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bf6b5b4719
The parser records where the integer digits, the fraction digits, and the exponent of a float token are. For doubles with at most 19 digits, the value is now read from that layout: the digits eight at a time, without scanning the token, and rounded with Clinger's fast path where both operands are exact, else with the Eisel-Lemire algorithm (which needs no fallback for up to 19 digits). Both round correctly, so the values are those of parse(); other tokens and types keep the library's conversion. get<double>(), materialize(), dump(), and comparisons use it. Traversing canada.json (111,000 floats, every number converted): 0.53 -> 0.86 GB/s. Tests add tokens around the limits (19 and 20 digits, 2^53, 10^22) to the bit-for-bit comparison with parse(). Signed-off-by: Niels Lohmann <mail@nlohmann.me>
132 lines
3.9 KiB
C++
132 lines
3.9 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 <cstdint> // int64_t, uint8_t
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#include <string> // string
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#include <vector> // vector
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#include <nlohmann/json.hpp>
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#include <nlohmann/detail/view/document_data.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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#include <nlohmann/detail/view/number.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 basic_json value of the subtree at n
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The subtree is replayed into the SAX handler that parse() uses to build its
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values, so the result is the value parse() would produce: duplicate keys keep
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the last value, and with JSON_DIAGNOSTICS the parent pointers are set. It is
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iterative, so the nesting depth is limited by memory only, as for parse().
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Without a lexer the handler records no source positions
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(JSON_DIAGNOSTIC_POSITIONS).
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*/
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template<typename BasicJsonType>
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BasicJsonType materialize(const document_data& d, const node* n)
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{
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using string_t = typename BasicJsonType::string_t;
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using sax_t = json_sax_dom_parser<BasicJsonType, iterator_input_adapter<const char*>>;
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BasicJsonType result;
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sax_t sax(result, true);
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const string_t no_token{};
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// the ends of the open containers, and whether they are objects
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std::vector<std::pair<const node*, bool>> open;
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for (;;)
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{
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switch (static_cast<value_t>(n->kind))
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{
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case value_t::object:
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case value_t::array:
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{
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const bool object = n->kind == static_cast<std::uint8_t>(value_t::object);
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if (object)
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{
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sax.start_object(n->len);
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}
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else
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{
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sax.start_array(n->len);
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}
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open.emplace_back(document_data::child_end(n), object);
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n = document_data::first_child(n);
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break;
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}
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case value_t::string:
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{
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string_t s(d.str(*n), n->len);
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sax.string(s);
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++n;
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break;
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}
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case value_t::number_integer:
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sax.number_integer(static_cast<typename BasicJsonType::number_integer_t>(static_cast<std::int64_t>(integer_bits(*n))));
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++n;
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break;
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case value_t::number_unsigned:
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sax.number_unsigned(static_cast<typename BasicJsonType::number_unsigned_t>(integer_bits(*n)));
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++n;
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break;
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case value_t::number_float:
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sax.number_float(float_value<typename BasicJsonType::number_float_t>(d, *n), no_token);
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++n;
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break;
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case value_t::boolean:
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sax.boolean((n->flags & node_flags::is_true) != 0);
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++n;
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break;
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case value_t::null:
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case value_t::binary:
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case value_t::discarded:
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default:
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sax.null();
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++n;
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break;
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}
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for (;;)
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{
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if (open.empty())
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{
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return result;
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}
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if (n != open.back().first)
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{
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break;
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}
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if (open.back().second)
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{
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sax.end_object();
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}
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else
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{
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sax.end_array();
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}
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open.pop_back();
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}
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if (open.back().second)
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{
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// the key of the next member
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string_t key(d.str(*n), n->len);
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sax.key(key);
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++n;
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}
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}
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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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