1//===-- String to float conversion utils ------------------------*- C++ -*-===//
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// -----------------------------------------------------------------------------
10// **** WARNING ****
11// This file is shared with libc++. You should also be careful when adding
12// dependencies to this file, since it needs to build for all libc++ targets.
13// -----------------------------------------------------------------------------
14
15#ifndef LLVM_LIBC_SRC___SUPPORT_STR_TO_FLOAT_H
16#define LLVM_LIBC_SRC___SUPPORT_STR_TO_FLOAT_H
17
18#include "hdr/errno_macros.h" // For ERANGE
19#include "src/__support/CPP/bit.h"
20#include "src/__support/CPP/limits.h"
21#include "src/__support/CPP/optional.h"
22#include "src/__support/CPP/string_view.h"
23#include "src/__support/FPUtil/FPBits.h"
24#include "src/__support/FPUtil/rounding_mode.h"
25#include "src/__support/common.h"
26#include "src/__support/ctype_utils.h"
27#include "src/__support/detailed_powers_of_ten.h"
28#include "src/__support/high_precision_decimal.h"
29#include "src/__support/macros/config.h"
30#include "src/__support/macros/null_check.h"
31#include "src/__support/macros/optimization.h"
32#include "src/__support/str_to_integer.h"
33#include "src/__support/str_to_num_result.h"
34#include "src/__support/uint128.h"
35
36#include <stdint.h>
37
38namespace LIBC_NAMESPACE_DECL {
39namespace internal {
40
41// -----------------------------------------------------------------------------
42// **** WARNING ****
43// This interface is shared with libc++, if you change this interface you need
44// to update it in both libc and libc++.
45// -----------------------------------------------------------------------------
46template <class T> struct ExpandedFloat {
47 typename fputil::FPBits<T>::StorageType mantissa;
48 int32_t exponent;
49};
50
51// -----------------------------------------------------------------------------
52// **** WARNING ****
53// This interface is shared with libc++, if you change this interface you need
54// to update it in both libc and libc++.
55// -----------------------------------------------------------------------------
56template <class T> struct FloatConvertReturn {
57 ExpandedFloat<T> num = {0, 0};
58 int error = 0;
59};
60
61LIBC_INLINE uint64_t low64(const UInt128 &num) {
62 return static_cast<uint64_t>(num & 0xffffffffffffffff);
63}
64
65LIBC_INLINE uint64_t high64(const UInt128 &num) {
66 return static_cast<uint64_t>(num >> 64);
67}
68
69template <class T> LIBC_INLINE void set_implicit_bit(fputil::FPBits<T> &) {
70 return;
71}
72
73#if defined(LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80)
74template <>
75LIBC_INLINE void
76set_implicit_bit<long double>(fputil::FPBits<long double> &result) {
77 result.set_implicit_bit(result.get_biased_exponent() != 0);
78}
79#endif // LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80
80
81// This Eisel-Lemire implementation is based on the algorithm described in the
82// paper Number Parsing at a Gigabyte per Second, Software: Practice and
83// Experience 51 (8), 2021 (https://arxiv.org/abs/2101.11408), as well as the
84// description by Nigel Tao
85// (https://nigeltao.github.io/blog/2020/eisel-lemire.html) and the golang
86// implementation, also by Nigel Tao
87// (https://github.com/golang/go/blob/release-branch.go1.16/src/strconv/eisel_lemire.go#L25)
88// for some optimizations as well as handling 32 bit floats.
89template <class T>
90LIBC_INLINE cpp::optional<ExpandedFloat<T>>
91eisel_lemire(ExpandedFloat<T> init_num,
92 RoundDirection round = RoundDirection::Nearest) {
93 using FPBits = typename fputil::FPBits<T>;
94 using StorageType = typename FPBits::StorageType;
95
96 StorageType mantissa = init_num.mantissa;
97 int32_t exp10 = init_num.exponent;
98
99 if (sizeof(T) > 8) { // This algorithm cannot handle anything longer than a
100 // double, so we skip straight to the fallback.
101 return cpp::nullopt;
102 }
103
104 // Exp10 Range
105 if (exp10 < DETAILED_POWERS_OF_TEN_MIN_EXP_10 ||
106 exp10 > DETAILED_POWERS_OF_TEN_MAX_EXP_10) {
107 return cpp::nullopt;
108 }
109
110 // Normalization
111 uint32_t clz = static_cast<uint32_t>(cpp::countl_zero<StorageType>(mantissa));
112 mantissa <<= clz;
113
114 int32_t exp2 = exp10_to_exp2(exp10) + FPBits::STORAGE_LEN + FPBits::EXP_BIAS -
115 static_cast<int32_t>(clz);
116
117 // Multiplication
118 const uint64_t *power_of_ten =
119 DETAILED_POWERS_OF_TEN[exp10 - DETAILED_POWERS_OF_TEN_MIN_EXP_10];
120
121 UInt128 first_approx =
122 static_cast<UInt128>(mantissa) * static_cast<UInt128>(power_of_ten[1]);
123
124 // Wider Approximation
125 UInt128 final_approx;
126 // The halfway constant is used to check if the bits that will be shifted away
127 // intially are all 1. For doubles this is 64 (bitstype size) - 52 (final
128 // mantissa size) - 3 (we shift away the last two bits separately for
129 // accuracy, and the most significant bit is ignored.) = 9 bits. Similarly,
130 // it's 6 bits for floats in this case.
131 const uint64_t halfway_constant =
132 (uint64_t(1) << (FPBits::STORAGE_LEN - (FPBits::FRACTION_LEN + 3))) - 1;
133 if ((high64(num: first_approx) & halfway_constant) == halfway_constant &&
134 low64(num: first_approx) + mantissa < mantissa) {
135 UInt128 low_bits =
136 static_cast<UInt128>(mantissa) * static_cast<UInt128>(power_of_ten[0]);
137 UInt128 second_approx =
138 first_approx + static_cast<UInt128>(high64(num: low_bits));
139
140 if ((high64(num: second_approx) & halfway_constant) == halfway_constant &&
141 low64(num: second_approx) + 1 == 0 &&
142 low64(num: low_bits) + mantissa < mantissa) {
143 return cpp::nullopt;
144 }
145 final_approx = second_approx;
146 } else {
147 final_approx = first_approx;
148 }
149
150 // Shifting to 54 bits for doubles and 25 bits for floats
151 StorageType msb = static_cast<StorageType>(high64(num: final_approx) >>
152 (FPBits::STORAGE_LEN - 1));
153 StorageType final_mantissa = static_cast<StorageType>(
154 high64(num: final_approx) >>
155 (msb + FPBits::STORAGE_LEN - (FPBits::FRACTION_LEN + 3)));
156 exp2 -= static_cast<uint32_t>(1 ^ msb); // same as !msb
157
158 if (round == RoundDirection::Nearest) {
159 // Half-way ambiguity
160 if (low64(num: final_approx) == 0 &&
161 (high64(num: final_approx) & halfway_constant) == 0 &&
162 (final_mantissa & 3) == 1) {
163 return cpp::nullopt;
164 }
165
166 // Round to even.
167 final_mantissa += final_mantissa & 1;
168
169 } else if (round == RoundDirection::Up) {
170 // If any of the bits being rounded away are non-zero, then round up.
171 if (low64(num: final_approx) > 0 ||
172 (high64(num: final_approx) & halfway_constant) > 0) {
173 // Add two since the last current lowest bit is about to be shifted away.
174 final_mantissa += 2;
175 }
176 }
177 // else round down, which has no effect.
178
179 // From 54 to 53 bits for doubles and 25 to 24 bits for floats
180 final_mantissa >>= 1;
181 if ((final_mantissa >> (FPBits::FRACTION_LEN + 1)) > 0) {
182 final_mantissa >>= 1;
183 ++exp2;
184 }
185
186 // The if block is equivalent to (but has fewer branches than):
187 // if exp2 <= 0 || exp2 >= 0x7FF { etc }
188 if (static_cast<uint32_t>(exp2) - 1 >= (1 << FPBits::EXP_LEN) - 2) {
189 return cpp::nullopt;
190 }
191
192 ExpandedFloat<T> output;
193 output.mantissa = final_mantissa;
194 output.exponent = exp2;
195 return output;
196}
197
198// TODO: Re-enable eisel-lemire for long double is double double once it's
199// properly supported.
200#if !defined(LIBC_TYPES_LONG_DOUBLE_IS_FLOAT64) && \
201 !defined(LIBC_TYPES_LONG_DOUBLE_IS_DOUBLE_DOUBLE)
202template <>
203LIBC_INLINE cpp::optional<ExpandedFloat<long double>>
204eisel_lemire<long double>(ExpandedFloat<long double> init_num,
205 RoundDirection round) {
206 using FPBits = typename fputil::FPBits<long double>;
207 using StorageType = typename FPBits::StorageType;
208
209 UInt128 mantissa = init_num.mantissa;
210 int32_t exp10 = init_num.exponent;
211
212 // Exp10 Range
213 // This doesn't reach very far into the range for long doubles, since it's
214 // sized for doubles and their 11 exponent bits, and not for long doubles and
215 // their 15 exponent bits (max exponent of ~300 for double vs ~5000 for long
216 // double). This is a known tradeoff, and was made because a proper long
217 // double table would be approximately 16 times larger. This would have
218 // significant memory and storage costs all the time to speed up a relatively
219 // uncommon path. In addition the exp10_to_exp2 function only approximates
220 // multiplying by log(10)/log(2), and that approximation may not be accurate
221 // out to the full long double range.
222 if (exp10 < DETAILED_POWERS_OF_TEN_MIN_EXP_10 ||
223 exp10 > DETAILED_POWERS_OF_TEN_MAX_EXP_10) {
224 return cpp::nullopt;
225 }
226
227 // Normalization
228 int32_t clz = static_cast<int32_t>(cpp::countl_zero(value: mantissa)) -
229 ((sizeof(UInt128) - sizeof(StorageType)) * CHAR_BIT);
230 mantissa <<= clz;
231
232 int32_t exp2 =
233 exp10_to_exp2(exp10) + FPBits::STORAGE_LEN + FPBits::EXP_BIAS - clz;
234
235 // Multiplication
236 const uint64_t *power_of_ten =
237 DETAILED_POWERS_OF_TEN[exp10 - DETAILED_POWERS_OF_TEN_MIN_EXP_10];
238
239 // Since the input mantissa is more than 64 bits, we have to multiply with the
240 // full 128 bits of the power of ten to get an approximation with the same
241 // number of significant bits. This means that we only get the one
242 // approximation, and that approximation is 256 bits long.
243 UInt128 approx_upper = static_cast<UInt128>(high64(num: mantissa)) *
244 static_cast<UInt128>(power_of_ten[1]);
245
246 UInt128 approx_middle_a = static_cast<UInt128>(high64(num: mantissa)) *
247 static_cast<UInt128>(power_of_ten[0]);
248 UInt128 approx_middle_b = static_cast<UInt128>(low64(num: mantissa)) *
249 static_cast<UInt128>(power_of_ten[1]);
250
251 UInt128 approx_middle = approx_middle_a + approx_middle_b;
252
253 // Handle overflow in the middle
254 approx_upper += (approx_middle < approx_middle_a) ? UInt128(1) << 64 : 0;
255
256 UInt128 approx_lower = static_cast<UInt128>(low64(num: mantissa)) *
257 static_cast<UInt128>(power_of_ten[0]);
258
259 UInt128 final_approx_lower =
260 approx_lower + (static_cast<UInt128>(low64(num: approx_middle)) << 64);
261 UInt128 final_approx_upper = approx_upper + high64(num: approx_middle) +
262 (final_approx_lower < approx_lower ? 1 : 0);
263
264 // The halfway constant is used to check if the bits that will be shifted away
265 // intially are all 1. For 80 bit floats this is 128 (bitstype size) - 64
266 // (final mantissa size) - 3 (we shift away the last two bits separately for
267 // accuracy, and the most significant bit is ignored.) = 61 bits. Similarly,
268 // it's 12 bits for 128 bit floats in this case.
269 constexpr UInt128 HALFWAY_CONSTANT =
270 (UInt128(1) << (FPBits::STORAGE_LEN - (FPBits::FRACTION_LEN + 3))) - 1;
271
272 if ((final_approx_upper & HALFWAY_CONSTANT) == HALFWAY_CONSTANT &&
273 final_approx_lower + mantissa < mantissa) {
274 return cpp::nullopt;
275 }
276
277 // Shifting to 65 bits for 80 bit floats and 113 bits for 128 bit floats
278 uint32_t msb =
279 static_cast<uint32_t>(final_approx_upper >> (FPBits::STORAGE_LEN - 1));
280 UInt128 final_mantissa = final_approx_upper >> (msb + FPBits::STORAGE_LEN -
281 (FPBits::FRACTION_LEN + 3));
282 exp2 -= static_cast<uint32_t>(1 ^ msb); // same as !msb
283
284 if (round == RoundDirection::Nearest) {
285 // Half-way ambiguity
286 if (final_approx_lower == 0 &&
287 (final_approx_upper & HALFWAY_CONSTANT) == 0 &&
288 (final_mantissa & 3) == 1) {
289 return cpp::nullopt;
290 }
291 // Round to even.
292 final_mantissa += final_mantissa & 1;
293
294 } else if (round == RoundDirection::Up) {
295 // If any of the bits being rounded away are non-zero, then round up.
296 if (final_approx_lower > 0 || (final_approx_upper & HALFWAY_CONSTANT) > 0) {
297 // Add two since the last current lowest bit is about to be shifted away.
298 final_mantissa += 2;
299 }
300 }
301 // else round down, which has no effect.
302
303 // From 65 to 64 bits for 80 bit floats and 113 to 112 bits for 128 bit
304 // floats
305 final_mantissa >>= 1;
306 if ((final_mantissa >> (FPBits::FRACTION_LEN + 1)) > 0) {
307 final_mantissa >>= 1;
308 ++exp2;
309 }
310
311 // The if block is equivalent to (but has fewer branches than):
312 // if exp2 <= 0 || exp2 >= MANTISSA_MAX { etc }
313 if (exp2 - 1 >= (1 << FPBits::EXP_LEN) - 2) {
314 return cpp::nullopt;
315 }
316
317 ExpandedFloat<long double> output;
318 output.mantissa = static_cast<StorageType>(final_mantissa);
319 output.exponent = exp2;
320 return output;
321}
322#endif // !defined(LIBC_TYPES_LONG_DOUBLE_IS_FLOAT64) &&
323 // !defined(LIBC_TYPES_LONG_DOUBLE_IS_DOUBLE_DOUBLE)
324
325// The nth item in POWERS_OF_TWO represents the greatest power of two less than
326// 10^n. This tells us how much we can safely shift without overshooting.
327constexpr uint8_t POWERS_OF_TWO[19] = {
328 0, 3, 6, 9, 13, 16, 19, 23, 26, 29, 33, 36, 39, 43, 46, 49, 53, 56, 59,
329};
330constexpr int32_t NUM_POWERS_OF_TWO =
331 sizeof(POWERS_OF_TWO) / sizeof(POWERS_OF_TWO[0]);
332
333// Takes a mantissa and base 10 exponent and converts it into its closest
334// floating point type T equivalent. This is the fallback algorithm used when
335// the Eisel-Lemire algorithm fails, it's slower but more accurate. It's based
336// on the Simple Decimal Conversion algorithm by Nigel Tao, described at this
337// link: https://nigeltao.github.io/blog/2020/parse-number-f64-simple.html
338template <class T>
339LIBC_INLINE FloatConvertReturn<T> simple_decimal_conversion(
340 const char *__restrict numStart,
341 const size_t num_len = cpp::numeric_limits<size_t>::max(),
342 RoundDirection round = RoundDirection::Nearest) {
343 using FPBits = typename fputil::FPBits<T>;
344 using StorageType = typename FPBits::StorageType;
345
346 int32_t exp2 = 0;
347 HighPrecisionDecimal hpd = HighPrecisionDecimal(numStart, num_len);
348
349 FloatConvertReturn<T> output;
350
351 if (hpd.get_num_digits() == 0) {
352 output.num = {0, 0};
353 return output;
354 }
355
356 // If the exponent is too large and can't be represented in this size of
357 // float, return inf.
358 if (hpd.get_decimal_point() > 0 &&
359 exp10_to_exp2(exp10: hpd.get_decimal_point() - 1) > FPBits::EXP_BIAS) {
360 output.num = {0, fputil::FPBits<T>::MAX_BIASED_EXPONENT};
361 output.error = ERANGE;
362 return output;
363 }
364 // If the exponent is too small even for a subnormal, return 0.
365 if (hpd.get_decimal_point() < 0 &&
366 exp10_to_exp2(exp10: -hpd.get_decimal_point()) >
367 (FPBits::EXP_BIAS + static_cast<int32_t>(FPBits::FRACTION_LEN))) {
368 output.num = {0, 0};
369 output.error = ERANGE;
370 return output;
371 }
372
373 // Right shift until the number is smaller than 1.
374 while (hpd.get_decimal_point() > 0) {
375 int32_t shift_amount = 0;
376 if (hpd.get_decimal_point() >= NUM_POWERS_OF_TWO) {
377 shift_amount = 60;
378 } else {
379 shift_amount = POWERS_OF_TWO[hpd.get_decimal_point()];
380 }
381 exp2 += shift_amount;
382 hpd.shift(shift_amount: -shift_amount);
383 }
384
385 // Left shift until the number is between 1/2 and 1
386 while (hpd.get_decimal_point() < 0 ||
387 (hpd.get_decimal_point() == 0 && hpd.get_digits()[0] < 5)) {
388 int32_t shift_amount = 0;
389
390 if (-hpd.get_decimal_point() >= NUM_POWERS_OF_TWO) {
391 shift_amount = 60;
392 } else if (hpd.get_decimal_point() != 0) {
393 shift_amount = POWERS_OF_TWO[-hpd.get_decimal_point()];
394 } else { // This handles the case of the number being between .1 and .5
395 shift_amount = 1;
396 }
397 exp2 -= shift_amount;
398 hpd.shift(shift_amount);
399 }
400
401 // Left shift once so that the number is between 1 and 2
402 --exp2;
403 hpd.shift(shift_amount: 1);
404
405 // Get the biased exponent
406 exp2 += FPBits::EXP_BIAS;
407
408 // Handle the exponent being too large (and return inf).
409 if (exp2 >= FPBits::MAX_BIASED_EXPONENT) {
410 output.num = {0, FPBits::MAX_BIASED_EXPONENT};
411 output.error = ERANGE;
412 return output;
413 }
414
415 // Shift left to fill the mantissa
416 hpd.shift(shift_amount: FPBits::FRACTION_LEN);
417 StorageType final_mantissa = hpd.round_to_integer_type<StorageType>();
418
419 // Handle subnormals
420 if (exp2 <= 0) {
421 // Shift right until there is a valid exponent
422 while (exp2 < 0) {
423 hpd.shift(shift_amount: -1);
424 ++exp2;
425 }
426 // Shift right one more time to compensate for the left shift to get it
427 // between 1 and 2.
428 hpd.shift(shift_amount: -1);
429 final_mantissa = hpd.round_to_integer_type<StorageType>(round);
430
431 // Check if by shifting right we've caused this to round to a normal number.
432 if ((final_mantissa >> FPBits::FRACTION_LEN) != 0) {
433 ++exp2;
434 }
435 }
436
437 // Check if rounding added a bit, and shift down if that's the case.
438 if (final_mantissa == StorageType(2) << FPBits::FRACTION_LEN) {
439 final_mantissa >>= 1;
440 ++exp2;
441
442 // Check if this rounding causes exp2 to go out of range and make the result
443 // INF. If this is the case, then finalMantissa and exp2 are already the
444 // correct values for an INF result.
445 if (exp2 >= FPBits::MAX_BIASED_EXPONENT) {
446 output.error = ERANGE;
447 }
448 }
449
450 if (exp2 == 0) {
451 output.error = ERANGE;
452 }
453
454 output.num = {final_mantissa, exp2};
455 return output;
456}
457
458// This class is used for templating the constants for Clinger's Fast Path,
459// described as a method of approximation in
460// Clinger WD. How to Read Floating Point Numbers Accurately. SIGPLAN Not 1990
461// Jun;25(6):92–101. https://doi.org/10.1145/93548.93557.
462// As well as the additions by Gay that extend the useful range by the number of
463// exact digits stored by the float type, described in
464// Gay DM, Correctly rounded binary-decimal and decimal-binary conversions;
465// 1990. AT&T Bell Laboratories Numerical Analysis Manuscript 90-10.
466template <class T> class ClingerConsts;
467
468template <> class ClingerConsts<float> {
469public:
470 static constexpr float POWERS_OF_TEN_ARRAY[] = {1e0, 1e1, 1e2, 1e3, 1e4, 1e5,
471 1e6, 1e7, 1e8, 1e9, 1e10};
472 static constexpr int32_t EXACT_POWERS_OF_TEN = 10;
473 static constexpr int32_t DIGITS_IN_MANTISSA = 7;
474 static constexpr float MAX_EXACT_INT = 16777215.0;
475};
476
477template <> class ClingerConsts<double> {
478public:
479 static constexpr double POWERS_OF_TEN_ARRAY[] = {
480 1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11,
481 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22};
482 static constexpr int32_t EXACT_POWERS_OF_TEN = 22;
483 static constexpr int32_t DIGITS_IN_MANTISSA = 15;
484 static constexpr double MAX_EXACT_INT = 9007199254740991.0;
485};
486
487#if defined(LIBC_TYPES_LONG_DOUBLE_IS_FLOAT64)
488template <> class ClingerConsts<long double> {
489public:
490 static constexpr long double POWERS_OF_TEN_ARRAY[] = {
491 1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11,
492 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22};
493 static constexpr int32_t EXACT_POWERS_OF_TEN =
494 ClingerConsts<double>::EXACT_POWERS_OF_TEN;
495 static constexpr int32_t DIGITS_IN_MANTISSA =
496 ClingerConsts<double>::DIGITS_IN_MANTISSA;
497 static constexpr long double MAX_EXACT_INT =
498 ClingerConsts<double>::MAX_EXACT_INT;
499};
500#elif defined(LIBC_TYPES_LONG_DOUBLE_IS_X86_FLOAT80)
501template <> class ClingerConsts<long double> {
502public:
503 static constexpr long double POWERS_OF_TEN_ARRAY[] = {
504 1e0L, 1e1L, 1e2L, 1e3L, 1e4L, 1e5L, 1e6L, 1e7L, 1e8L, 1e9L,
505 1e10L, 1e11L, 1e12L, 1e13L, 1e14L, 1e15L, 1e16L, 1e17L, 1e18L, 1e19L,
506 1e20L, 1e21L, 1e22L, 1e23L, 1e24L, 1e25L, 1e26L, 1e27L};
507 static constexpr int32_t EXACT_POWERS_OF_TEN = 27;
508 static constexpr int32_t DIGITS_IN_MANTISSA = 21;
509 static constexpr long double MAX_EXACT_INT = 18446744073709551615.0L;
510};
511#elif defined(LIBC_TYPES_LONG_DOUBLE_IS_FLOAT128)
512template <> class ClingerConsts<long double> {
513public:
514 static constexpr long double POWERS_OF_TEN_ARRAY[] = {
515 1e0L, 1e1L, 1e2L, 1e3L, 1e4L, 1e5L, 1e6L, 1e7L, 1e8L, 1e9L,
516 1e10L, 1e11L, 1e12L, 1e13L, 1e14L, 1e15L, 1e16L, 1e17L, 1e18L, 1e19L,
517 1e20L, 1e21L, 1e22L, 1e23L, 1e24L, 1e25L, 1e26L, 1e27L, 1e28L, 1e29L,
518 1e30L, 1e31L, 1e32L, 1e33L, 1e34L, 1e35L, 1e36L, 1e37L, 1e38L, 1e39L,
519 1e40L, 1e41L, 1e42L, 1e43L, 1e44L, 1e45L, 1e46L, 1e47L, 1e48L};
520 static constexpr int32_t EXACT_POWERS_OF_TEN = 48;
521 static constexpr int32_t DIGITS_IN_MANTISSA = 33;
522 static constexpr long double MAX_EXACT_INT =
523 10384593717069655257060992658440191.0L;
524};
525#elif defined(LIBC_TYPES_LONG_DOUBLE_IS_DOUBLE_DOUBLE)
526// TODO: Add proper double double type support here, currently using constants
527// for double since it should be safe.
528template <> class ClingerConsts<long double> {
529public:
530 static constexpr double POWERS_OF_TEN_ARRAY[] = {
531 1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11,
532 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22};
533 static constexpr int32_t EXACT_POWERS_OF_TEN = 22;
534 static constexpr int32_t DIGITS_IN_MANTISSA = 15;
535 static constexpr double MAX_EXACT_INT = 9007199254740991.0;
536};
537#else
538#error "Unknown long double type"
539#endif
540
541// Take an exact mantissa and exponent and attempt to convert it using only
542// exact floating point arithmetic. This only handles numbers with low
543// exponents, but handles them quickly. This is an implementation of Clinger's
544// Fast Path, as described above.
545template <class T>
546LIBC_INLINE cpp::optional<ExpandedFloat<T>>
547clinger_fast_path(ExpandedFloat<T> init_num,
548 RoundDirection round = RoundDirection::Nearest) {
549 using FPBits = typename fputil::FPBits<T>;
550 using StorageType = typename FPBits::StorageType;
551
552 StorageType mantissa = init_num.mantissa;
553 int32_t exp10 = init_num.exponent;
554
555 if ((mantissa >> FPBits::FRACTION_LEN) > 0) {
556 return cpp::nullopt;
557 }
558
559 FPBits result;
560 T float_mantissa;
561 if constexpr (is_big_int_v<StorageType> || sizeof(T) > sizeof(uint64_t)) {
562 float_mantissa =
563 (static_cast<T>(uint64_t(mantissa >> 64)) * static_cast<T>(0x1.0p64)) +
564 static_cast<T>(uint64_t(mantissa));
565 } else {
566 float_mantissa = static_cast<T>(mantissa);
567 }
568
569 if (exp10 == 0) {
570 result = FPBits(float_mantissa);
571 }
572 if (exp10 > 0) {
573 if (exp10 > ClingerConsts<T>::EXACT_POWERS_OF_TEN +
574 ClingerConsts<T>::DIGITS_IN_MANTISSA) {
575 return cpp::nullopt;
576 }
577 if (exp10 > ClingerConsts<T>::EXACT_POWERS_OF_TEN) {
578 float_mantissa = float_mantissa *
579 ClingerConsts<T>::POWERS_OF_TEN_ARRAY
580 [exp10 - ClingerConsts<T>::EXACT_POWERS_OF_TEN];
581 exp10 = ClingerConsts<T>::EXACT_POWERS_OF_TEN;
582 }
583 if (float_mantissa > ClingerConsts<T>::MAX_EXACT_INT) {
584 return cpp::nullopt;
585 }
586 result =
587 FPBits(float_mantissa * ClingerConsts<T>::POWERS_OF_TEN_ARRAY[exp10]);
588 } else if (exp10 < 0) {
589 if (-exp10 > ClingerConsts<T>::EXACT_POWERS_OF_TEN) {
590 return cpp::nullopt;
591 }
592 result =
593 FPBits(float_mantissa / ClingerConsts<T>::POWERS_OF_TEN_ARRAY[-exp10]);
594 }
595
596 // If the rounding mode is not nearest, then the sign of the number may affect
597 // the result. To make sure the rounding mode is respected properly, the
598 // calculation is redone with a negative result, and the rounding mode is used
599 // to select the correct result.
600 if (round != RoundDirection::Nearest) {
601 FPBits negative_result;
602 // I'm 99% sure this will break under fast math optimizations.
603 negative_result = FPBits((-float_mantissa) *
604 ClingerConsts<T>::POWERS_OF_TEN_ARRAY[exp10]);
605
606 // If the results are equal, then we don't need to use the rounding mode.
607 if (result.get_val() != -negative_result.get_val()) {
608 FPBits lower_result;
609 FPBits higher_result;
610
611 if (result.get_val() < -negative_result.get_val()) {
612 lower_result = result;
613 higher_result = negative_result;
614 } else {
615 lower_result = negative_result;
616 higher_result = result;
617 }
618
619 if (round == RoundDirection::Up) {
620 result = higher_result;
621 } else {
622 result = lower_result;
623 }
624 }
625 }
626
627 ExpandedFloat<T> output;
628 output.mantissa = result.get_explicit_mantissa();
629 output.exponent = result.get_biased_exponent();
630 return output;
631}
632
633// The upper bound is the highest base-10 exponent that could possibly give a
634// non-inf result for this size of float. The value is
635// log10(2^(exponent bias)).
636// The generic approximation uses the fact that log10(2^x) ~= x/3
637template <typename T> LIBC_INLINE constexpr int32_t get_upper_bound() {
638 return fputil::FPBits<T>::EXP_BIAS / 3;
639}
640
641template <> LIBC_INLINE constexpr int32_t get_upper_bound<float>() {
642 return 39;
643}
644
645template <> LIBC_INLINE constexpr int32_t get_upper_bound<double>() {
646 return 309;
647}
648
649// The lower bound is the largest negative base-10 exponent that could possibly
650// give a non-zero result for this size of float. The value is
651// log10(2^(exponent bias + final mantissa width + intermediate mantissa width))
652// The intermediate mantissa is the integer that's been parsed from the string,
653// and the final mantissa is the fractional part of the output number. A very
654// low base 10 exponent with a very high intermediate mantissa can cancel each
655// other out, and subnormal numbers allow for the result to be at the very low
656// end of the final mantissa.
657template <typename T> LIBC_INLINE constexpr int32_t get_lower_bound() {
658 using FPBits = typename fputil::FPBits<T>;
659 return -((FPBits::EXP_BIAS +
660 static_cast<int32_t>(FPBits::FRACTION_LEN + FPBits::STORAGE_LEN)) /
661 3);
662}
663
664template <> LIBC_INLINE constexpr int32_t get_lower_bound<float>() {
665 return -(39 + 6 + 10);
666}
667
668template <> LIBC_INLINE constexpr int32_t get_lower_bound<double>() {
669 return -(309 + 15 + 20);
670}
671
672// -----------------------------------------------------------------------------
673// **** WARNING ****
674// This interface is shared with libc++, if you change this interface you need
675// to update it in both libc and libc++.
676// -----------------------------------------------------------------------------
677// Takes a mantissa and base 10 exponent and converts it into its closest
678// floating point type T equivalient. First we try the Eisel-Lemire algorithm,
679// then if that fails then we fall back to a more accurate algorithm for
680// accuracy. The resulting mantissa and exponent are placed in outputMantissa
681// and outputExp2.
682template <class T>
683LIBC_INLINE FloatConvertReturn<T> decimal_exp_to_float(
684 ExpandedFloat<T> init_num, bool truncated, RoundDirection round,
685 const char *__restrict numStart,
686 const size_t num_len = cpp::numeric_limits<size_t>::max()) {
687 using FPBits = typename fputil::FPBits<T>;
688 using StorageType = typename FPBits::StorageType;
689
690 StorageType mantissa = init_num.mantissa;
691 int32_t exp10 = init_num.exponent;
692
693 FloatConvertReturn<T> output;
694 cpp::optional<ExpandedFloat<T>> opt_output;
695
696 // If the exponent is too large and can't be represented in this size of
697 // float, return inf. These bounds are relatively loose, but are mostly
698 // serving as a first pass. Some close numbers getting through is okay.
699 if (exp10 > get_upper_bound<T>()) {
700 output.num = {0, FPBits::MAX_BIASED_EXPONENT};
701 output.error = ERANGE;
702 return output;
703 }
704 // If the exponent is too small even for a subnormal, return 0.
705 if (exp10 < get_lower_bound<T>()) {
706 output.num = {0, 0};
707 output.error = ERANGE;
708 return output;
709 }
710
711 // Clinger's Fast Path and Eisel-Lemire can't set errno, but they can fail.
712 // For this reason the "error" field in their return values is used to
713 // represent whether they've failed as opposed to the errno value. Any
714 // non-zero value represents a failure.
715
716#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH
717 if (!truncated) {
718 opt_output = clinger_fast_path<T>(init_num, round);
719 // If the algorithm succeeded the error will be 0, else it will be a
720 // non-zero number.
721 if (opt_output.has_value()) {
722 return {opt_output.value(), 0};
723 }
724 }
725#endif // LIBC_COPT_STRTOFLOAT_DISABLE_CLINGER_FAST_PATH
726
727#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE
728 // Try Eisel-Lemire
729 opt_output = eisel_lemire<T>(init_num, round);
730 if (opt_output.has_value()) {
731 if (!truncated) {
732 return {opt_output.value(), 0};
733 }
734 // If the mantissa is truncated, then the result may be off by the LSB, so
735 // check if rounding the mantissa up changes the result. If not, then it's
736 // safe, else use the fallback.
737 auto second_output = eisel_lemire<T>({mantissa + 1, exp10}, round);
738 if (second_output.has_value()) {
739 if (opt_output->mantissa == second_output->mantissa &&
740 opt_output->exponent == second_output->exponent) {
741 return {opt_output.value(), 0};
742 }
743 }
744 }
745#endif // LIBC_COPT_STRTOFLOAT_DISABLE_EISEL_LEMIRE
746
747#ifndef LIBC_COPT_STRTOFLOAT_DISABLE_SIMPLE_DECIMAL_CONVERSION
748 output = simple_decimal_conversion<T>(numStart, num_len, round);
749#else
750#warning "Simple decimal conversion is disabled, result may not be correct."
751#endif // LIBC_COPT_STRTOFLOAT_DISABLE_SIMPLE_DECIMAL_CONVERSION
752
753 return output;
754}
755
756// -----------------------------------------------------------------------------
757// **** WARNING ****
758// This interface is shared with libc++, if you change this interface you need
759// to update it in both libc and libc++.
760// -----------------------------------------------------------------------------
761// Takes a mantissa and base 2 exponent and converts it into its closest
762// floating point type T equivalient. Since the exponent is already in the right
763// form, this is mostly just shifting and rounding. This is used for hexadecimal
764// numbers since a base 16 exponent multiplied by 4 is the base 2 exponent.
765template <class T>
766LIBC_INLINE FloatConvertReturn<T> binary_exp_to_float(ExpandedFloat<T> init_num,
767 bool truncated,
768 RoundDirection round) {
769 using FPBits = typename fputil::FPBits<T>;
770 using StorageType = typename FPBits::StorageType;
771
772 StorageType mantissa = init_num.mantissa;
773 int32_t exp2 = init_num.exponent;
774
775 FloatConvertReturn<T> output;
776
777 // This is the number of leading zeroes a properly normalized float of type T
778 // should have.
779 constexpr int32_t INF_EXP = (1 << FPBits::EXP_LEN) - 1;
780
781 // Normalization step 1: Bring the leading bit to the highest bit of
782 // StorageType.
783 uint32_t amount_to_shift_left = cpp::countl_zero<StorageType>(mantissa);
784 mantissa <<= amount_to_shift_left;
785
786 // Keep exp2 representing the exponent of the lowest bit of StorageType.
787 exp2 -= amount_to_shift_left;
788
789 // biased_exponent represents the biased exponent of the most significant bit.
790 int32_t biased_exponent = exp2 + FPBits::STORAGE_LEN + FPBits::EXP_BIAS - 1;
791
792 // Handle numbers that're too large and get squashed to inf
793 if (biased_exponent >= INF_EXP) {
794 // This indicates an overflow, so we make the result INF and set errno.
795 output.num = {0, (1 << FPBits::EXP_LEN) - 1};
796 output.error = ERANGE;
797 return output;
798 }
799
800 uint32_t amount_to_shift_right =
801 FPBits::STORAGE_LEN - FPBits::FRACTION_LEN - 1;
802
803 // Handle subnormals.
804 if (biased_exponent <= 0) {
805 amount_to_shift_right += static_cast<uint32_t>(1 - biased_exponent);
806 biased_exponent = 0;
807
808 if (amount_to_shift_right > FPBits::STORAGE_LEN) {
809 // Return 0 if the exponent is too small.
810 output.num = {0, 0};
811 output.error = ERANGE;
812 return output;
813 }
814 }
815
816 StorageType round_bit_mask = StorageType(1) << (amount_to_shift_right - 1);
817 StorageType sticky_mask = round_bit_mask - 1;
818 bool round_bit = static_cast<bool>(mantissa & round_bit_mask);
819 bool sticky_bit = static_cast<bool>(mantissa & sticky_mask) || truncated;
820
821 if (amount_to_shift_right < FPBits::STORAGE_LEN) {
822 // Shift the mantissa and clear the implicit bit.
823 mantissa >>= amount_to_shift_right;
824 mantissa &= FPBits::FRACTION_MASK;
825 } else {
826 mantissa = 0;
827 }
828 bool least_significant_bit = static_cast<bool>(mantissa & StorageType(1));
829
830 // TODO: check that this rounding behavior is correct.
831
832 if (round == RoundDirection::Nearest) {
833 // Perform rounding-to-nearest, tie-to-even.
834 if (round_bit && (least_significant_bit || sticky_bit)) {
835 ++mantissa;
836 }
837 } else if (round == RoundDirection::Up) {
838 if (round_bit || sticky_bit) {
839 ++mantissa;
840 }
841 } else /* (round == RoundDirection::Down)*/ {
842 if (round_bit && sticky_bit) {
843 ++mantissa;
844 }
845 }
846
847 if (mantissa > FPBits::FRACTION_MASK) {
848 // Rounding causes the exponent to increase.
849 ++biased_exponent;
850
851 if (biased_exponent == INF_EXP) {
852 output.error = ERANGE;
853 }
854 }
855
856 if (biased_exponent == 0) {
857 output.error = ERANGE;
858 }
859
860 output.num = {mantissa & FPBits::FRACTION_MASK, biased_exponent};
861 return output;
862}
863
864// checks if the next 4 characters of the string pointer are the start of a
865// hexadecimal floating point number. Does not advance the string pointer.
866LIBC_INLINE bool is_float_hex_start(const char *__restrict src,
867 const char decimalPoint) {
868 if (!(src[0] == '0' && tolower(ch: src[1]) == 'x')) {
869 return false;
870 }
871 size_t first_digit = 2;
872 if (src[2] == decimalPoint) {
873 ++first_digit;
874 }
875 return isalnum(ch: src[first_digit]) && b36_char_to_int(ch: src[first_digit]) < 16;
876}
877
878// Takes the start of a string representing a decimal float, as well as the
879// local decimalPoint. It returns if it suceeded in parsing any digits, and if
880// the return value is true then the outputs are pointer to the end of the
881// number, and the mantissa and exponent for the closest float T representation.
882// If the return value is false, then it is assumed that there is no number
883// here.
884template <class T>
885LIBC_INLINE StrToNumResult<ExpandedFloat<T>>
886decimal_string_to_float(const char *__restrict src, const char DECIMAL_POINT,
887 RoundDirection round) {
888 using FPBits = typename fputil::FPBits<T>;
889 using StorageType = typename FPBits::StorageType;
890
891 constexpr uint32_t BASE = 10;
892 constexpr char EXPONENT_MARKER = 'e';
893
894 bool truncated = false;
895 bool seen_digit = false;
896 bool after_decimal = false;
897 StorageType mantissa = 0;
898 int32_t exponent = 0;
899
900 size_t index = 0;
901
902 StrToNumResult<ExpandedFloat<T>> output({0, 0});
903
904 // The goal for the first step of parsing is to convert the number in src to
905 // the format mantissa * (base ^ exponent)
906
907 // The loop fills the mantissa with as many digits as it can hold
908 const StorageType bitstype_max_div_by_base =
909 cpp::numeric_limits<StorageType>::max() / BASE;
910 while (true) {
911 if (isdigit(ch: src[index])) {
912 uint32_t digit = static_cast<uint32_t>(b36_char_to_int(ch: src[index]));
913 seen_digit = true;
914
915 if (mantissa < bitstype_max_div_by_base) {
916 mantissa = (mantissa * BASE) + digit;
917 if (after_decimal) {
918 --exponent;
919 }
920 } else {
921 if (digit > 0)
922 truncated = true;
923 if (!after_decimal)
924 ++exponent;
925 }
926
927 ++index;
928 continue;
929 }
930 if (src[index] == DECIMAL_POINT) {
931 if (after_decimal) {
932 break; // this means that src[index] points to a second decimal point,
933 // ending the number.
934 }
935 after_decimal = true;
936 ++index;
937 continue;
938 }
939 // The character is neither a digit nor a decimal point.
940 break;
941 }
942
943 if (!seen_digit)
944 return output;
945
946 // TODO: When adding max length argument, handle the case of a trailing
947 // EXPONENT MARKER, see scanf for more details.
948 if (tolower(ch: src[index]) == EXPONENT_MARKER) {
949 bool has_sign = false;
950 if (src[index + 1] == '+' || src[index + 1] == '-') {
951 has_sign = true;
952 }
953 if (isdigit(ch: src[index + 1 + static_cast<size_t>(has_sign)])) {
954 ++index;
955 auto result = strtointeger<int32_t>(src: src + index, base: 10);
956 if (result.has_error())
957 output.error = result.error;
958 int32_t add_to_exponent = result.value;
959 index += static_cast<size_t>(result.parsed_len);
960
961 // Here we do this operation as int64 to avoid overflow.
962 int64_t temp_exponent = static_cast<int64_t>(exponent) +
963 static_cast<int64_t>(add_to_exponent);
964
965 // If the result is in the valid range, then we use it. The valid range is
966 // also within the int32 range, so this prevents overflow issues.
967 if (temp_exponent > FPBits::MAX_BIASED_EXPONENT) {
968 exponent = FPBits::MAX_BIASED_EXPONENT;
969 } else if (temp_exponent < -FPBits::MAX_BIASED_EXPONENT) {
970 exponent = -FPBits::MAX_BIASED_EXPONENT;
971 } else {
972 exponent = static_cast<int32_t>(temp_exponent);
973 }
974 }
975 }
976
977 output.parsed_len = index;
978 if (mantissa == 0) { // if we have a 0, then also 0 the exponent.
979 output.value = {0, 0};
980 } else {
981 auto temp =
982 decimal_exp_to_float<T>({mantissa, exponent}, truncated, round, src);
983 output.value = temp.num;
984 output.error = temp.error;
985 }
986 return output;
987}
988
989// Takes the start of a string representing a hexadecimal float, as well as the
990// local decimal point. It returns if it suceeded in parsing any digits, and if
991// the return value is true then the outputs are pointer to the end of the
992// number, and the mantissa and exponent for the closest float T representation.
993// If the return value is false, then it is assumed that there is no number
994// here.
995template <class T>
996LIBC_INLINE StrToNumResult<ExpandedFloat<T>>
997hexadecimal_string_to_float(const char *__restrict src,
998 const char DECIMAL_POINT, RoundDirection round) {
999 using FPBits = typename fputil::FPBits<T>;
1000 using StorageType = typename FPBits::StorageType;
1001
1002 constexpr uint32_t BASE = 16;
1003 constexpr char EXPONENT_MARKER = 'p';
1004
1005 bool truncated = false;
1006 bool seen_digit = false;
1007 bool after_decimal = false;
1008 StorageType mantissa = 0;
1009 int32_t exponent = 0;
1010
1011 size_t index = 0;
1012
1013 StrToNumResult<ExpandedFloat<T>> output({0, 0});
1014
1015 // The goal for the first step of parsing is to convert the number in src to
1016 // the format mantissa * (base ^ exponent)
1017
1018 // The loop fills the mantissa with as many digits as it can hold
1019 const StorageType bitstype_max_div_by_base =
1020 cpp::numeric_limits<StorageType>::max() / BASE;
1021 while (true) {
1022 if (isalnum(ch: src[index])) {
1023 uint32_t digit = static_cast<uint32_t>(b36_char_to_int(ch: src[index]));
1024 if (digit < BASE)
1025 seen_digit = true;
1026 else
1027 break;
1028
1029 if (mantissa < bitstype_max_div_by_base) {
1030 mantissa = (mantissa * BASE) + digit;
1031 if (after_decimal)
1032 --exponent;
1033 } else {
1034 if (digit > 0)
1035 truncated = true;
1036 if (!after_decimal)
1037 ++exponent;
1038 }
1039 ++index;
1040 continue;
1041 }
1042 if (src[index] == DECIMAL_POINT) {
1043 if (after_decimal) {
1044 break; // this means that src[index] points to a second decimal point,
1045 // ending the number.
1046 }
1047 after_decimal = true;
1048 ++index;
1049 continue;
1050 }
1051 // The character is neither a hexadecimal digit nor a decimal point.
1052 break;
1053 }
1054
1055 if (!seen_digit)
1056 return output;
1057
1058 // Convert the exponent from having a base of 16 to having a base of 2.
1059 exponent *= 4;
1060
1061 if (tolower(ch: src[index]) == EXPONENT_MARKER) {
1062 bool has_sign = false;
1063 if (src[index + 1] == '+' || src[index + 1] == '-') {
1064 has_sign = true;
1065 }
1066 if (isdigit(ch: src[index + 1 + static_cast<size_t>(has_sign)])) {
1067 ++index;
1068 auto result = strtointeger<int32_t>(src: src + index, base: 10);
1069 if (result.has_error())
1070 output.error = result.error;
1071
1072 int32_t add_to_exponent = result.value;
1073 index += static_cast<size_t>(result.parsed_len);
1074
1075 // Here we do this operation as int64 to avoid overflow.
1076 int64_t temp_exponent = static_cast<int64_t>(exponent) +
1077 static_cast<int64_t>(add_to_exponent);
1078
1079 // If the result is in the valid range, then we use it. The valid range is
1080 // also within the int32 range, so this prevents overflow issues.
1081 if (temp_exponent > FPBits::MAX_BIASED_EXPONENT) {
1082 exponent = FPBits::MAX_BIASED_EXPONENT;
1083 } else if (temp_exponent < -FPBits::MAX_BIASED_EXPONENT) {
1084 exponent = -FPBits::MAX_BIASED_EXPONENT;
1085 } else {
1086 exponent = static_cast<int32_t>(temp_exponent);
1087 }
1088 }
1089 }
1090 output.parsed_len = index;
1091 if (mantissa == 0) { // if we have a 0, then also 0 the exponent.
1092 output.value.exponent = 0;
1093 output.value.mantissa = 0;
1094 } else {
1095 auto temp = binary_exp_to_float<T>({mantissa, exponent}, truncated, round);
1096 output.error = temp.error;
1097 output.value = temp.num;
1098 }
1099 return output;
1100}
1101
1102template <class T>
1103LIBC_INLINE typename fputil::FPBits<T>::StorageType
1104nan_mantissa_from_ncharseq(const cpp::string_view ncharseq) {
1105 using FPBits = typename fputil::FPBits<T>;
1106 using StorageType = typename FPBits::StorageType;
1107
1108 StorageType nan_mantissa = 0;
1109
1110 if (ncharseq.data() != nullptr && isdigit(ch: ncharseq[0])) {
1111 StrToNumResult<StorageType> strtoint_result =
1112 strtointeger<StorageType>(ncharseq.data(), 0);
1113 if (!strtoint_result.has_error())
1114 nan_mantissa = strtoint_result.value;
1115
1116 if (strtoint_result.parsed_len != static_cast<ptrdiff_t>(ncharseq.size()))
1117 nan_mantissa = 0;
1118 }
1119
1120 return nan_mantissa;
1121}
1122
1123// Takes a pointer to a string and a pointer to a string pointer. This function
1124// is used as the backend for all of the string to float functions.
1125// TODO: Add src_len member to match strtointeger.
1126// TODO: Next, move from char* and length to string_view
1127template <class T>
1128LIBC_INLINE StrToNumResult<T> strtofloatingpoint(const char *__restrict src) {
1129 using FPBits = typename fputil::FPBits<T>;
1130 using StorageType = typename FPBits::StorageType;
1131
1132 FPBits result = FPBits();
1133 bool seen_digit = false;
1134 char sign = '+';
1135
1136 int error = 0;
1137
1138 size_t index = static_cast<size_t>(first_non_whitespace(src) - src);
1139
1140 if (src[index] == '+' || src[index] == '-') {
1141 sign = src[index];
1142 ++index;
1143 }
1144
1145 if (sign == '-') {
1146 result.set_sign(Sign::NEG);
1147 }
1148
1149 static constexpr char DECIMAL_POINT = '.';
1150 static const char *inf_string = "infinity";
1151 static const char *nan_string = "nan";
1152
1153 if (isdigit(ch: src[index]) || src[index] == DECIMAL_POINT) { // regular number
1154 int base = 10;
1155 if (is_float_hex_start(src: src + index, decimalPoint: DECIMAL_POINT)) {
1156 base = 16;
1157 index += 2;
1158 seen_digit = true;
1159 }
1160
1161 RoundDirection round_direction = RoundDirection::Nearest;
1162
1163 switch (fputil::quick_get_round()) {
1164 case FE_TONEAREST:
1165 round_direction = RoundDirection::Nearest;
1166 break;
1167 case FE_UPWARD:
1168 if (sign == '+') {
1169 round_direction = RoundDirection::Up;
1170 } else {
1171 round_direction = RoundDirection::Down;
1172 }
1173 break;
1174 case FE_DOWNWARD:
1175 if (sign == '+') {
1176 round_direction = RoundDirection::Down;
1177 } else {
1178 round_direction = RoundDirection::Up;
1179 }
1180 break;
1181 case FE_TOWARDZERO:
1182 round_direction = RoundDirection::Down;
1183 break;
1184 }
1185
1186 StrToNumResult<ExpandedFloat<T>> parse_result({0, 0});
1187 if (base == 16) {
1188 parse_result = hexadecimal_string_to_float<T>(src + index, DECIMAL_POINT,
1189 round_direction);
1190 } else { // base is 10
1191 parse_result = decimal_string_to_float<T>(src + index, DECIMAL_POINT,
1192 round_direction);
1193 }
1194 seen_digit = parse_result.parsed_len != 0;
1195 result.set_mantissa(parse_result.value.mantissa);
1196 result.set_biased_exponent(parse_result.value.exponent);
1197 index += parse_result.parsed_len;
1198 error = parse_result.error;
1199 } else if (tolower(ch: src[index]) == 'n') { // NaN
1200 if (tolower(ch: src[index + 1]) == nan_string[1] &&
1201 tolower(ch: src[index + 2]) == nan_string[2]) {
1202 seen_digit = true;
1203 index += 3;
1204 StorageType nan_mantissa = 0;
1205 // this handles the case of `NaN(n-character-sequence)`, where the
1206 // n-character-sequence is made of 0 or more letters, numbers, or
1207 // underscore characters in any order.
1208 if (src[index] == '(') {
1209 size_t left_paren = index;
1210 ++index;
1211 while (isalnum(ch: src[index]) || src[index] == '_')
1212 ++index;
1213 if (src[index] == ')') {
1214 ++index;
1215 nan_mantissa = nan_mantissa_from_ncharseq<T>(
1216 cpp::string_view(src + (left_paren + 1), index - left_paren - 2));
1217 } else {
1218 index = left_paren;
1219 }
1220 }
1221 result = FPBits(result.quiet_nan(result.sign(), nan_mantissa));
1222 }
1223 } else if (tolower(ch: src[index]) == 'i') { // INF
1224 if (tolower(ch: src[index + 1]) == inf_string[1] &&
1225 tolower(ch: src[index + 2]) == inf_string[2]) {
1226 seen_digit = true;
1227 result = FPBits(result.inf(result.sign()));
1228 if (tolower(ch: src[index + 3]) == inf_string[3] &&
1229 tolower(ch: src[index + 4]) == inf_string[4] &&
1230 tolower(ch: src[index + 5]) == inf_string[5] &&
1231 tolower(ch: src[index + 6]) == inf_string[6] &&
1232 tolower(ch: src[index + 7]) == inf_string[7]) {
1233 // if the string is "INFINITY" then consume 8 characters.
1234 index += 8;
1235 } else {
1236 index += 3;
1237 }
1238 }
1239 }
1240 if (!seen_digit) { // If there is nothing to actually parse, then return 0.
1241 return {T(0), 0, error};
1242 }
1243
1244 // This function only does something if T is long double and the platform uses
1245 // special 80 bit long doubles. Otherwise it should be inlined out.
1246 set_implicit_bit<T>(result);
1247
1248 return {result.get_val(), static_cast<ptrdiff_t>(index), error};
1249}
1250
1251template <class T> LIBC_INLINE StrToNumResult<T> strtonan(const char *arg) {
1252 using FPBits = typename fputil::FPBits<T>;
1253 using StorageType = typename FPBits::StorageType;
1254
1255 LIBC_CRASH_ON_NULLPTR(arg);
1256
1257 FPBits result;
1258 int error = 0;
1259 StorageType nan_mantissa = 0;
1260
1261 ptrdiff_t index = 0;
1262 while (isalnum(ch: arg[index]) || arg[index] == '_')
1263 ++index;
1264
1265 if (arg[index] == '\0')
1266 nan_mantissa = nan_mantissa_from_ncharseq<T>(cpp::string_view(arg, index));
1267
1268 result = FPBits::quiet_nan(Sign::POS, nan_mantissa);
1269 return {result.get_val(), 0, error};
1270}
1271
1272} // namespace internal
1273} // namespace LIBC_NAMESPACE_DECL
1274
1275#endif // LLVM_LIBC_SRC___SUPPORT_STR_TO_FLOAT_H
1276