, start, start + length);
+    }
+
     /*!
     @brief append the characters of @a str in [@a start, @a end)
 
@@ -1412,6 +1768,75 @@ class serializer
         return escapes;
     }
 
+    /*!
+    @brief escape the well-formed multi-byte characters at the start of @a data
+
+    Writes the "\\uXXXX" escape of each character (two of them for a character
+    above U+FFFF) straight into the write buffer, which is why the caller must
+    have written out what is pending in @ref string_buffer. Stops at the first
+    byte that is below 0x80 or starts an ill-formed or truncated sequence, which
+    the caller handles.
+
+    @return the number of bytes of @a data that have been escaped
+    */
+    JSON_HEDLEY_NEVER_INLINE std::size_t write_u_escapes(const unsigned char* data, std::size_t n)
+    {
+        constexpr const char* nibble_to_hex = "0123456789abcdef";
+        std::size_t i = 0;
+        while (i < n && data[i] >= 0x80)
+        {
+            const std::size_t length = validate_one_utf8(data + i, n - i);
+            if (length == 0)
+            {
+                break;
+            }
+
+            const auto b0 = static_cast<std::uint32_t>(data[i]);
+            const auto b1 = static_cast<std::uint32_t>(data[i + 1]);
+            std::uint32_t codepoint = 0;
+            switch (length)
+            {
+                case 2:
+                    codepoint = ((b0 & 0x1Fu) << 6u) | (b1 & 0x3Fu);
+                    break;
+                case 3:
+                    codepoint = ((b0 & 0x0Fu) << 12u) | ((b1 & 0x3Fu) << 6u) | (static_cast<std::uint32_t>(data[i + 2]) & 0x3Fu);
+                    break;
+                default:
+                    codepoint = ((b0 & 0x07u) << 18u) | ((b1 & 0x3Fu) << 12u) | ((static_cast<std::uint32_t>(data[i + 2]) & 0x3Fu) << 6u) | (static_cast<std::uint32_t>(data[i + 3]) & 0x3Fu);
+                    break;
+            }
+
+            // at most two escapes of six bytes each
+            if (JSON_HEDLEY_UNLIKELY(write_buffer.size() - write_buffer_pos < 12))
+            {
+                flush();
+            }
+            char* d = write_buffer.data() + write_buffer_pos;
+            if (codepoint > 0xFFFFu)
+            {
+                d = put_u_escape(d, static_cast<std::uint16_t>(0xD7C0u + (codepoint >> 10u)), nibble_to_hex);
+                codepoint = 0xDC00u + (codepoint & 0x3FFu);
+            }
+            d = put_u_escape(d, static_cast<std::uint16_t>(codepoint), nibble_to_hex);
+            write_buffer_pos = static_cast<std::size_t>(d - write_buffer.data());
+            i += length;
+        }
+        return i;
+    }
+
+    static char* put_u_escape(char* d, const std::uint16_t codeunit, const char* nibble_to_hex) noexcept
+    {
+        const auto unit = static_cast<std::uint32_t>(codeunit);
+        d[0] = '\\';
+        d[1] = 'u';
+        d[2] = nibble_to_hex[(unit >> 12u) & 0x0Fu];
+        d[3] = nibble_to_hex[(unit >> 8u) & 0x0Fu];
+        d[4] = nibble_to_hex[(unit >> 4u) & 0x0Fu];
+        d[5] = nibble_to_hex[unit & 0x0Fu];
+        return d + 6;
+    }
+
     /*!
      * @brief write a lowercase "\\uXXXX" escape sequence into @a string_buffer
      *
@@ -1769,11 +2194,22 @@ class serializer
     /// the output of the serializer (non-owning; the adapter lives at the call site)
     output_adapter_protocol<char>* o = nullptr;
 
+    /// a character buffer left uninitialized: the buffers below are written
+    /// before they are read (only the part written is ever read), and zeroing
+    /// 1.6 KiB took more than half of what dumping a small value costs (the
+    /// user-provided constructor keeps the member initialization, which
+    /// -Weffc++ asks for, from zeroing them)
+    template<std::size_t N>
+    struct uninitialized_buffer : std::array<char, N>
+    {
+        uninitialized_buffer() noexcept {} // NOLINT(modernize-use-equals-default,hicpp-use-equals-default,cppcoreguidelines-pro-type-member-init,hicpp-member-init): see above
+    };
+
     /// a (hopefully) large enough character buffer
-    std::array<char, 64> number_buffer{{}};
+    uninitialized_buffer<64> number_buffer;
 
     /// string buffer
-    std::array<char, 512> string_buffer{{}};
+    uninitialized_buffer<512> string_buffer;
 
     /// the indentation character
     const char indent_char;
@@ -1793,7 +2229,7 @@ class serializer
     /// buffer collecting output before it is flushed to the output adapter, so
     /// that the many small structural writes become few bulk writes
     static constexpr std::size_t write_buffer_size = 1024;
-    std::array<char, write_buffer_size> write_buffer{{}};
+    uninitialized_buffer<write_buffer_size> write_buffer;
     /// number of valid bytes currently held in @ref write_buffer
     std::size_t write_buffer_pos = 0;
 };

include/nlohmann/json.hpp

@@ -6321,7 +6321,7 @@ public:
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result, error_handler).write_cbor(j);
         return result;
     }
@@ -6331,9 +6331,7 @@ public:
     static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                         const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<std::uint8_t> writer(o, error_handler);
+        binary_writer<std::uint8_t>(o, error_handler).write_cbor(j);
-        writer.write_cbor(j);
-        writer.flush();
     }
 
     /// @brief create a CBOR serialization of a given JSON value
@@ -6341,9 +6339,7 @@ public:
     static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
                         const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<char> writer(o, error_handler);
+        binary_writer<char>(o, error_handler).write_cbor(j);
-        writer.write_cbor(j);
-        writer.flush();
     }
 
     /// @brief create a MessagePack serialization of a given JSON value
@@ -6352,7 +6348,7 @@ public:
             const error_handler_t error_handler = error_handler_t::keep)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result, error_handler).write_msgpack(j);
         return result;
     }
@@ -6362,9 +6358,7 @@ public:
     static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                            const error_handler_t error_handler = error_handler_t::keep)
     {
-        binary_writer<std::uint8_t> writer(o, error_handler);
+        binary_writer<std::uint8_t>(o, error_handler).write_msgpack(j);
-        writer.write_msgpack(j);
-        writer.flush();
     }
 
     /// @brief create a MessagePack serialization of a given JSON value
@@ -6372,9 +6366,7 @@ public:
     static void to_msgpack(const basic_json& j, detail::output_adapter<char> o,
                            const error_handler_t error_handler = error_handler_t::keep)
     {
-        binary_writer<char> writer(o, error_handler);
+        binary_writer<char>(o, error_handler).write_msgpack(j);
-        writer.write_msgpack(j);
-        writer.flush();
     }
 
     /// @brief create a UBJSON serialization of a given JSON value
@@ -6385,7 +6377,7 @@ public:
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result, error_handler).write_ubjson(j, use_size, use_type);
         return result;
     }
@@ -6396,9 +6388,7 @@ public:
                           const bool use_size = false, const bool use_type = false,
                           const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<std::uint8_t> writer(o, error_handler);
+        binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type);
-        writer.write_ubjson(j, use_size, use_type);
-        writer.flush();
     }
 
     /// @brief create a UBJSON serialization of a given JSON value
@@ -6407,9 +6397,7 @@ public:
                           const bool use_size = false, const bool use_type = false,
                           const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<char> writer(o, error_handler);
+        binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type);
-        writer.write_ubjson(j, use_size, use_type);
-        writer.flush();
     }
 
     /// @brief create a BJData serialization of a given JSON value
@@ -6421,7 +6409,7 @@ public:
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
         return result;
     }
@@ -6433,9 +6421,7 @@ public:
                           const bjdata_version_t version = bjdata_version_t::draft2,
                           const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<std::uint8_t> writer(o, error_handler);
+        binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
-        writer.write_ubjson(j, use_size, use_type, true, true, version);
-        writer.flush();
     }
 
     /// @brief create a BJData serialization of a given JSON value
@@ -6445,9 +6431,7 @@ public:
                           const bjdata_version_t version = bjdata_version_t::draft2,
                           const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<char> writer(o, error_handler);
+        binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
-        writer.write_ubjson(j, use_size, use_type, true, true, version);
-        writer.flush();
     }
 
     /// @brief create a BSON serialization of a given JSON value
@@ -6456,7 +6440,7 @@ public:
             const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result, error_handler).write_bson(j);
         return result;
     }
@@ -6466,9 +6450,7 @@ public:
     static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
                         const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<std::uint8_t> writer(o, error_handler);
+        binary_writer<std::uint8_t>(o, error_handler).write_bson(j);
-        writer.write_bson(j);
-        writer.flush();
     }
 
     /// @brief create a BSON serialization of a given JSON value
@@ -6476,9 +6458,7 @@ public:
     static void to_bson(const basic_json& j, detail::output_adapter<char> o,
                         const error_handler_t error_handler = detail::binary_writer_default_error_handler())
     {
-        binary_writer<char> writer(o, error_handler);
+        binary_writer<char>(o, error_handler).write_bson(j);
-        writer.write_bson(j);
-        writer.flush();
     }
 
     /// @brief create a BON8 serialization of a given JSON value
@@ -6486,7 +6466,7 @@ public:
     static std::vector<std::uint8_t> to_bon8(const basic_json& j)
     {
         std::vector<std::uint8_t> result;
-        result.reserve(detail::binary_initial_capacity(j));
+        result.reserve(detail::binary_reserve_hint(j));
         vector_writer(result).write_bon8(j);
         return result;
     }
@@ -6495,18 +6475,14 @@ public:
     /// @sa https://json.nlohmann.me/api/basic_json/to_bon8/
     static void to_bon8(const basic_json& j, detail::output_adapter<std::uint8_t> o)
     {
-        binary_writer<std::uint8_t> writer(o);
+        binary_writer<std::uint8_t>(o).write_bon8(j);
-        writer.write_bon8(j);
-        writer.flush();
     }
 
     /// @brief create a BON8 serialization of a given JSON value
     /// @sa https://json.nlohmann.me/api/basic_json/to_bon8/
     static void to_bon8(const basic_json& j, detail::output_adapter<char> o)
     {
-        binary_writer<char> writer(o);
+        binary_writer<char>(o).write_bon8(j);
-        writer.write_bon8(j);
-        writer.flush();
     }
 
     /// @brief create a JSON value from an input in CBOR format

tests/src/unit-binary_writer_sinks.cpp

@@ -492,275 +492,3 @@ TEST_CASE("binary_reserve_hint never over-reserves")
         CHECK(nlohmann::detail::binary_reserve_hint(json({{"a", 1}, {"b", 2}})) == 5);
     }
 }
-
-namespace
-{
-
-// numbers around every boundary of the integer encodings, and floats of each
-// kind (exact in float, needing double, special values)
-std::vector<json> boundary_numbers()
-{
-    std::vector<json> numbers;
-    for (int k = 0; k < 64; ++k)
-    {
-        const std::uint64_t p = std::uint64_t{1} << k;
-        for (const std::uint64_t d :
-                {
-                    p - 1, p, p + 1
-                })
-        {
-            numbers.emplace_back(d);
-            if (d <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
-            {
-                numbers.emplace_back(static_cast<std::int64_t>(d));
-                numbers.emplace_back(-static_cast<std::int64_t>(d));
-                numbers.emplace_back(-static_cast<std::int64_t>(d) - 1);
-            }
-        }
-    }
-    numbers.emplace_back((std::numeric_limits<std::int64_t>::min)());
-    numbers.emplace_back((std::numeric_limits<std::uint64_t>::max)());
-    for (const double f :
-            {
-                0.0, -0.0, 1.0, -1.0, 0.5, 0.1, 3.25, 1e300, -1e-300, 3.4028234663852886e38, 1e39,
-                std::numeric_limits<double>::infinity(), -std::numeric_limits<double>::infinity(),
-                std::numeric_limits<double>::quiet_NaN()
-            })
-    {
-        numbers.emplace_back(f);
-    }
-    return numbers;
-}
-
-// the concatenation of the encodings of the elements of @a numbers[first, first + count)
-template<typename Single>
-std::vector<std::uint8_t> concat_singles(const std::vector<json>& numbers, const std::size_t first, const std::size_t count, Single single)
-{
-    std::vector<std::uint8_t> bytes;
-    for (std::size_t i = first; i < first + count; ++i)
-    {
-        const auto one = single(numbers[i]);
-        bytes.insert(bytes.end(), one.begin(), one.end());
-    }
-    return bytes;
-}
-
-} // namespace
-
-// Runs of numbers in arrays are encoded straight into space reserved from the
-// sink, by code that is separate from the encoding of a single value. Both have
-// to agree on every number: an array is its head and the encodings of its
-// elements, one after the other.
-TEST_CASE("runs of numbers in arrays are encoded as the numbers one by one")
-{
-    const std::vector<json> numbers = boundary_numbers();
-
-    // arrays of every length that a one-byte head covers, so that runs are as
-    // long as, and longer and shorter than, what fits one reservation
-    for (const std::size_t count :
-            {
-                1u, 2u, 3u, 5u, 14u, 15u, 23u
-            })
-    {
-        for (std::size_t first = 0; first + count <= numbers.size(); first += 7)
-        {
-            const json array(std::vector<json>(numbers.begin() + static_cast<std::ptrdiff_t>(first),
-                                               numbers.begin() + static_cast<std::ptrdiff_t>(first + count)));
-            CAPTURE(array.dump(-1, ' ', false, json::error_handler_t::replace))
-
-            std::vector<std::uint8_t> expected{static_cast<std::uint8_t>(0x80 + count)};
-            auto elements = concat_singles(numbers, first, count, [](const json & j)
-            {
-                return json::to_cbor(j);
-            });
-            expected.insert(expected.end(), elements.begin(), elements.end());
-            CHECK(json::to_cbor(array) == expected);
-
-            expected.assign(1, static_cast<std::uint8_t>(count <= 15 ? 0x90 + count : 0xDC));
-            if (count > 15)
-            {
-                expected.push_back(0);
-                expected.push_back(static_cast<std::uint8_t>(count));
-            }
-            elements = concat_singles(numbers, first, count, [](const json & j)
-            {
-                return json::to_msgpack(j);
-            });
-            expected.insert(expected.end(), elements.begin(), elements.end());
-            CHECK(json::to_msgpack(array) == expected);
-
-            for (const bool bjdata :
-                    {
-                        false, true
-                    })
-            {
-                expected.assign(1, static_cast<std::uint8_t>('['));
-                elements = concat_singles(numbers, first, count, [bjdata](const json & j)
-                {
-                    return bjdata ? json::to_bjdata(j) : json::to_ubjson(j);
-                });
-                expected.insert(expected.end(), elements.begin(), elements.end());
-                expected.push_back(static_cast<std::uint8_t>(']'));
-                CHECK((bjdata ? json::to_bjdata(array) : json::to_ubjson(array)) == expected);
-            }
-
-            // BON8 has no integers above the int64 range
-            bool representable = true;
-            for (std::size_t i = first; i < first + count; ++i)
-            {
-                representable = representable && bon8_representable(numbers[i]);
-            }
-            if (representable)
-            {
-                expected.assign(1, static_cast<std::uint8_t>(count <= 4 ? 0x80 + count : 0x85));
-                elements = concat_singles(numbers, first, count, [](const json & j)
-                {
-                    return json::to_bon8(j);
-                });
-                expected.insert(expected.end(), elements.begin(), elements.end());
-                if (count > 4)
-                {
-                    expected.push_back(0xFE);
-                }
-                CHECK(json::to_bon8(array) == expected);
-            }
-            else
-            {
-                CHECK_THROWS_AS(json::to_bon8(array), json::out_of_range&);
-            }
-        }
-    }
-}
-
-// An array that is written in more than one reservation (more numbers than fit
-// one), and arrays of an index with more digits, round trip for every format.
-TEST_CASE("large arrays and many digits of indices round trip")
-{
-    json array = json::array();
-    for (int i = 0; i < 12000; ++i)
-    {
-        switch (i % 4)
-        {
-            case 0:
-                array.push_back(i);
-                break;
-            case 1:
-                array.push_back(-i);
-                break;
-            case 2:
-                array.push_back(i * 0.25);
-                break;
-            default:
-                array.push_back(i % 8 == 3);
-                break;
-        }
-    }
-    json document = json::object();
-    document["numbers"] = array;
-    document["nested"] = json::array({array, "text", array});
-
-    CHECK(json::from_cbor(json::to_cbor(document)) == document);
-    CHECK(json::from_msgpack(json::to_msgpack(document)) == document);
-    CHECK(json::from_ubjson(json::to_ubjson(document)) == document);
-    CHECK(json::from_ubjson(json::to_ubjson(document, true, true)) == document);
-    CHECK(json::from_bjdata(json::to_bjdata(document)) == document);
-    CHECK(json::from_bson(json::to_bson(document)) == document);
-    CHECK(json::from_bon8(json::to_bon8(document)) == document);
-}
-
-// Strings and keys are written with their head in one reservation up to a
-// length; around that length, and with every kind of head, they must read back.
-TEST_CASE("strings of every head length round trip")
-{
-    json document = json::object();
-    json array = json::array();
-    for (const std::size_t length :
-            {
-                0u, 1u, 2u, 3u, 4u, 7u, 8u, 15u, 16u, 17u, 23u, 24u, 25u, 31u, 32u, 33u, 63u, 127u, 128u, 129u, 200u, 245u, 246u, 247u, 248u, 249u, 250u, 251u, 252u, 253u, 254u, 255u, 256u, 257u, 300u, 1000u, 65535u, 65536u, 70000u
-            })
-    {
-        const std::string text(length, 'x');
-        array.push_back(text);
-        document[std::string(length, 'k')] = text;
-    }
-    document["array"] = array;
-
-    CHECK(json::from_cbor(json::to_cbor(document)) == document);
-    CHECK(json::from_msgpack(json::to_msgpack(document)) == document);
-    CHECK(json::from_ubjson(json::to_ubjson(document)) == document);
-    CHECK(json::from_ubjson(json::to_ubjson(document, true, true)) == document);
-    CHECK(json::from_bjdata(json::to_bjdata(document)) == document);
-    CHECK(json::from_bson(json::to_bson(document)) == document);
-    CHECK(json::from_bon8(json::to_bon8(document)) == document);
-}
-
-// What a write that throws leaves behind in an output adapter is what was written
-// before it, whatever the adapter and however the adapter sink buffers.
-TEST_CASE("a write that throws leaves the same bytes in every kind of output")
-{
-    json array = json::array();
-    for (int i = 0; i < 700; ++i)
-    {
-        array.push_back(i * 1000);
-        array.push_back("text " + std::to_string(i));
-    }
-    array.push_back("bad \xFF byte");
-    json document = json::object();
-    document["first"] = array;
-    document["second"] = 1;
-
-    const auto strict = json::error_handler_t::strict;
-
-    SECTION("cbor")
-    {
-        std::vector<std::uint8_t> as_vector;
-        std::string as_string;
-        std::ostringstream as_stream;
-        CHECK_THROWS_AS(json::to_cbor(document, as_vector, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_cbor(document, as_string, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_cbor(document, as_stream, strict), json::type_error&);
-        CHECK(!as_vector.empty());
-        CHECK(std::string(as_vector.begin(), as_vector.end()) == as_string);
-        CHECK(as_stream.str() == as_string);
-    }
-
-    SECTION("msgpack")
-    {
-        std::vector<std::uint8_t> as_vector;
-        std::string as_string;
-        std::ostringstream as_stream;
-        CHECK_THROWS_AS(json::to_msgpack(document, as_vector, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_msgpack(document, as_string, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_msgpack(document, as_stream, strict), json::type_error&);
-        CHECK(!as_vector.empty());
-        CHECK(std::string(as_vector.begin(), as_vector.end()) == as_string);
-        CHECK(as_stream.str() == as_string);
-    }
-
-    SECTION("ubjson")
-    {
-        std::vector<std::uint8_t> as_vector;
-        std::string as_string;
-        std::ostringstream as_stream;
-        CHECK_THROWS_AS(json::to_ubjson(document, as_vector, false, false, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_ubjson(document, as_string, false, false, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_ubjson(document, as_stream, false, false, strict), json::type_error&);
-        CHECK(!as_vector.empty());
-        CHECK(std::string(as_vector.begin(), as_vector.end()) == as_string);
-        CHECK(as_stream.str() == as_string);
-    }
-
-    SECTION("bson")
-    {
-        // the size pass finds the string before anything is written
-        std::vector<std::uint8_t> as_vector;
-        std::string as_string;
-        std::ostringstream as_stream;
-        CHECK_THROWS_AS(json::to_bson(document, as_vector, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_bson(document, as_string, strict), json::type_error&);
-        CHECK_THROWS_AS(json::to_bson(document, as_stream, strict), json::type_error&);
-        CHECK(as_vector.empty());
-        CHECK(as_string.empty());
-        CHECK(as_stream.str().empty());
-    }
-}

tests/src/unit-custom-number-types.cpp

@@ -285,55 +285,6 @@ TEST_CASE("custom number types: integers beyond 64 bits")
         CHECK(wide_json::to_bjdata(wide_json::array({uint_big, uint_big}), true, true) == expected_bjdata_array);
     }
 
-    SECTION("integers in arrays and objects")
-    {
-        // runs of numbers and scalar object members are encoded by loops of
-        // their own for the number types up to 64 bits; a wider number type
-        // takes the generic path, which checks the range of every integer
-        const wide_json run = wide_json::array({make_int(1), make_int(-3), make_uint(7), wide_json(1.5), int_big, make_int(5)});
-        const wide_json run_negative = wide_json::array({make_int(1), make_int(-3), int_big_negative});
-        const wide_json run_unsigned = wide_json::array({make_uint(1), make_uint(7), uint_big});
-        const wide_json members = wide_json::object({{"a", make_int(1)}, {"b", wide_json(1.5)}, {"c", int_big}});
-
-        const std::vector<wide_json> failing = {run, run_negative, run_unsigned, members, wrap(run), wrap(members)};
-        for (const auto& value : failing)
-        {
-            CHECK_THROWS_AS(_ = wide_json::to_cbor(value), out_of_range&);
-            CHECK_THROWS_AS(_ = wide_json::to_msgpack(value), out_of_range&);
-            CHECK_THROWS_AS(_ = wide_json::to_bson(wrap(value)), out_of_range&);
-            CHECK_THROWS_AS(_ = wide_json::to_bon8(value), out_of_range&);
-        }
-
-        // a failing write leaves no more than the elements before the failing one
-        std::vector<std::uint8_t> out;
-        CHECK_THROWS_AS(wide_json::to_cbor(run, out), out_of_range&);
-        // (the head of the array, 1, -3, 7, and 1.5 as a single-precision float)
-        CHECK(out == std::vector<std::uint8_t>({0x86, 0x01, 0x22, 0x07, 0xFA, 0x3F, 0xC0, 0x00, 0x00}));
-        out.clear();
-        CHECK_THROWS_AS(wide_json::to_bon8(run, out), out_of_range&);
-        CHECK(!out.empty());
-
-        // the same values that fit are written exactly as with 64-bit number types
-        const wide_json fits = wide_json::array({make_int(1), make_int(-3), make_uint(7), wide_json(1.5), make_int(min_int64), make_int(max_int64), make_int(200), make_int(-70000)});
-        const nlohmann::json fits64 = nlohmann::json::array({1, -3, 7, 1.5, (std::numeric_limits<std::int64_t>::min)(), (std::numeric_limits<std::int64_t>::max)(), 200, -70000});
-        CHECK(wide_json::to_cbor(fits) == nlohmann::json::to_cbor(fits64));
-        CHECK(wide_json::to_msgpack(fits) == nlohmann::json::to_msgpack(fits64));
-        CHECK(wide_json::to_ubjson(fits) == nlohmann::json::to_ubjson(fits64));
-        CHECK(wide_json::to_ubjson(fits, true, true) == nlohmann::json::to_ubjson(fits64, true, true));
-        CHECK(wide_json::to_bjdata(fits) == nlohmann::json::to_bjdata(fits64));
-        CHECK(wide_json::to_bjdata(fits, true, true) == nlohmann::json::to_bjdata(fits64, true, true));
-        CHECK(wide_json::to_bon8(fits) == nlohmann::json::to_bon8(fits64));
-        CHECK(wide_json::to_bson(wrap(fits)) == nlohmann::json::to_bson(nlohmann::json::object({{"v", fits64}})));
-
-        const wide_json fit_members = wide_json::object({{"a", make_int(1)}, {"b", make_int(-300)}, {"c", make_uint(max_uint64)}, {"d", wide_json(2.5)}});
-        const nlohmann::json fit_members64 = nlohmann::json::object({{"a", 1}, {"b", -300}, {"c", (std::numeric_limits<std::uint64_t>::max)()}, {"d", 2.5}});
-        CHECK(wide_json::to_cbor(fit_members) == nlohmann::json::to_cbor(fit_members64));
-        CHECK(wide_json::to_msgpack(fit_members) == nlohmann::json::to_msgpack(fit_members64));
-        CHECK(wide_json::to_ubjson(fit_members) == nlohmann::json::to_ubjson(fit_members64));
-        CHECK(wide_json::to_bjdata(fit_members) == nlohmann::json::to_bjdata(fit_members64));
-        CHECK(wide_json::to_bson(fit_members) == nlohmann::json::to_bson(fit_members64));
-    }
-
     SECTION("BJData ND-array")
     {
         // an ND-array element beyond 64 bits does not fit any dtype, so the

tests/src/unit-serialization.cpp

@@ -1580,3 +1580,94 @@ TEST_CASE("invalid UTF-8 at every position is handled like the reference")
         }
     }
 }
+
+TEST_CASE("short strings are written like the reference, as values and as keys")
+{
+    // strings of up to 16 characters (32 with vector instructions) that need no
+    // escaping are written as a whole (together with the quotes and, for a key,
+    // the colon); everything else, including a string that is merely short,
+    // takes the general path.
+    // Every length around the edges of the size classes of the fast path is
+    // combined with each kind of byte that must send a string to the general
+    // path, at each position, and compared with the reference for values and,
+    // via the value, for keys.
+    const std::vector<std::string> specials =
+    {
+        "\"", "\\", "\n", "\x1f", "\x7f", "\xc3\xa9", "\xe2\x82\xac", "\xf0\x9f\x98\x80", "\xff", "\x80", "\xc3"
+    };
+
+    for (std::size_t length = 0; length <= 36; ++length)
+    {
+        const std::string plain(length, 'k');
+        check_dump_against_reference(plain, false);
+
+        for (const auto& special : specials)
+        {
+            for (std::size_t pos = 0; pos <= length; ++pos)
+            {
+                std::string s = plain;
+                s.insert(pos, special);
+                check_dump_against_reference(s, false);
+
+                for (const bool ensure_ascii :
+                        {
+                            false, true
+                        })
+                {
+                    // a key and a value are written alike, in compact and
+                    // in pretty-printed form
+                    const json value = s;
+                    const json object = json::object({{s, 1}});
+                    for (const auto error_handler :
+                            {
+                                json::error_handler_t::replace, json::error_handler_t::keep
+                            })
+                    {
+                        const std::string quoted = value.dump(-1, ' ', ensure_ascii, error_handler);
+                        CHECK(object.dump(-1, ' ', ensure_ascii, error_handler) == "{" + quoted + ":1}");
+                        CHECK(object.dump(2, ' ', ensure_ascii, error_handler) == "{\n  " + quoted + ": 1\n}");
+                    }
+                }
+            }
+        }
+    }
+}
+
+TEST_CASE("runs of multi-byte characters are escaped like the reference under ensure_ascii")
+{
+    // a run of well-formed multi-byte characters is escaped straight into the
+    // write buffer; it has to flush that mid-run, stop at an ASCII character or
+    // an ill-formed sequence and leave those to the general path, and pick up
+    // behind what the general path has pending
+    const std::vector<std::string> characters =
+    {
+        "\xc2\x80", "\xdf\xbf", "\xe0\xa0\x80", "\xe2\x82\xac", "\xed\x9f\xbf", "\xef\xbf\xbf",
+        "\xf0\x90\x80\x80", "\xf0\x9f\x98\x80", "\xf4\x8f\xbf\xbf"
+    };
+    const std::vector<std::string> interruptions =
+    {
+        "", "a", "\n", "\"", "\x7f", "\xff", "\x80", "\xc3", "\xe2\x82", "\xf0\x9f\x98", "\xed\xa0\x80"
+    };
+
+    for (std::size_t shift = 0; shift <= 13; ++shift)
+    {
+        for (const auto& interruption : interruptions)
+        {
+            for (const std::size_t count :
+                    {
+                        std::size_t{1}, std::size_t{2}, std::size_t{85}, std::size_t{200}
+                    })
+            {
+                std::string s(shift, 'x');
+                for (std::size_t i = 0; i < count; ++i)
+                {
+                    s += characters[(i + shift) % characters.size()];
+                }
+                s += interruption;
+                s += characters[shift % characters.size()];
+                s += characters[(shift + 3) % characters.size()];
+                check_dump_against_reference(s, shift < 2);
+            }
+        }
+    }
+}