1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
10#define _LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
11
12// These headers are in the shared LLVM-libc header library.
13#include "shared/fp_bits.h"
14#include "shared/str_to_float.h"
15#include "shared/str_to_integer.h"
16
17#include <__assert>
18#include <__config>
19#include <cctype>
20#include <charconv>
21#include <concepts>
22#include <limits>
23
24// Included for the _Floating_type_traits class
25#include "to_chars_floating_point.h"
26
27_LIBCPP_BEGIN_NAMESPACE_STD
28
29// Parses an infinity string.
30// Valid strings are case insensitive and contain INF or INFINITY.
31//
32// - __first is the first argument to std::from_chars. When the string is invalid
33// this value is returned as ptr in the result.
34// - __last is the last argument of std::from_chars.
35// - __value is the value argument of std::from_chars,
36// - __ptr is the current position is the input string. This is points beyond
37// the initial I character.
38// - __negative whether a valid string represents -inf or +inf.
39template <floating_point _Fp>
40__from_chars_result<_Fp>
41__from_chars_floating_point_inf(const char* const __first, const char* __last, const char* __ptr, bool __negative) {
42 if (__last - __ptr < 2) [[unlikely]]
43 return {_Fp{0}, 0, errc::invalid_argument};
44
45 if (std::tolower(c: __ptr[0]) != 'n' || std::tolower(c: __ptr[1]) != 'f') [[unlikely]]
46 return {_Fp{0}, 0, errc::invalid_argument};
47
48 __ptr += 2;
49
50 // At this point the result is valid and contains INF.
51 // When the remaining part contains INITY this will be consumed. Otherwise
52 // only INF is consumed. For example INFINITZ will consume INF and ignore
53 // INITZ.
54
55 if (__last - __ptr >= 5 //
56 && std::tolower(c: __ptr[0]) == 'i' //
57 && std::tolower(c: __ptr[1]) == 'n' //
58 && std::tolower(c: __ptr[2]) == 'i' //
59 && std::tolower(c: __ptr[3]) == 't' //
60 && std::tolower(c: __ptr[4]) == 'y')
61 __ptr += 5;
62
63 if constexpr (numeric_limits<_Fp>::has_infinity) {
64 if (__negative)
65 return {-std::numeric_limits<_Fp>::infinity(), __ptr - __first, std::errc{}};
66
67 return {std::numeric_limits<_Fp>::infinity(), __ptr - __first, std::errc{}};
68 } else {
69 return {_Fp{0}, __ptr - __first, errc::result_out_of_range};
70 }
71}
72
73// Parses a nan string.
74// Valid strings are case insensitive and contain INF or INFINITY.
75//
76// - __first is the first argument to std::from_chars. When the string is invalid
77// this value is returned as ptr in the result.
78// - __last is the last argument of std::from_chars.
79// - __value is the value argument of std::from_chars,
80// - __ptr is the current position is the input string. This is points beyond
81// the initial N character.
82// - __negative whether a valid string represents -nan or +nan.
83template <floating_point _Fp>
84__from_chars_result<_Fp>
85__from_chars_floating_point_nan(const char* const __first, const char* __last, const char* __ptr, bool __negative) {
86 if (__last - __ptr < 2) [[unlikely]]
87 return {_Fp{0}, 0, errc::invalid_argument};
88
89 if (std::tolower(c: __ptr[0]) != 'a' || std::tolower(c: __ptr[1]) != 'n') [[unlikely]]
90 return {_Fp{0}, 0, errc::invalid_argument};
91
92 __ptr += 2;
93
94 // At this point the result is valid and contains NAN. When the remaining
95 // part contains ( n-char-sequence_opt ) this will be consumed. Otherwise
96 // only NAN is consumed. For example NAN(abcd will consume NAN and ignore
97 // (abcd.
98 if (__last - __ptr >= 2 && __ptr[0] == '(') {
99 size_t __offset = 1;
100 do {
101 if (__ptr[__offset] == ')') {
102 __ptr += __offset + 1;
103 break;
104 }
105 if (__ptr[__offset] != '_' && !std::isalnum(c: __ptr[__offset]))
106 break;
107 ++__offset;
108 } while (__ptr + __offset != __last);
109 }
110
111 if (__negative)
112 return {-std::numeric_limits<_Fp>::quiet_NaN(), __ptr - __first, std::errc{}};
113
114 return {std::numeric_limits<_Fp>::quiet_NaN(), __ptr - __first, std::errc{}};
115}
116
117template <class _Tp>
118struct __fractional_constant_result {
119 size_t __offset{size_t(-1)};
120 _Tp __mantissa{0};
121 int __exponent{0};
122 bool __truncated{false};
123 bool __is_valid{false};
124};
125
126// Parses the hex constant part of the hexadecimal floating-point value.
127// - input start of buffer given to from_chars
128// - __n the number of elements in the buffer
129// - __offset where to start parsing. The input can have an optional sign, the
130// offset starts after this sign.
131template <class _Tp>
132__fractional_constant_result<_Tp> __parse_fractional_hex_constant(const char* __input, size_t __n, size_t __offset) {
133 __fractional_constant_result<_Tp> __result;
134
135 const _Tp __mantissa_truncate_threshold = numeric_limits<_Tp>::max() / 16;
136 bool __fraction = false;
137 for (; __offset < __n; ++__offset) {
138 if (std::isxdigit(c: __input[__offset])) {
139 __result.__is_valid = true;
140
141 uint32_t __digit = __input[__offset] - '0';
142 switch (std::tolower(c: __input[__offset])) {
143 case 'a':
144 __digit = 10;
145 break;
146 case 'b':
147 __digit = 11;
148 break;
149 case 'c':
150 __digit = 12;
151 break;
152 case 'd':
153 __digit = 13;
154 break;
155 case 'e':
156 __digit = 14;
157 break;
158 case 'f':
159 __digit = 15;
160 break;
161 }
162
163 if (__result.__mantissa < __mantissa_truncate_threshold) {
164 __result.__mantissa = (__result.__mantissa * 16) + __digit;
165 if (__fraction)
166 __result.__exponent -= 4;
167 } else {
168 if (__digit > 0)
169 __result.__truncated = true;
170 if (!__fraction)
171 __result.__exponent += 4;
172 }
173 } else if (__input[__offset] == '.') {
174 if (__fraction)
175 break; // this means that __input[__offset] points to a second decimal point, ending the number.
176
177 __fraction = true;
178 } else
179 break;
180 }
181
182 __result.__offset = __offset;
183 return __result;
184}
185
186struct __exponent_result {
187 size_t __offset{size_t(-1)};
188 int __value{0};
189 bool __present{false};
190};
191
192// When the exponent is not present the result of the struct contains
193// __offset, 0, false. This allows using the results unconditionally, the
194// __present is important for the scientific notation, where the value is
195// mandatory.
196__exponent_result __parse_exponent(const char* __input, size_t __n, size_t __offset, char __marker) {
197 if (__offset + 1 < __n && // an exponent always needs at least one digit.
198 std::tolower(c: __input[__offset]) == __marker && //
199 !std::isspace(c: __input[__offset + 1]) // leading whitespace is not allowed.
200 ) {
201 ++__offset;
202 LIBC_NAMESPACE::shared::StrToNumResult<int32_t> __e =
203 LIBC_NAMESPACE::shared::strtointeger<int32_t>(src: __input + __offset, base: 10, src_len: __n - __offset);
204 // __result.error contains the errno value, 0 or ERANGE these are not interesting.
205 // If the number of characters parsed is 0 it means there was no number.
206 if (__e.parsed_len != 0)
207 return {__offset + __e.parsed_len, __e.value, true};
208 else
209 --__offset; // the assumption of a valid exponent was not true, undo eating the exponent character.
210 }
211
212 return {__offset, 0, false};
213}
214
215// Here we do this operation as int64 to avoid overflow.
216int32_t __merge_exponents(int64_t __fractional, int64_t __exponent, int __max_biased_exponent) {
217 int64_t __sum = __fractional + __exponent;
218
219 if (__sum > __max_biased_exponent)
220 return __max_biased_exponent;
221
222 if (__sum < -__max_biased_exponent)
223 return -__max_biased_exponent;
224
225 return __sum;
226}
227
228template <class _Fp, class _Tp>
229__from_chars_result<_Fp>
230__calculate_result(_Tp __mantissa, int __exponent, bool __negative, __from_chars_result<_Fp> __result) {
231 auto __r = LIBC_NAMESPACE::shared::FPBits<_Fp>();
232 __r.set_mantissa(__mantissa);
233 __r.set_biased_exponent(__exponent);
234
235 // C17 7.12.1/6
236 // The result underflows if the magnitude of the mathematical result is so
237 // small that the mathematical result cannot be represented, without
238 // extraordinary roundoff error, in an object of the specified type.237) If
239 // the result underflows, the function returns an implementation-defined
240 // value whose magnitude is no greater than the smallest normalized positive
241 // number in the specified type; if the integer expression math_errhandling
242 // & MATH_ERRNO is nonzero, whether errno acquires the value ERANGE is
243 // implementation-defined; if the integer expression math_errhandling &
244 // MATH_ERREXCEPT is nonzero, whether the "underflow" floating-point
245 // exception is raised is implementation-defined.
246 //
247 // LLVM-LIBC sets ERAGNE for subnormal values
248 //
249 // [charconv.from.chars]/1
250 // ... If the parsed value is not in the range representable by the type of
251 // value, value is unmodified and the member ec of the return value is
252 // equal to errc::result_out_of_range. ...
253 //
254 // Undo the ERANGE for subnormal values.
255 if (__result.__ec == errc::result_out_of_range && __r.is_subnormal() && !__r.is_zero())
256 __result.__ec = errc{};
257
258 if (__negative)
259 __result.__value = -__r.get_val();
260 else
261 __result.__value = __r.get_val();
262
263 return __result;
264}
265
266// Implements from_chars for decimal floating-point values.
267// __first forwarded from from_chars
268// __last forwarded from from_chars
269// __value forwarded from from_chars
270// __fmt forwarded from from_chars
271// __ptr the start of the buffer to parse. This is after the optional sign character.
272// __negative should __value be set to a negative value?
273//
274// This function and __from_chars_floating_point_decimal are similar. However
275// the similar parts are all in helper functions. So the amount of code
276// duplication is minimal.
277template <floating_point _Fp>
278__from_chars_result<_Fp>
279__from_chars_floating_point_hex(const char* const __first, const char* __last, const char* __ptr, bool __negative) {
280 size_t __n = __last - __first;
281 ptrdiff_t __offset = __ptr - __first;
282
283 auto __fractional =
284 std::__parse_fractional_hex_constant<typename _Floating_type_traits<_Fp>::_Uint_type>(__first, __n, __offset);
285 if (!__fractional.__is_valid)
286 return {_Fp{0}, 0, errc::invalid_argument};
287
288 auto __parsed_exponent = std::__parse_exponent(input: __first, __n, offset: __fractional.__offset, marker: 'p');
289 __offset = __parsed_exponent.__offset;
290 int __exponent = std::__merge_exponents(
291 fractional: __fractional.__exponent, exponent: __parsed_exponent.__value, LIBC_NAMESPACE::shared::FPBits<_Fp>::MAX_BIASED_EXPONENT);
292
293 __from_chars_result<_Fp> __result{_Fp{0}, __offset, {}};
294 LIBC_NAMESPACE::shared::ExpandedFloat<_Fp> __expanded_float = {0, 0};
295 if (__fractional.__mantissa != 0) {
296 auto __temp = LIBC_NAMESPACE::shared::binary_exp_to_float<_Fp>(
297 {__fractional.__mantissa, __exponent},
298 __fractional.__truncated,
299 LIBC_NAMESPACE::shared::RoundDirection::Nearest);
300 __expanded_float = __temp.num;
301 if (__temp.error == ERANGE) {
302 __result.__ec = errc::result_out_of_range;
303 }
304 }
305
306 return std::__calculate_result<_Fp>(__expanded_float.mantissa, __expanded_float.exponent, __negative, __result);
307}
308
309// Parses the hex constant part of the decimal float value.
310// - input start of buffer given to from_chars
311// - __n the number of elements in the buffer
312// - __offset where to start parsing. The input can have an optional sign, the
313// offset starts after this sign.
314template <class _Tp>
315__fractional_constant_result<_Tp>
316__parse_fractional_decimal_constant(const char* __input, ptrdiff_t __n, ptrdiff_t __offset) {
317 __fractional_constant_result<_Tp> __result;
318
319 const _Tp __mantissa_truncate_threshold = numeric_limits<_Tp>::max() / 10;
320 bool __fraction = false;
321 for (; __offset < __n; ++__offset) {
322 if (std::isdigit(c: __input[__offset])) {
323 __result.__is_valid = true;
324
325 uint32_t __digit = __input[__offset] - '0';
326 if (__result.__mantissa < __mantissa_truncate_threshold) {
327 __result.__mantissa = (__result.__mantissa * 10) + __digit;
328 if (__fraction)
329 --__result.__exponent;
330 } else {
331 if (__digit > 0)
332 __result.__truncated = true;
333 if (!__fraction)
334 ++__result.__exponent;
335 }
336 } else if (__input[__offset] == '.') {
337 if (__fraction)
338 break; // this means that __input[__offset] points to a second decimal point, ending the number.
339
340 __fraction = true;
341 } else
342 break;
343 }
344
345 __result.__offset = __offset;
346 return __result;
347}
348
349// Implements from_chars for decimal floating-point values.
350// __first forwarded from from_chars
351// __last forwarded from from_chars
352// __value forwarded from from_chars
353// __fmt forwarded from from_chars
354// __ptr the start of the buffer to parse. This is after the optional sign character.
355// __negative should __value be set to a negative value?
356template <floating_point _Fp>
357__from_chars_result<_Fp> __from_chars_floating_point_decimal(
358 const char* const __first, const char* __last, chars_format __fmt, const char* __ptr, bool __negative) {
359 ptrdiff_t __n = __last - __first;
360 ptrdiff_t __offset = __ptr - __first;
361
362 auto __fractional =
363 std::__parse_fractional_decimal_constant<typename _Floating_type_traits<_Fp>::_Uint_type>(__first, __n, __offset);
364 if (!__fractional.__is_valid)
365 return {_Fp{0}, 0, errc::invalid_argument};
366
367 __offset = __fractional.__offset;
368
369 // LWG3456 Pattern used by std::from_chars is underspecified
370 // This changes fixed to ignore a possible exponent instead of making its
371 // existance an error.
372 int __exponent;
373 if (__fmt == chars_format::fixed) {
374 __exponent =
375 std::__merge_exponents(fractional: __fractional.__exponent, exponent: 0, LIBC_NAMESPACE::shared::FPBits<_Fp>::MAX_BIASED_EXPONENT);
376 } else {
377 auto __parsed_exponent = std::__parse_exponent(input: __first, __n, __offset, marker: 'e');
378 if (__fmt == chars_format::scientific && !__parsed_exponent.__present) {
379 // [charconv.from.chars]/6.2 if fmt has chars_format::scientific set but not chars_format::fixed,
380 // the otherwise optional exponent part shall appear;
381 return {_Fp{0}, 0, errc::invalid_argument};
382 }
383
384 __offset = __parsed_exponent.__offset;
385 __exponent = std::__merge_exponents(
386 fractional: __fractional.__exponent, exponent: __parsed_exponent.__value, LIBC_NAMESPACE::shared::FPBits<_Fp>::MAX_BIASED_EXPONENT);
387 }
388
389 __from_chars_result<_Fp> __result{_Fp{0}, __offset, {}};
390 LIBC_NAMESPACE::shared::ExpandedFloat<_Fp> __expanded_float = {0, 0};
391 if (__fractional.__mantissa != 0) {
392 // This function expects to parse a positive value. This means it does not
393 // take a __first, __n as arguments, since __first points to '-' for
394 // negative values.
395 auto __temp = LIBC_NAMESPACE::shared::decimal_exp_to_float<_Fp>(
396 {__fractional.__mantissa, __exponent},
397 __fractional.__truncated,
398 LIBC_NAMESPACE::shared::RoundDirection::Nearest,
399 __ptr,
400 __last - __ptr);
401 __expanded_float = __temp.num;
402 if (__temp.error == ERANGE) {
403 __result.__ec = errc::result_out_of_range;
404 }
405 }
406
407 return std::__calculate_result(__expanded_float.mantissa, __expanded_float.exponent, __negative, __result);
408}
409
410template <floating_point _Fp>
411__from_chars_result<_Fp>
412__from_chars_floating_point_impl(const char* const __first, const char* __last, chars_format __fmt) {
413 if (__first == __last) [[unlikely]]
414 return {_Fp{0}, 0, errc::invalid_argument};
415
416 const char* __ptr = __first;
417 bool __negative = *__ptr == '-';
418 if (__negative) {
419 ++__ptr;
420 if (__ptr == __last) [[unlikely]]
421 return {_Fp{0}, 0, errc::invalid_argument};
422 }
423
424 // [charconv.from.chars]
425 // [Note 1: If the pattern allows for an optional sign, but the string has
426 // no digit characters following the sign, no characters match the pattern.
427 // -- end note]
428 // This is true for integrals, floating point allows -.0
429
430 // [charconv.from.chars]/6.2
431 // if fmt has chars_format::scientific set but not chars_format::fixed, the
432 // otherwise optional exponent part shall appear;
433 // Since INF/NAN do not have an exponent this value is not valid.
434 //
435 // LWG3456 Pattern used by std::from_chars is underspecified
436 // Does not address this point, but proposed option B does solve this issue,
437 // Both MSVC STL and libstdc++ implement this this behaviour.
438 switch (std::tolower(c: *__ptr)) {
439 case 'i':
440 return std::__from_chars_floating_point_inf<_Fp>(__first, __last, __ptr + 1, __negative);
441 case 'n':
442 if constexpr (numeric_limits<_Fp>::has_quiet_NaN)
443 // NOTE: The pointer passed here will be parsed in the default C locale.
444 // This is standard behavior (see https://eel.is/c++draft/charconv.from.chars), but may be unexpected.
445 return std::__from_chars_floating_point_nan<_Fp>(__first, __last, __ptr + 1, __negative);
446 return {_Fp{0}, 0, errc::invalid_argument};
447 }
448
449 if (__fmt == chars_format::hex)
450 return std::__from_chars_floating_point_hex<_Fp>(__first, __last, __ptr, __negative);
451
452 return std::__from_chars_floating_point_decimal<_Fp>(__first, __last, __fmt, __ptr, __negative);
453}
454
455_LIBCPP_END_NAMESPACE_STD
456
457#endif //_LIBCPP_SRC_INCLUDE_FROM_CHARS_FLOATING_POINT_H
458