-
Notifications
You must be signed in to change notification settings - Fork 5.4k
/
Conv.h
1636 lines (1471 loc) · 49.5 KB
/
Conv.h
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
//
// Docs: https://fburl.com/fbcref_conv
//
/**
* Conv provides the ubiquitous method `to<TargetType>(source)`, along with
* a few other generic interfaces for converting objects to and from
* string-like types (std::string, fbstring, StringPiece), as well as
* range-checked conversions between numeric and enum types. The mechanisms are
* extensible, so that user-specified types can add folly::to support.
*
* folly::to<std::string>(123)
* // "123"
*
*******************************************************************************
* ## TYPE -> STRING CONVERSIONS
*******************************************************************************
* You can call the `to<std::string>` or `to<fbstring>`. These are variadic
* functions that convert their arguments to strings, and concatenate them to
* form a result. So, for example,
*
* auto str = to<std::string>(123, "456", 789);
*
* Sets str to `"123456789"`.
*
* In addition to just concatenating the arguments, related functions can
* delimit them with some string: `toDelim<std::string>(",", "123", 456, "789")`
* will return the string `"123,456,789"`.
*
* toAppend does not return a string; instead, it takes a pointer to a string as
* its last argument, and appends the result of the concatenation into it:
* std::string str = "123";
* toAppend(456, "789", &str); // Now str is "123456789".
*
* The toAppendFit function acts like toAppend, but it precalculates the size
* required to perform the append operation, and reserves that space in the
* output string before actually inserting its arguments. This can sometimes
* save on string expansion, but beware: appending to the same string many times
* with toAppendFit is likely a pessimization, since it will resize the string
* once per append.
*
* The combination of the append and delim variants also exist: toAppendDelim
* and toAppendDelimFit are defined, with the obvious semantics.
*
*******************************************************************************
* ## STRING -> TYPE CONVERSIONS
*******************************************************************************
* Going in the other direction, and parsing a string into a C++ type, is also
* supported:
* to<int>("123"); // Returns 123.
*
* Out of range (e.g. `to<std::uint8_t>("1000")`), or invalidly formatted (e.g.
* `to<int>("four")`) inputs will throw. If throw-on-error is undesirable (for
* instance: you're dealing with untrusted input, and want to protect yourself
* from users sending you down a very slow exception-throwing path), you can use
* `tryTo<T>`, which will return an `Expected<T, ConversionCode>`.
*
* There are overloads of to() and tryTo() that take a `StringPiece*`. These
* parse out a type from the beginning of a string, and modify the passed-in
* StringPiece to indicate the portion of the string not consumed.
*
*******************************************************************************
* ## NUMERIC / ENUM CONVERSIONS
*******************************************************************************
* Conv also supports a `to<T>(S)` overload, where T and S are numeric or enum
* types, that checks to see that the target type can represent its argument,
* and will throw if it cannot. This includes cases where a floating point to
* integral conversion is attempted on a value with a non-zero fractional
* component, and integral to floating point conversions that would lose
* precision. Enum conversions are range-checked for the underlying type of the
* enum, but there is no check that the input value is a valid choice of enum
* value.
*
*******************************************************************************
* ## CUSTOM TYPE CONVERSIONS
*******************************************************************************
* Users may customize the string conversion functionality for their own data
* types. The key functions you should implement are:
* // Two functions to allow conversion to your type from a string.
* Expected<StringPiece, ConversionCode> parseTo(folly::StringPiece in,
* YourType& out);
* YourErrorType makeConversionError(YourErrorType in, StringPiece in);
* // Two functions to allow conversion from your type to a string.
* template <class String>
* void toAppend(const YourType& in, String* out);
* size_t estimateSpaceNeeded(const YourType& in);
*
* These are documented below, inline.
*
* @file Conv.h
*/
#pragma once
#include <algorithm>
#include <cassert>
#include <cctype>
#include <climits>
#include <cmath>
#include <cstddef>
#include <limits>
#include <stdexcept>
#include <string>
#include <tuple>
#include <type_traits>
#include <utility>
#include <double-conversion/double-conversion.h> // V8 JavaScript implementation
#include <folly/CPortability.h>
#include <folly/Demangle.h>
#include <folly/Expected.h>
#include <folly/FBString.h>
#include <folly/Likely.h>
#include <folly/Portability.h>
#include <folly/Range.h>
#include <folly/Traits.h>
#include <folly/Unit.h>
#include <folly/Utility.h>
#include <folly/lang/Exception.h>
#include <folly/lang/Pretty.h>
#include <folly/lang/ToAscii.h>
#include <folly/portability/Math.h>
namespace folly {
// Keep this in sync with kErrorStrings in Conv.cpp
enum class ConversionCode : unsigned char {
SUCCESS,
EMPTY_INPUT_STRING,
NO_DIGITS,
BOOL_OVERFLOW,
BOOL_INVALID_VALUE,
NON_DIGIT_CHAR,
INVALID_LEADING_CHAR,
POSITIVE_OVERFLOW,
NEGATIVE_OVERFLOW,
STRING_TO_FLOAT_ERROR,
NON_WHITESPACE_AFTER_END,
ARITH_POSITIVE_OVERFLOW,
ARITH_NEGATIVE_OVERFLOW,
ARITH_LOSS_OF_PRECISION,
NUM_ERROR_CODES, // has to be the last entry
};
struct FOLLY_EXPORT ConversionErrorBase : std::range_error {
using std::range_error::range_error;
};
class FOLLY_EXPORT ConversionError : public ConversionErrorBase {
public:
ConversionError(const std::string& str, ConversionCode code)
: ConversionErrorBase(str), code_(code) {}
ConversionError(const char* str, ConversionCode code)
: ConversionErrorBase(str), code_(code) {}
ConversionCode errorCode() const { return code_; }
private:
ConversionCode code_;
};
/**
* Custom Error Translation
*
* Your overloaded parseTo() function can return a custom error code on failure.
* ::folly::to() will call makeConversionError to translate that error code into
* an object to throw. makeConversionError is found by argument-dependent
* lookup. It should have this signature:
*
* namespace other_namespace {
* enum YourErrorCode { BAD_ERROR, WORSE_ERROR };
*
* struct YourConversionError : ConversionErrorBase {
* YourConversionError(const char* what) : ConversionErrorBase(what) {}
* };
*
* YourConversionError
* makeConversionError(YourErrorCode code, ::folly::StringPiece sp) {
* ...
* return YourConversionError(messageString);
* }
*/
ConversionError makeConversionError(ConversionCode code, StringPiece input);
namespace detail {
/**
* Enforce that the suffix following a number is made up only of whitespace.
*/
inline ConversionCode enforceWhitespaceErr(StringPiece sp) {
for (auto c : sp) {
if (FOLLY_UNLIKELY(!std::isspace(c))) {
return ConversionCode::NON_WHITESPACE_AFTER_END;
}
}
return ConversionCode::SUCCESS;
}
/**
* Keep this implementation around for prettyToDouble().
*/
inline void enforceWhitespace(StringPiece sp) {
auto err = enforceWhitespaceErr(sp);
if (err != ConversionCode::SUCCESS) {
throw_exception(makeConversionError(err, sp));
}
}
} // namespace detail
/**
* @overloadbrief to, but return an Expected
*
* The identity conversion function.
* tryTo<T>(T) returns itself for all types T.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_same<Tgt, typename std::decay<Src>::type>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(Src&& value) {
return static_cast<Src&&>(value);
}
/**
* @overloadbrief Convert from one type to another.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_same<Tgt, typename std::decay<Src>::type>::value,
Tgt>::type
to(Src&& value) {
return static_cast<Src&&>(value);
}
/**
* Arithmetic to boolean
*/
/**
* Unchecked conversion from arithmetic to boolean. This is different from the
* other arithmetic conversions because we use the C convention of treating any
* non-zero value as true, instead of range checking.
*/
template <class Tgt, class Src>
typename std::enable_if<
is_arithmetic_v<Src> && !std::is_same<Tgt, Src>::value &&
std::is_same<Tgt, bool>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(const Src& value) {
return value != Src();
}
template <class Tgt, class Src>
typename std::enable_if<
is_arithmetic_v<Src> && !std::is_same<Tgt, Src>::value &&
std::is_same<Tgt, bool>::value,
Tgt>::type
to(const Src& value) {
return value != Src();
}
/**
* Anything to string
*/
namespace detail {
template <class... T>
using LastElement = type_pack_element_t<sizeof...(T) - 1, T...>;
#ifdef _MSC_VER
// MSVC can't quite figure out the LastElementImpl::call() stuff
// in the base implementation, so we have to use tuples instead,
// which result in significantly more templates being compiled,
// though the runtime performance is the same.
template <typename... Ts, typename R = LastElement<Ts...>>
const R& getLastElement(const Ts&... ts) {
return std::get<sizeof...(Ts) - 1>(std::forward_as_tuple(ts...));
}
inline void getLastElement() {}
#else
template <typename...>
struct LastElementImpl;
template <>
struct LastElementImpl<> {
static void call() {}
};
template <typename Ign, typename... Igns>
struct LastElementImpl<Ign, Igns...> {
template <typename Last>
static const Last& call(Igns..., const Last& last) {
return last;
}
};
template <typename... Ts, typename R = LastElement<Ts...>>
const R& getLastElement(const Ts&... ts) {
return LastElementImpl<Ignored<Ts>...>::call(ts...);
}
#endif
} // namespace detail
/**
* Conversions from integral types to string types.
*/
#if FOLLY_HAVE_INT128_T
namespace detail {
template <typename IntegerType>
constexpr unsigned int digitsEnough() {
// digits10 returns the number of decimal digits that this type can represent,
// not the number of characters required for the max value, so we need to add
// one. ex: char digits10 returns 2, because 256-999 cannot be represented,
// but we need 3.
auto const digits10 = std::numeric_limits<IntegerType>::digits10;
return static_cast<unsigned int>(digits10) + 1;
}
inline size_t unsafeTelescope128(char* outb, char* oute, unsigned __int128 x) {
using Usrc = unsigned __int128;
// Decompose the input into at most 3 components using the largest power-of-10
// base that fits in a 64-bit unsigned integer, and then convert the
// components using 64-bit arithmetic and concatenate them.
constexpr static auto kBase = UINT64_C(10'000'000'000'000'000'000);
constexpr static size_t kBaseDigits = 19;
size_t p = 0;
const auto leading = [&](Usrc v) {
assert(v >> 64 == 0);
p = detail::to_ascii_with_route<10, to_ascii_alphabet_lower>(
outb, oute, static_cast<uint64_t>(v));
};
const auto append = [&](uint64_t v) {
assert(v < kBase);
assert(outb + p + kBaseDigits <= oute);
auto v64 = static_cast<uint64_t>(v);
detail::to_ascii_with_route<10, to_ascii_alphabet_lower>(
outb + p, kBaseDigits, v64);
p += kBaseDigits;
};
if (x >> 64 > 0) {
const auto rem = static_cast<uint64_t>(x % kBase);
x /= kBase;
if (x >> 64 > 0) {
const auto rem2 = static_cast<uint64_t>(x % kBase);
x /= kBase;
leading(x);
append(rem2);
append(rem);
return p;
}
leading(x);
append(rem);
return p;
}
leading(x);
return p;
}
} // namespace detail
#endif
/**
* @overloadbrief Appends conversion to string.
*
* A single char gets appended.
*/
template <class Tgt>
void toAppend(char value, Tgt* result) {
*result += value;
}
/**
* @overloadbrief Estimates the number of characters in a value's string
* representation.
*/
template <class T>
constexpr typename std::enable_if<std::is_same<T, char>::value, size_t>::type
estimateSpaceNeeded(T) {
return 1;
}
template <size_t N>
constexpr size_t estimateSpaceNeeded(const char (&)[N]) {
return N;
}
/**
* Everything implicitly convertible to const char* gets appended.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_convertible<Src, const char*>::value &&
IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt* result) {
// Treat null pointers like an empty string, as in:
// operator<<(std::ostream&, const char*).
const char* c = value;
if (c) {
result->append(value);
}
}
template <class Src>
typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
type
estimateSpaceNeeded(Src value) {
const char* c = value;
return c ? std::strlen(c) : 0;
}
template <class Src>
typename std::enable_if<IsSomeString<Src>::value, size_t>::type
estimateSpaceNeeded(Src const& value) {
return value.size();
}
template <class Src>
typename std::enable_if<
std::is_convertible<Src, folly::StringPiece>::value &&
!IsSomeString<Src>::value &&
!std::is_convertible<Src, const char*>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
return folly::StringPiece(value).size();
}
template <>
inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
return 0;
}
template <class Src>
typename std::enable_if<
std::is_pointer<Src>::value &&
IsSomeString<std::remove_pointer<Src>>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
return value->size();
}
/**
* Strings get appended, too.
*/
template <class Tgt, class Src>
typename std::enable_if<
IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(const Src& value, Tgt* result) {
result->append(value);
}
/**
* and StringPiece objects too
*/
template <class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
StringPiece value, Tgt* result) {
result->append(value.data(), value.size());
}
/**
* There's no implicit conversion from fbstring to other string types,
* so make a specialization.
*/
template <class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
const fbstring& value, Tgt* result) {
result->append(value.data(), value.size());
}
#if FOLLY_HAVE_INT128_T
/**
* Special handling for 128 bit integers.
*/
template <class Tgt>
void toAppend(__int128 value, Tgt* result) {
typedef unsigned __int128 Usrc;
char buffer[detail::digitsEnough<unsigned __int128>() + 1];
const auto oute = buffer + sizeof(buffer);
size_t p;
if (value < 0) {
buffer[0] = '-';
p = 1 + detail::unsafeTelescope128(buffer + 1, oute, -Usrc(value));
} else {
p = detail::unsafeTelescope128(buffer, oute, value);
}
result->append(buffer, p);
}
template <class Tgt>
void toAppend(unsigned __int128 value, Tgt* result) {
char buffer[detail::digitsEnough<unsigned __int128>()];
size_t p = detail::unsafeTelescope128(buffer, buffer + sizeof(buffer), value);
result->append(buffer, p);
}
template <class T>
constexpr
typename std::enable_if<std::is_same<T, __int128>::value, size_t>::type
estimateSpaceNeeded(T) {
return detail::digitsEnough<__int128>();
}
template <class T>
constexpr typename std::
enable_if<std::is_same<T, unsigned __int128>::value, size_t>::type
estimateSpaceNeeded(T) {
return detail::digitsEnough<unsigned __int128>();
}
#endif
/**
* int32_t and int64_t to string (by appending) go through here. The
* result is APPENDED to a preexisting string passed as the second
* parameter. This should be efficient with fbstring because fbstring
* incurs no dynamic allocation below 23 bytes and no number has more
* than 22 bytes in its textual representation (20 for digits, one for
* sign, one for the terminating 0).
*/
template <class Tgt, class Src>
typename std::enable_if<
is_integral_v<Src> && is_signed_v<Src> && IsSomeString<Tgt>::value &&
sizeof(Src) >= 4>::type
toAppend(Src value, Tgt* result) {
char buffer[to_ascii_size_max_decimal<uint64_t>];
auto uvalue = value < 0 ? ~static_cast<uint64_t>(value) + 1
: static_cast<uint64_t>(value);
if (value < 0) {
result->push_back('-');
}
result->append(buffer, to_ascii_decimal(buffer, uvalue));
}
template <class Src>
typename std::enable_if<
is_integral_v<Src> && is_signed_v<Src> && sizeof(Src) >= 4 &&
sizeof(Src) < 16,
size_t>::type
estimateSpaceNeeded(Src value) {
auto uvalue = value < 0 ? ~static_cast<uint64_t>(value) + 1
: static_cast<uint64_t>(value);
return size_t(value < 0) + to_ascii_size_decimal(uvalue);
}
/**
* As above, but for uint32_t and uint64_t.
*/
template <class Tgt, class Src>
typename std::enable_if<
is_integral_v<Src> && !is_signed_v<Src> && IsSomeString<Tgt>::value &&
sizeof(Src) >= 4>::type
toAppend(Src value, Tgt* result) {
char buffer[to_ascii_size_max_decimal<uint64_t>];
result->append(buffer, to_ascii_decimal(buffer, value));
}
template <class Src>
typename std::enable_if<
is_integral_v<Src> && !is_signed_v<Src> && sizeof(Src) >= 4 &&
sizeof(Src) < 16,
size_t>::type
estimateSpaceNeeded(Src value) {
return to_ascii_size_decimal(value);
}
/**
* All small signed and unsigned integers to string go through 32-bit
* types int32_t and uint32_t, respectively.
*/
template <class Tgt, class Src>
typename std::enable_if<
is_integral_v<Src> && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
toAppend(Src value, Tgt* result) {
typedef typename std::conditional<is_signed_v<Src>, int64_t, uint64_t>::type
Intermediate;
toAppend<Tgt>(static_cast<Intermediate>(value), result);
}
template <class Src>
typename std::enable_if<
is_integral_v<Src> && sizeof(Src) < 4 && !std::is_same<Src, char>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
typedef typename std::conditional<is_signed_v<Src>, int64_t, uint64_t>::type
Intermediate;
return estimateSpaceNeeded(static_cast<Intermediate>(value));
}
/**
* Enumerated values get appended as integers.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt* result) {
toAppend(to_underlying(value), result);
}
template <class Src>
typename std::enable_if<std::is_enum<Src>::value, size_t>::type
estimateSpaceNeeded(Src value) {
return estimateSpaceNeeded(to_underlying(value));
}
/**
* Conversions from floating-point types to string types.
*/
namespace detail {
constexpr int kConvMaxDecimalInShortestLow = -6;
constexpr int kConvMaxDecimalInShortestHigh = 21;
} // namespace detail
/** Wrapper around DoubleToStringConverter */
template <class Tgt, class Src>
typename std::enable_if<
std::is_floating_point<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(
Src value,
Tgt* result,
double_conversion::DoubleToStringConverter::DtoaMode mode,
unsigned int numDigits,
double_conversion::DoubleToStringConverter::Flags flags =
double_conversion::DoubleToStringConverter::NO_FLAGS) {
using namespace double_conversion;
DoubleToStringConverter conv(
flags,
"Infinity",
"NaN",
'E',
detail::kConvMaxDecimalInShortestLow,
detail::kConvMaxDecimalInShortestHigh,
6, // max leading padding zeros
1); // max trailing padding zeros
char buffer[256];
StringBuilder builder(buffer, sizeof(buffer));
FOLLY_PUSH_WARNING
FOLLY_CLANG_DISABLE_WARNING("-Wcovered-switch-default")
switch (mode) {
case DoubleToStringConverter::SHORTEST:
conv.ToShortest(value, &builder);
break;
case DoubleToStringConverter::SHORTEST_SINGLE:
conv.ToShortestSingle(static_cast<float>(value), &builder);
break;
case DoubleToStringConverter::FIXED:
conv.ToFixed(value, int(numDigits), &builder);
break;
case DoubleToStringConverter::PRECISION:
default:
assert(mode == DoubleToStringConverter::PRECISION);
conv.ToPrecision(value, int(numDigits), &builder);
break;
}
FOLLY_POP_WARNING
const size_t length = size_t(builder.position());
builder.Finalize();
result->append(buffer, length);
}
/**
* As above, but for floating point
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_floating_point<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt* result) {
toAppend(
value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
}
/**
* Upper bound of the length of the output from
* DoubleToStringConverter::ToShortest(double, StringBuilder*),
* as used in toAppend(double, string*).
*/
template <class Src>
typename std::enable_if<std::is_floating_point<Src>::value, size_t>::type
estimateSpaceNeeded(Src value) {
// kBase10MaximalLength is 17. We add 1 for decimal point,
// e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
constexpr int kMaxMantissaSpace =
double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
// strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
constexpr int kMaxExponentSpace = 2 + 3;
static const int kMaxPositiveSpace = std::max({
// E.g. 1.1111111111111111E-100.
kMaxMantissaSpace + kMaxExponentSpace,
// E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
// If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
// number > 1 which ToShortest outputs in exponential notation,
// so 21 is the longest non-exponential number > 1.
detail::kConvMaxDecimalInShortestHigh,
});
return size_t(
kMaxPositiveSpace +
(value < 0 ? 1 : 0)); // +1 for minus sign, if negative
}
template <class Src>
constexpr typename std::enable_if<
!std::is_fundamental<Src>::value &&
#if FOLLY_HAVE_INT128_T
// On OSX 10.10, is_fundamental<__int128> is false :-O
!std::is_same<__int128, Src>::value &&
!std::is_same<unsigned __int128, Src>::value &&
#endif
!IsSomeString<Src>::value &&
!std::is_convertible<Src, const char*>::value &&
!std::is_convertible<Src, StringPiece>::value &&
!std::is_enum<Src>::value,
size_t>::type
estimateSpaceNeeded(const Src&) {
return sizeof(Src) + 1; // dumbest best effort ever?
}
#ifndef DOXYGEN_SHOULD_SKIP_THIS
namespace detail {
FOLLY_ERASE constexpr size_t estimateSpaceToReserveOne(std::false_type, void*) {
return 0;
}
template <typename T>
FOLLY_ERASE constexpr size_t estimateSpaceToReserveOne(
std::true_type, const T& v) {
return estimateSpaceNeeded(v);
}
template <typename>
struct EstimateSpaceToReserveAll;
template <size_t... I>
struct EstimateSpaceToReserveAll<std::index_sequence<I...>> {
template <size_t J, size_t N = sizeof...(I)>
using tag = std::bool_constant<J + 1 < N>;
template <class... T>
static size_t call(const T&... v) {
const size_t sizes[] = {estimateSpaceToReserveOne(tag<I>{}, v)...};
size_t size = 0;
for (const auto s : sizes) {
size += s;
}
return size;
}
};
template <class O>
void reserveInTarget(const O& o) {
(void)o;
}
template <class T, class O>
void reserveInTarget(const T& v, const O& o) {
o->reserve(estimateSpaceNeeded(v));
}
template <class T0, class T1, class... Ts>
void reserveInTarget(const T0& v0, const T1& v1, const Ts&... vs) {
using seq = std::index_sequence_for<T0, T1, Ts...>;
getLastElement(vs...)->reserve(
EstimateSpaceToReserveAll<seq>::call(v0, v1, vs...));
}
template <class Delimiter, class... Ts>
void reserveInTargetDelim(const Delimiter& d, const Ts&... vs) {
static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
using seq = std::index_sequence_for<Ts...>;
size_t fordelim = (sizeof...(vs) - 2) * estimateSpaceNeeded(d);
getLastElement(vs...)->reserve(
fordelim + EstimateSpaceToReserveAll<seq>::call(vs...));
}
template <class T>
FOLLY_ERASE constexpr int toAppendStrImplOne(
std::false_type, const T& v, void*) {
(void)v;
return 0;
}
template <class T, class Tgt>
FOLLY_ERASE int toAppendStrImplOne(std::true_type, const T& v, Tgt result) {
return toAppend(v, result), 0;
}
template <typename>
struct ToAppendStrImplAll;
template <size_t... I>
struct ToAppendStrImplAll<std::index_sequence<I...>> {
template <class... T>
static void call(const T&... v) {
using _ = int[];
auto r = getLastElement(v...);
void(_{toAppendStrImplOne(
std::bool_constant<I + 1 < sizeof...(T)>{}, v, r)...});
}
};
template <class Delimiter, class T>
FOLLY_ERASE constexpr int toAppendDelimStrImplOne(
index_constant<0>, const Delimiter& d, const T& v, void*) {
(void)d;
(void)v;
return 0;
}
template <class Delimiter, class T, class Tgt>
FOLLY_ERASE int toAppendDelimStrImplOne(
index_constant<1>, const Delimiter& d, const T& v, Tgt result) {
(void)d;
toAppend(v, result);
return 0;
}
template <class Delimiter, class T, class Tgt>
FOLLY_ERASE int toAppendDelimStrImplOne(
index_constant<2>, const Delimiter& d, const T& v, Tgt result) {
toAppend(v, result);
toAppend(d, result);
return 0;
}
template <typename>
struct ToAppendDelimStrImplAll;
template <size_t... I>
struct ToAppendDelimStrImplAll<std::index_sequence<I...>> {
template <size_t J, size_t N = sizeof...(I), size_t K = N - J - 1>
using tag = index_constant<(K < 2 ? K : 2)>;
template <class Delimiter, class... T>
static void call(const Delimiter& d, const T&... v) {
using _ = int[];
auto r = detail::getLastElement(v...);
void(_{toAppendDelimStrImplOne(tag<I>{}, d, v, r)...});
}
};
template <
class Delimiter,
class T,
class... Ts,
std::enable_if_t<
sizeof...(Ts) >= 2 &&
IsSomeString<typename std::remove_pointer<
detail::LastElement<Ts...>>::type>::value,
int> = 0>
void toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
using seq = std::index_sequence_for<T, Ts...>;
ToAppendDelimStrImplAll<seq>::call(delim, v, vs...);
}
} // namespace detail
#endif
/**
* Variadic conversion to string. Appends each element in turn.
* If we have two or more things to append, we will not reserve
* the space for them and will depend on strings exponential growth.
* If you just append once consider using toAppendFit which reserves
* the space needed (but does not have exponential as a result).
*
* Custom implementations of toAppend() can be provided in the same namespace as
* the type to customize printing. estimateSpaceNeed() may also be provided to
* avoid reallocations in toAppendFit():
*
* namespace other_namespace {
*
* template <class String>
* void toAppend(const OtherType&, String* out);
*
* // optional
* size_t estimateSpaceNeeded(const OtherType&);
*
* }
*/
template <
class... Ts,
std::enable_if_t<
sizeof...(Ts) >= 3 &&
IsSomeString<typename std::remove_pointer<
detail::LastElement<Ts...>>::type>::value,
int> = 0>
void toAppend(const Ts&... vs) {
using seq = std::index_sequence_for<Ts...>;
detail::ToAppendStrImplAll<seq>::call(vs...);
}
/**
* @overloadbrief toAppend, but pre-allocate the exact amount of space required.
*
* Special version of the call that preallocates exactly as much memory
* as need for arguments to be stored in target. This means we are
* not doing exponential growth when we append. If you are using it
* in a loop you are aiming at your foot with a big perf-destroying
* bazooka.
* On the other hand if you are appending to a string once, this
* will probably save a few calls to malloc.
*/
template <
class... Ts,
std::enable_if_t<
IsSomeString<typename std::remove_pointer<
detail::LastElement<Ts...>>::type>::value,
int> = 0>
void toAppendFit(const Ts&... vs) {
::folly::detail::reserveInTarget(vs...);
toAppend(vs...);
}
template <class Ts>
void toAppendFit(const Ts&) {}
/**
* Variadic base case: do nothing.
*/
template <class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
Tgt* /* result */) {}
/**
* @overloadbrief Use a specified delimiter between appendees.
*
* Variadic base case: do nothing.
*/
template <class Delimiter, class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
const Delimiter& /* delim */, Tgt* /* result */) {}
/**
* 1 element: same as toAppend.
*/
template <class Delimiter, class T, class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
const Delimiter& /* delim */, const T& v, Tgt* tgt) {
toAppend(v, tgt);
}
/**
* Append to string with a delimiter in between elements. Check out
* comments for toAppend for details about memory allocation.
*/
template <
class Delimiter,
class... Ts,
std::enable_if_t<
sizeof...(Ts) >= 3 &&
IsSomeString<typename std::remove_pointer<
detail::LastElement<Ts...>>::type>::value,
int> = 0>
void toAppendDelim(const Delimiter& delim, const Ts&... vs) {
detail::toAppendDelimStrImpl(delim, vs...);
}
/**
* @overloadbrief toAppend with custom delimiter and exact pre-allocation.
*
* Detail in comment for toAppendFit
*/
template <
class Delimiter,
class... Ts,
std::enable_if_t<
IsSomeString<typename std::remove_pointer<
detail::LastElement<Ts...>>::type>::value,
int> = 0>
void toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
detail::reserveInTargetDelim(delim, vs...);
toAppendDelim(delim, vs...);
}
template <class De, class Ts>
void toAppendDelimFit(const De&, const Ts&) {}
/**
* to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
* for all types.
*/
template <
class Tgt,