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Niels Lohmann
d5631dccbd
Parsing from a std::istream read one character at a time through the streambuf, so none of the parser's fast paths applied: it was 1.8 to 2.5 times slower than reading the file into a string and parsing that. input_stream_adapter now exposes the streambuf's get area (gptr() to egptr()) to the lexer as a window. The protected get-area members are reached through member pointers formed in a class derived from std::streambuf, which is ordinary, standard-conforming member access. The lexer scans the window with the same bulk paths as a string, and asks the streambuf for the next character as before when the window is used up. Nothing is read ahead, copied, or put back, so the stream is left exactly where it was left before, with and without JSON_PRECISE_STREAM_POSITION, and a streambuf without a get area is still read one character at a time. The adapter also keeps the current token for error messages as a pointer into the get area, and copies it out only before the get area is refilled, instead of the lexer copying every character. On an Apple M1 Max (Apple Clang, -O3), parsing from an std::ifstream is 1.6 to 2.1 times as fast (twitter.json 4.08 -> 2.30 ms, citm_catalog.json 8.75 -> 4.08 ms), and reading 100,000 small values with operator>> 1.4 (objects) to 4.0 (integers) times as fast. With GCC 13 and libstdc++ on x86-64 Linux, std::ifstream is 1.5 to 2.2 times as fast. Parsing from a stream is now within 11 to 18 % of reading the file into a string first. JSON_DISABLE_STREAM_BULK_SCAN restores reading one character at a time, for streambufs that do not follow the usual get-area contract. The new tests compare every observable result (values, exception messages, stream state, remaining characters) for get areas of 1 to 4096 bytes against a streambuf without a get area, and run again with the macro and with JSON_PRECISE_STREAM_POSITION. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
52 lines
1.5 KiB
C++
52 lines
1.5 KiB
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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// clean up
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#undef JSON_ASSERT
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#undef JSON_INTERNAL_CATCH
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#undef JSON_THROW
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#undef JSON_PRIVATE_UNLESS_TESTED
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#undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
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#undef NLOHMANN_BASIC_JSON_TPL
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#undef JSON_EXPLICIT
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#undef NLOHMANN_CAN_CALL_STD_FUNC_IMPL
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#undef JSON_INLINE_VARIABLE
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#undef JSON_NO_UNIQUE_ADDRESS
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#undef JSON_DISABLE_ENUM_SERIALIZATION
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#undef JSON_DISABLE_TUPLE_REFERENCE_CONVERSION
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#undef JSON_DISABLE_STREAM_BULK_SCAN
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#ifndef JSON_TEST_KEEP_MACROS
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#undef JSON_CATCH
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#undef JSON_TRY
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#undef JSON_HAS_CPP_11
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#undef JSON_HAS_CPP_14
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#undef JSON_HAS_CPP_17
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#undef JSON_HAS_CPP_20
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#undef JSON_HAS_CPP_23
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#undef JSON_HAS_CPP_26
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#undef JSON_HAS_FILESYSTEM
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#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
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#undef JSON_HAS_THREE_WAY_COMPARISON
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#undef JSON_HAS_RANGES
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#undef JSON_HAS_RANGE_VIEW_CONVERSION
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#undef JSON_HAS_STD_FORMAT
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#undef JSON_HAS_STATIC_RTTI
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#undef JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
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#undef JSON_BRACE_INIT_COPY_SEMANTICS
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#undef JSON_PRECISE_STREAM_POSITION
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#undef JSON_STRICT_NUL_HANDLING
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#undef JSON_STRICT_BINARY_UTF8
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#undef JSON_DELETE_DEPRECATED_FUNCTIONS
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#undef JSON_USE_OBJECTS_FOR_ENUM_KEYED_MAPS
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#endif
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#include <nlohmann/thirdparty/hedley/hedley_undef.hpp>
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