wt/json

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Niels Lohmann c3b51addbf Scan the strings of json_view with NEON and SSE2

Long runs of string bytes are scanned 16 at a time with NEON (AArch64, with
GCC and Clang) and SSE2 (x86-64): both belong to the baseline instruction
sets. A signed compare with 0x20 finds control characters and non-ASCII
bytes at once. Keys keep 16 table checks before the vector loop (their
lengths repeat from record to record, so the branches predict well);
string values have 8, as their lengths vary more.

Non-ASCII text is validated 16 bytes at a time with the "lookup4" check of
simdjson (J. Keiser and D. Lemire, "Validating UTF-8 In Less Than One
Instruction Per Byte", 2021): with NEON, and on x86-64 with SSSE3 if
JSON_VIEW_USE_SSSE3 is defined (SSSE3 is not part of x86-64, and the code
must not depend on the flags of a translation unit). JSON_VIEW_NO_SIMD
selects the portable code. The vector code sits in
detail/view/simd.hpp; the same input is accepted either way.

json_document::parse, best of 7 runs in separate processes (M1 Max):
poet.json (CJK text) -72%, random.json -25%, twitter.json -22%,
gsoc-2018.json -20%, semanticscholar -19%, github_events -11%,
apache_builds -9.5%, canada/citm -5/-6%; lottie +4%, tree-pretty +2.5%.

Tests: every two-byte sequence and three- and four-byte sequences with
continuation bytes at the edges of their ranges, at every offset around
the vector blocks of keys and values, cut short, and long runs of text
with a damaged byte, against json::accept and json::parse. CMake builds
the parser tests again with JSON_VIEW_NO_SIMD, and on x86-64 with
JSON_VIEW_USE_SSSE3 and -mssse3; the macros are documented.

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

2026-09-30 21:01:55 +02:00

7.8 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_PRECISE_STREAM_POSITION - opt in to leaving an input stream positioned right after a parsed number
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_RANGES - control std::ranges 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_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
JSON_VIEW_NO_SIMD - use only portable code in the parser of json_view.hpp
JSON_VIEW_USE_SSSE3 - validate non-ASCII strings with SSSE3 in the parser of json_view.hpp

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_USE_IMPLICIT_CONVERSIONS - control implicit conversions

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

7.8 KiB Raw Blame History