b0db8653b6
float, double, and long double where it is IEEE-754 binary64 (MSVC, Apple arm64) are now converted by the library itself, correctly rounded and independent of the locale and of the C and C++ libraries: - The token is split into sign, significand w (at most 19 digits), and decimal exponent q, using the positions of the decimal point and the exponent that the scanners already recorded, so no character is classified again. - Clinger's fast path where w and 10^|q| are exact. - Eisel-Lemire otherwise, now templated for binary32 and binary64. - For tokens with more than 19 digits whose w and w + 1 round differently, an exact big-integer comparison with the midpoint between the two candidates (the digit comparison of fast_float, simplified). This replaces the separate token walks of Clinger's fast path and of Eisel-Lemire, the significant-digit gate that avoided the former, and, for float and double, std::from_chars and the locale-aware strtod. std::from_chars and strtold remain only for other long double formats (x87, binary128, double-double) and for types that are not IEEE-754. Values are bit-identical to before wherever the previous conversion was correctly rounded; tokens converted in a locale with a multi-byte decimal point are now also exact. Overflow still gives out_of_range.406, underflow a signed zero. convert_float() is the entry point for other parsers of JSON text: it converts like the lexer, without allocation for binary32/binary64. Tests: exact-bit tests for double and float (ties, subnormal and overflow boundaries, huge exponents, more digits than any midpoint), Eisel-Lemire for binary32, the round trips of 200,000 doubles and 100,000 floats without declines, 508 generated hard cases with the expected bits of both formats (float_hard_cases.hpp) through the converter and both scanners, and JSON-level overflow/underflow checks for double and float. The locale tests now check the values in a locale with a multi-byte decimal point. Docs: the statements that parsing uses strtod/strtof/strtold; the fast_float credit now names the digit comparison. Signed-off-by: Niels Lohmann <mail@nlohmann.me>
2.4 KiB
License
The class is licensed under the MIT License:
Copyright © 2013-2026 Niels Lohmann
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
The class contains the UTF-8 Decoder from Bjoern Hoehrmann which is licensed under the MIT License (see above). Copyright © 2008-2009 Björn Hoehrmann bjoern@hoehrmann.de
The class contains a slightly modified version of the Grisu2 algorithm from Florian Loitsch which is licensed under the MIT License (see above). Copyright © 2009 Florian Loitsch
The class contains a copy of Hedley from Evan Nemerson which is licensed as CC0-1.0.
The class contains an adapted version of the Eisel-Lemire algorithm, its table of powers of five, and its digit comparison for long numbers from fast_float by Daniel Lemire and contributors, which is available under the MIT License (used here), the Apache 2.0 License, and the Boost Software License. Copyright © 2021 The fast_float authors