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json/include/nlohmann/detail/macro_unscope.hpp
T
Niels Lohmann 3e031b06a5 Use standard library helpers where available, with C++11 fallbacks (#5876)
* Use standard library helpers where available, with C++11 fallbacks

Add detail helpers that call the standard library function when the
library provides it (checked with the __cpp_lib_* feature-test macros, so
no new ABI-tag macros) and a C++11 implementation otherwise:

- detail::clamp (std::clamp): by value, so that static constexpr members
  need no out-of-line definition before C++17; used in json_view's dump()
  buffer sizing, where step() can now be a static constexpr member.
- detail::bit_cast (std::bit_cast): replaces dtoa_impl::reinterpret_bits
  and the memcpy bit copies in the number parser, to_chars, the json_view
  serializer, and binary_writer::to_char_type.
- detail::byteswap (std::byteswap): one implementation instead of the
  binary writer's own byte_swap() overloads and the bswap chain in
  to_chars' store_msb_first().
- count_leading_zeros/count_trailing_zeros: two 32-bit _BitScanReverse/
  _BitScanForward calls for MSVC x86/ARM32 instead of the loop, and
  std::countl_zero/countr_zero for compilers without builtins.
- conjunction, disjunction, negation, bool_constant, and uncvref_t map to
  their std counterparts in C++17/C++20.

Builtins and intrinsics stay ahead of the <bit> functions, as MSVC's
std::countl_zero checks for LZCNT at run time unless AVX2 is enabled.

The generated code is unchanged with Clang (C++11/20/23, arm64 and
x86-64) and GCC 16 for parsing, dumping, and the binary formats. The
binary reader keeps its own byte_swap() and the writer its memcpy calls:
the smaller code from detail::byteswap/std::bit_cast there made GCC 16
inline get_number()/write_number() differently, which slowed reading by
10-18 % and writing by about 1 %.

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

* Name the target byte order once (JSON_LITTLE_ENDIAN_TARGET, JSON_BIG_ENDIAN_TARGET)

to_chars.hpp and bit_ops.hpp repeated the long __BYTE_ORDER__/_MSC_VER
conditions; macro_scope.hpp now defines them once (undefined again in
macro_unscope.hpp).

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

* Explain why the serializer growth bound is not a clamp

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

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2026-10-21 20:14:59 +02:00

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// __ _____ _____ _____
// __| | __| | | | JSON for Modern C++
// | | |__ | | | | | | version 3.12.0
// |_____|_____|_____|_|___| https://github.com/nlohmann/json
//
// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
// SPDX-License-Identifier: MIT
#pragma once
// clean up
#undef JSON_ASSERT
#undef JSON_INTERNAL_CATCH
#undef JSON_THROW
#undef JSON_PRIVATE_UNLESS_TESTED
#undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
#undef NLOHMANN_BASIC_JSON_TPL
#undef JSON_EXPLICIT
#undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL
#undef JSON_INLINE_VARIABLE
#undef JSON_NO_UNIQUE_ADDRESS
#undef JSON_DISABLE_ENUM_SERIALIZATION
#undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
#undef JSON_UNLOCKED_FILE_IO
#undef JSON_DTOA_SSE2
#undef JSON_DTOA_NEON
#undef JSON_LITTLE_ENDIAN_TARGET
#undef JSON_BIG_ENDIAN_TARGET
#undef JSON_SCAN_NEON
#undef JSON_SCAN_SSE2
#undef JSON_SCAN_SSSE3
#undef JSON_SCAN_SSSE3_DISPATCH
#undef JSON_SCAN_SSSE3_TARGET
#undef JSON_SCAN_VECTOR
#undef JSON_SCAN_VECTOR_UTF8
#ifndef JSON_TEST_KEEP_MACROS
#undef JSON_CATCH
#undef JSON_TRY
#undef JSON_HAS_CPP_11
#undef JSON_HAS_CPP_14
#undef JSON_HAS_CPP_17
#undef JSON_HAS_CPP_20
#undef JSON_HAS_CPP_23
#undef JSON_HAS_CPP_26
#undef JSON_HAS_FILESYSTEM
#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
#undef JSON_HAS_THREE_WAY_COMPARISON
#undef JSON_HAS_RANGES
#undef JSON_HAS_RANGE_VIEW_CONVERSION
#undef JSON_HAS_STD_FORMAT
#undef JSON_HAS_STATIC_RTTI
#undef JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
#undef JSON_BRACE_INIT_COPY_SEMANTICS
#undef JSON_PRECISE_STREAM_POSITION
#undef JSON_STRICT_NUL_HANDLING
#undef JSON_STRICT_BINARY_UTF8
#undef JSON_DELETE_DEPRECATED_FUNCTIONS
#undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
#undef JSON_DISABLE_STREAM_BULK_SCAN
#undef JSON_DISABLE_UNLOCKED_FILE_IO
#endif
#include <nlohmann/thirdparty/hedley/hedley_undef.hpp>