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Niels Lohmann
ebfbbf29cb
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>
27 lines
812 B
C++
27 lines
812 B
C++
// __ _____ _____ _____
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// __| | __| | | | JSON for Modern C++
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// | | |__ | | | | | | version 3.12.0
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// |_____|_____|_____|_|___| https://github.com/nlohmann/json
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//
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// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
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// SPDX-License-Identifier: MIT
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#pragma once
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// undefine the macros of detail/view/macro_scope.hpp (at the end of json_view.hpp)
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#undef NLOHMANN_VIEW_HAS_CPP_17
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#undef NLOHMANN_VIEW_LIKELY
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#undef NLOHMANN_VIEW_UNLIKELY
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#undef NLOHMANN_VIEW_ALWAYS_INLINE
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#undef NLOHMANN_VIEW_NOINLINE
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#undef NLOHMANN_VIEW_NODISCARD
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#undef NLOHMANN_VIEW_THROW
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#undef NLOHMANN_VIEW_LITTLE_ENDIAN
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#undef NLOHMANN_VIEW_REPEAT16
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#undef NLOHMANN_VIEW_NEON
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#undef NLOHMANN_VIEW_SSE2
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#undef NLOHMANN_VIEW_SSSE3
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#undef NLOHMANN_VIEW_VECTOR
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#undef NLOHMANN_VIEW_VECTOR_UTF8
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