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Niels Lohmann c6742f9761 Scan strings with SSE2, SSSE3, or NEON

The string fast path found the end of a run of plain characters 8 bytes at
a time (SWAR) and validated non-ASCII text one sequence at a time, calling
validate_one_utf8() out of line for each.

The vector code of json_view's scanner, in the new shared header
detail/input/simd_scan.hpp, now does both 16 bytes at a time: SSE2 finds
the end of a run on x86-64, and the UTF-8 check of Keiser and Lemire runs
with NEON on AArch64 and with SSSE3 on x86-64. SSSE3 is not part of x86-64,
so the check is compiled for it with a function attribute and used when the
CPU has it (cached in a constant-initialized atomic), else the scalar check;
code compiled with -mssse3 skips the CPU check. The first word of a run is
still checked with SWAR (the first four with NEON, where a vector mask
costs more), as most keys and short values end there, and the scalar
helpers are always inlined. On anything else, the scalar code is unchanged.

The new macro JSON_NO_SIMD selects the portable code everywhere, including
the SSE2/NEON digit formatting of the floating-point writer. The lexer tests
now also run with JSON_NO_SIMD and, on x86-64, with -mssse3, and a new test
places every byte that ends a run at each offset across several 16-byte
blocks, after ASCII and after CJK text.

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

2026-10-15 18:37:04 +02:00

8.9 KiB

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Macros

Some aspects of the library can be configured by defining preprocessor macros before including the json.hpp header. See also the macro overview page.

Runtime assertions

JSON_ASSERT(x) - control behavior of runtime assertions

Exceptions

JSON_CATCH_USER(exception)
JSON_THROW_USER(exception)
JSON_TRY_USER - control exceptions
JSON_DIAGNOSTICS - control extended diagnostics
JSON_DIAGNOSTIC_POSITIONS - access positions of elements
JSON_NOEXCEPTION - switch off exceptions

Parsing

JSON_DISABLE_STREAM_BULK_SCAN - read a std::istream one character at a time instead of scanning its stream buffer in bulk
JSON_DISABLE_UNLOCKED_FILE_IO - read a FILE* with std::fgetc instead of locking it once and using the unlocked stdio functions
JSON_PRECISE_STREAM_POSITION - opt in to leaving an input stream positioned right after a parsed number
JSON_STRICT_BINARY_UTF8 - opt in to checking strings for valid UTF-8 in the CBOR, UBJSON, BJData, and BSON writers
JSON_STRICT_NUL_HANDLING - opt in to rejecting a NUL byte in the input instead of treating it as end of input

Language support

JSON_HAS_CPP_11
JSON_HAS_CPP_14
JSON_HAS_CPP_17
JSON_HAS_CPP_20 - set supported C++ standard
JSON_HAS_FILESYSTEM
JSON_HAS_EXPERIMENTAL_FILESYSTEM - control std::filesystem support
JSON_HAS_RANGE_VIEW_CONVERSION - control construction from std::ranges views
JSON_HAS_RANGES - control std::ranges support
JSON_HAS_STATIC_RTTI - control RTTI (run time type information) support
JSON_HAS_STD_FORMAT - control std::format/std::formatter support
JSON_HAS_THREE_WAY_COMPARISON - control 3-way comparison support
JSON_NO_AUTOMATIC_UDLS - do not include the user-defined string literals (UDLs) automatically
JSON_NO_IO - switch off functions relying on certain C++ I/O headers
JSON_NO_SIMD - use only portable code instead of vector instructions (SSE2, SSSE3, NEON)
JSON_NO_THREAD_LOCAL - switch off the use of thread_local storage
JSON_SKIP_UNSUPPORTED_COMPILER_CHECK - do not warn about unsupported compilers
JSON_USE_GLOBAL_UDLS - place user-defined string literals (UDLs) into the global namespace
JSON_USE_SIMDUTF - use the simdutf library to accelerate UTF-8 validation

Library version

JSON_SKIP_LIBRARY_VERSION_CHECK - skip library version check
NLOHMANN_JSON_VERSION_MAJOR
NLOHMANN_JSON_VERSION_MINOR
NLOHMANN_JSON_VERSION_PATCH - library version information

Library namespace

NLOHMANN_JSON_NAMESPACE - full name of the nlohmann namespace
NLOHMANN_JSON_NAMESPACE_BEGIN
NLOHMANN_JSON_NAMESPACE_END - open and close the library namespace
NLOHMANN_JSON_NAMESPACE_NO_VERSION - disable the version component of the inline namespace

Type conversions

JSON_BRACE_INIT_COPY_SEMANTICS - opt in to copy/move semantics for single-element brace initialization
JSON_DISABLE_ENUM_SERIALIZATION - switch off default serialization/deserialization functions for enums
JSON_DISABLE_TUPLE_REFERENCE_CONVERSION - switch off conversion from a one-element tuple of a JSON reference
JSON_USE_IMPLICIT_CONVERSIONS - control implicit conversions
JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS - opt in to storing maps with enum keys as objects

Deprecated functions

JSON_DELETE_DEPRECATED_FUNCTIONS - opt in to deleting the deprecated functions ahead of their removal in version 4.0.0

Comparison behavior

JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON - control comparison of discarded values

Serialization/deserialization macros

Enums

NLOHMANN_JSON_SERIALIZE_ENUM - serialize/deserialize an enum
NLOHMANN_JSON_SERIALIZE_ENUM_STRICT - serialize/deserialize an enum with exceptions

Classes and structs

NLOHMANN_DEFINE_TYPE_INTRUSIVE - serialize/deserialize a non-derived class with private members
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class with private members; uses default values
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class with private members
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE - serialize/deserialize a non-derived class
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a non-derived class; uses default values
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a non-derived class
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE - serialize/deserialize a derived class with private members
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class with private members; uses default values
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class with private members
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE - serialize/deserialize a derived class
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT - serialize/deserialize a derived class; uses default values
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE - serialize a derived class
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses custom names
NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class with private members; uses default values; uses custom names
NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class with private members; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a non-derived class; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a non-derived class; uses default values; uses custom names
NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a non-derived class; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class with private members; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class with private members; uses default values; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class with private members; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_NAMES - serialize/deserialize a derived class; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT_WITH_NAMES - serialize/deserialize a derived class; uses default values; uses custom names
NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE_WITH_NAMES - serialize a derived class; uses custom names

8.9 KiB Raw Blame History