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Niels Lohmann
4303ba674d
Add json_document and json_view, a read-only, zero-copy index of a JSON text, as the first public slice of the zero-copy view (#5295). A parse produces a flat array of 16-byte nodes in document order, one per value and one per object key. Strings stay in the source text; escaped strings are decoded into an arena. Integers are converted while their digits are in the cache; floats keep only their digit layout and are converted on read. Containers store the size of their subtree, so a reader can step over one in constant time. A document makes a handful of allocations, however many values it has. The parser accepts exactly what json::parse accepts, with every combination of ignore_comments and ignore_trailing_commas, with and without a trailing NUL, and under JSON_STRICT_NUL_HANDLING. It is portable C++11 and does not depend on byte order. basic_json_document adds parse, parse_copy, accept, read (reuses a document's memory), root, is_discarded, source, owns_source, node_count, memory_usage, and shrink_to_fit. basic_json_view adds type, the is_* queries, operator bool, size, empty, materialize, and source_offset. A parse error throws the same exception basic_json::parse would throw for the same input, message and position included. detail::abi_config keeps JSON_STRICT_NUL_HANDLING and JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON readable after json.hpp undefines them, in the ABI namespace so they always match the basic_json in use. A NUL byte that ends a // comment is the end of the input, as in parse() since #5696. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
68 lines
2.0 KiB
C++
68 lines
2.0 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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#include <cstddef> // size_t
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#include <string> // string
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/macro_scope.hpp>
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#include <nlohmann/detail/view/node.hpp>
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NLOHMANN_JSON_NAMESPACE_BEGIN
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namespace detail
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{
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namespace view
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{
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/*!
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@brief the value of the float token of a node, as parse() converts it
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Uses the lexer's conversion (detail::convert_float), so that the values are
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bit-identical to parse(): float and double are converted without allocation
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and independent of the locale. The digit layout recorded while parsing locates
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the decimal point and the exponent without scanning the token.
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*/
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template<typename FloatType>
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NLOHMANN_VIEW_NOINLINE FloatType float_value(const char* first, const node& n)
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{
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const char* const last = first + n.len;
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const std::size_t neg = first[0] == '-' ? 1 : 0;
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const std::size_t int_digits = n.extra & 0xFFu;
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const std::size_t frac_digits = n.extra >> 8u;
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std::size_t dot = std::string::npos;
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std::size_t mantissa_end = n.len;
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if (int_digits != 255 && frac_digits != 255)
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{
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dot = frac_digits != 0 ? neg + int_digits : std::string::npos;
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mantissa_end = neg + int_digits + (frac_digits != 0 ? 1 + frac_digits : 0);
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}
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else
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{
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// more digits than the layout records: locate them
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for (std::size_t i = 0; i < n.len; ++i)
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{
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if (first[i] == '.')
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{
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dot = i;
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}
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else if (first[i] == 'e' || first[i] == 'E')
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{
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mantissa_end = i;
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break;
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}
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}
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}
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return convert_float<FloatType>(first, last, dot, mantissa_end);
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}
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} // namespace view
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} // namespace detail
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NLOHMANN_JSON_NAMESPACE_END
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