summaryrefslogtreecommitdiff
path: root/absl/time/time.h
blob: 61fa159b9e814096a00f4c4ba4cbac69809150a2 (plain)
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
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
// Copyright 2017 The Abseil Authors.
//
// 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
//
//      https://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.
//
// -----------------------------------------------------------------------------
// File: time.h
// -----------------------------------------------------------------------------
//
// This header file defines abstractions for computing with absolute points
// in time, durations of time, and formatting and parsing time within a given
// time zone. The following abstractions are defined:
//
//  * `absl::Time` defines an absolute, specific instance in time
//  * `absl::Duration` defines a signed, fixed-length span of time
//  * `absl::TimeZone` defines geopolitical time zone regions (as collected
//     within the IANA Time Zone database (https://www.iana.org/time-zones)).
//
// Note: Absolute times are distinct from civil times, which refer to the
// human-scale time commonly represented by `YYYY-MM-DD hh:mm:ss`. The mapping
// between absolute and civil times can be specified by use of time zones
// (`absl::TimeZone` within this API). That is:
//
//   Civil Time = F(Absolute Time, Time Zone)
//   Absolute Time = G(Civil Time, Time Zone)
//
// See civil_time.h for abstractions related to constructing and manipulating
// civil time.
//
// Example:
//
//   absl::TimeZone nyc;
//   // LoadTimeZone() may fail so it's always better to check for success.
//   if (!absl::LoadTimeZone("America/New_York", &nyc)) {
//      // handle error case
//   }
//
//   // My flight leaves NYC on Jan 2, 2017 at 03:04:05
//   absl::CivilSecond cs(2017, 1, 2, 3, 4, 5);
//   absl::Time takeoff = absl::FromCivil(cs, nyc);
//
//   absl::Duration flight_duration = absl::Hours(21) + absl::Minutes(35);
//   absl::Time landing = takeoff + flight_duration;
//
//   absl::TimeZone syd;
//   if (!absl::LoadTimeZone("Australia/Sydney", &syd)) {
//      // handle error case
//   }
//   std::string s = absl::FormatTime(
//       "My flight will land in Sydney on %Y-%m-%d at %H:%M:%S",
//       landing, syd);

#ifndef ABSL_TIME_TIME_H_
#define ABSL_TIME_TIME_H_

#if !defined(_MSC_VER)
#include <sys/time.h>
#else
// We don't include `winsock2.h` because it drags in `windows.h` and friends,
// and they define conflicting macros like OPAQUE, ERROR, and more. This has the
// potential to break Abseil users.
//
// Instead we only forward declare `timeval` and require Windows users include
// `winsock2.h` themselves. This is both inconsistent and troublesome, but so is
// including 'windows.h' so we are picking the lesser of two evils here.
struct timeval;
#endif
#include <chrono>  // NOLINT(build/c++11)
#include <cmath>
#include <cstdint>
#include <ctime>
#include <ostream>
#include <string>
#include <type_traits>
#include <utility>

#include "absl/base/macros.h"
#include "absl/strings/string_view.h"
#include "absl/time/civil_time.h"
#include "absl/time/internal/cctz/include/cctz/time_zone.h"

namespace absl {
ABSL_NAMESPACE_BEGIN

class Duration;  // Defined below
class Time;      // Defined below
class TimeZone;  // Defined below

namespace time_internal {
int64_t IDivDuration(bool satq, Duration num, Duration den, Duration* rem);
constexpr Time FromUnixDuration(Duration d);
constexpr Duration ToUnixDuration(Time t);
constexpr int64_t GetRepHi(Duration d);
constexpr uint32_t GetRepLo(Duration d);
constexpr Duration MakeDuration(int64_t hi, uint32_t lo);
constexpr Duration MakeDuration(int64_t hi, int64_t lo);
inline Duration MakePosDoubleDuration(double n);
constexpr int64_t kTicksPerNanosecond = 4;
constexpr int64_t kTicksPerSecond = 1000 * 1000 * 1000 * kTicksPerNanosecond;
template <std::intmax_t N>
constexpr Duration FromInt64(int64_t v, std::ratio<1, N>);
constexpr Duration FromInt64(int64_t v, std::ratio<60>);
constexpr Duration FromInt64(int64_t v, std::ratio<3600>);
template <typename T>
using EnableIfIntegral = typename std::enable_if<
    std::is_integral<T>::value || std::is_enum<T>::value, int>::type;
template <typename T>
using EnableIfFloat =
    typename std::enable_if<std::is_floating_point<T>::value, int>::type;
}  // namespace time_internal

// Duration
//
// The `absl::Duration` class represents a signed, fixed-length amount of time.
// A `Duration` is generated using a unit-specific factory function, or is
// the result of subtracting one `absl::Time` from another. Durations behave
// like unit-safe integers and they support all the natural integer-like
// arithmetic operations. Arithmetic overflows and saturates at +/- infinity.
// `Duration` should be passed by value rather than const reference.
//
// Factory functions `Nanoseconds()`, `Microseconds()`, `Milliseconds()`,
// `Seconds()`, `Minutes()`, `Hours()` and `InfiniteDuration()` allow for
// creation of constexpr `Duration` values
//
// Examples:
//
//   constexpr absl::Duration ten_ns = absl::Nanoseconds(10);
//   constexpr absl::Duration min = absl::Minutes(1);
//   constexpr absl::Duration hour = absl::Hours(1);
//   absl::Duration dur = 60 * min;  // dur == hour
//   absl::Duration half_sec = absl::Milliseconds(500);
//   absl::Duration quarter_sec = 0.25 * absl::Seconds(1);
//
// `Duration` values can be easily converted to an integral number of units
// using the division operator.
//
// Example:
//
//   constexpr absl::Duration dur = absl::Milliseconds(1500);
//   int64_t ns = dur / absl::Nanoseconds(1);   // ns == 1500000000
//   int64_t ms = dur / absl::Milliseconds(1);  // ms == 1500
//   int64_t sec = dur / absl::Seconds(1);    // sec == 1 (subseconds truncated)
//   int64_t min = dur / absl::Minutes(1);    // min == 0
//
// See the `IDivDuration()` and `FDivDuration()` functions below for details on
// how to access the fractional parts of the quotient.
//
// Alternatively, conversions can be performed using helpers such as
// `ToInt64Microseconds()` and `ToDoubleSeconds()`.
class Duration {
 public:
  // Value semantics.
  constexpr Duration() : rep_hi_(0), rep_lo_(0) {}  // zero-length duration

  // Copyable.
#if !defined(__clang__) && defined(_MSC_VER) && _MSC_VER < 1910
  // Explicitly defining the constexpr copy constructor avoids an MSVC bug.
  constexpr Duration(const Duration& d)
      : rep_hi_(d.rep_hi_), rep_lo_(d.rep_lo_) {}
#else
  constexpr Duration(const Duration& d) = default;
#endif
  Duration& operator=(const Duration& d) = default;

  // Compound assignment operators.
  Duration& operator+=(Duration d);
  Duration& operator-=(Duration d);
  Duration& operator*=(int64_t r);
  Duration& operator*=(double r);
  Duration& operator/=(int64_t r);
  Duration& operator/=(double r);
  Duration& operator%=(Duration rhs);

  // Overloads that forward to either the int64_t or double overloads above.
  // Integer operands must be representable as int64_t.
  template <typename T, time_internal::EnableIfIntegral<T> = 0>
  Duration& operator*=(T r) {
    int64_t x = r;
    return *this *= x;
  }

  template <typename T, time_internal::EnableIfIntegral<T> = 0>
  Duration& operator/=(T r) {
    int64_t x = r;
    return *this /= x;
  }

  template <typename T, time_internal::EnableIfFloat<T> = 0>
  Duration& operator*=(T r) {
    double x = r;
    return *this *= x;
  }

  template <typename T, time_internal::EnableIfFloat<T> = 0>
  Duration& operator/=(T r) {
    double x = r;
    return *this /= x;
  }

  template <typename H>
  friend H AbslHashValue(H h, Duration d) {
    return H::combine(std::move(h), d.rep_hi_, d.rep_lo_);
  }

 private:
  friend constexpr int64_t time_internal::GetRepHi(Duration d);
  friend constexpr uint32_t time_internal::GetRepLo(Duration d);
  friend constexpr Duration time_internal::MakeDuration(int64_t hi,
                                                        uint32_t lo);
  constexpr Duration(int64_t hi, uint32_t lo) : rep_hi_(hi), rep_lo_(lo) {}
  int64_t rep_hi_;
  uint32_t rep_lo_;
};

// Relational Operators
constexpr bool operator<(Duration lhs, Duration rhs);
constexpr bool operator>(Duration lhs, Duration rhs) { return rhs < lhs; }
constexpr bool operator>=(Duration lhs, Duration rhs) { return !(lhs < rhs); }
constexpr bool operator<=(Duration lhs, Duration rhs) { return !(rhs < lhs); }
constexpr bool operator==(Duration lhs, Duration rhs);
constexpr bool operator!=(Duration lhs, Duration rhs) { return !(lhs == rhs); }

// Additive Operators
constexpr Duration operator-(Duration d);
inline Duration operator+(Duration lhs, Duration rhs) { return lhs += rhs; }
inline Duration operator-(Duration lhs, Duration rhs) { return lhs -= rhs; }

// Multiplicative Operators
// Integer operands must be representable as int64_t.
template <typename T>
Duration operator*(Duration lhs, T rhs) {
  return lhs *= rhs;
}
template <typename T>
Duration operator*(T lhs, Duration rhs) {
  return rhs *= lhs;
}
template <typename T>
Duration operator/(Duration lhs, T rhs) {
  return lhs /= rhs;
}
inline int64_t operator/(Duration lhs, Duration rhs) {
  return time_internal::IDivDuration(true, lhs, rhs,
                                     &lhs);  // trunc towards zero
}
inline Duration operator%(Duration lhs, Duration rhs) { return lhs %= rhs; }

// IDivDuration()
//
// Divides a numerator `Duration` by a denominator `Duration`, returning the
// quotient and remainder. The remainder always has the same sign as the
// numerator. The returned quotient and remainder respect the identity:
//
//   numerator = denominator * quotient + remainder
//
// Returned quotients are capped to the range of `int64_t`, with the difference
// spilling into the remainder to uphold the above identity. This means that the
// remainder returned could differ from the remainder returned by
// `Duration::operator%` for huge quotients.
//
// See also the notes on `InfiniteDuration()` below regarding the behavior of
// division involving zero and infinite durations.
//
// Example:
//
//   constexpr absl::Duration a =
//       absl::Seconds(std::numeric_limits<int64_t>::max());  // big
//   constexpr absl::Duration b = absl::Nanoseconds(1);       // small
//
//   absl::Duration rem = a % b;
//   // rem == absl::ZeroDuration()
//
//   // Here, q would overflow int64_t, so rem accounts for the difference.
//   int64_t q = absl::IDivDuration(a, b, &rem);
//   // q == std::numeric_limits<int64_t>::max(), rem == a - b * q
inline int64_t IDivDuration(Duration num, Duration den, Duration* rem) {
  return time_internal::IDivDuration(true, num, den,
                                     rem);  // trunc towards zero
}

// FDivDuration()
//
// Divides a `Duration` numerator into a fractional number of units of a
// `Duration` denominator.
//
// See also the notes on `InfiniteDuration()` below regarding the behavior of
// division involving zero and infinite durations.
//
// Example:
//
//   double d = absl::FDivDuration(absl::Milliseconds(1500), absl::Seconds(1));
//   // d == 1.5
double FDivDuration(Duration num, Duration den);

// ZeroDuration()
//
// Returns a zero-length duration. This function behaves just like the default
// constructor, but the name helps make the semantics clear at call sites.
constexpr Duration ZeroDuration() { return Duration(); }

// AbsDuration()
//
// Returns the absolute value of a duration.
inline Duration AbsDuration(Duration d) {
  return (d < ZeroDuration()) ? -d : d;
}

// Trunc()
//
// Truncates a duration (toward zero) to a multiple of a non-zero unit.
//
// Example:
//
//   absl::Duration d = absl::Nanoseconds(123456789);
//   absl::Duration a = absl::Trunc(d, absl::Microseconds(1));  // 123456us
Duration Trunc(Duration d, Duration unit);

// Floor()
//
// Floors a duration using the passed duration unit to its largest value not
// greater than the duration.
//
// Example:
//
//   absl::Duration d = absl::Nanoseconds(123456789);
//   absl::Duration b = absl::Floor(d, absl::Microseconds(1));  // 123456us
Duration Floor(Duration d, Duration unit);

// Ceil()
//
// Returns the ceiling of a duration using the passed duration unit to its
// smallest value not less than the duration.
//
// Example:
//
//   absl::Duration d = absl::Nanoseconds(123456789);
//   absl::Duration c = absl::Ceil(d, absl::Microseconds(1));   // 123457us
Duration Ceil(Duration d, Duration unit);

// InfiniteDuration()
//
// Returns an infinite `Duration`.  To get a `Duration` representing negative
// infinity, use `-InfiniteDuration()`.
//
// Duration arithmetic overflows to +/- infinity and saturates. In general,
// arithmetic with `Duration` infinities is similar to IEEE 754 infinities
// except where IEEE 754 NaN would be involved, in which case +/-
// `InfiniteDuration()` is used in place of a "nan" Duration.
//
// Examples:
//
//   constexpr absl::Duration inf = absl::InfiniteDuration();
//   const absl::Duration d = ... any finite duration ...
//
//   inf == inf + inf
//   inf == inf + d
//   inf == inf - inf
//   -inf == d - inf
//
//   inf == d * 1e100
//   inf == inf / 2
//   0 == d / inf
//   INT64_MAX == inf / d
//
//   d < inf
//   -inf < d
//
//   // Division by zero returns infinity, or INT64_MIN/MAX where appropriate.
//   inf == d / 0
//   INT64_MAX == d / absl::ZeroDuration()
//
// The examples involving the `/` operator above also apply to `IDivDuration()`
// and `FDivDuration()`.
constexpr Duration InfiniteDuration();

// Nanoseconds()
// Microseconds()
// Milliseconds()
// Seconds()
// Minutes()
// Hours()
//
// Factory functions for constructing `Duration` values from an integral number
// of the unit indicated by the factory function's name. The number must be
// representable as int64_t.
//
// NOTE: no "Days()" factory function exists because "a day" is ambiguous.
// Civil days are not always 24 hours long, and a 24-hour duration often does
// not correspond with a civil day. If a 24-hour duration is needed, use
// `absl::Hours(24)`. If you actually want a civil day, use absl::CivilDay
// from civil_time.h.
//
// Example:
//
//   absl::Duration a = absl::Seconds(60);
//   absl::Duration b = absl::Minutes(1);  // b == a
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Nanoseconds(T n) {
  return time_internal::FromInt64(n, std::nano{});
}
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Microseconds(T n) {
  return time_internal::FromInt64(n, std::micro{});
}
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Milliseconds(T n) {
  return time_internal::FromInt64(n, std::milli{});
}
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Seconds(T n) {
  return time_internal::FromInt64(n, std::ratio<1>{});
}
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Minutes(T n) {
  return time_internal::FromInt64(n, std::ratio<60>{});
}
template <typename T, time_internal::EnableIfIntegral<T> = 0>
constexpr Duration Hours(T n) {
  return time_internal::FromInt64(n, std::ratio<3600>{});
}

// Factory overloads for constructing `Duration` values from a floating-point
// number of the unit indicated by the factory function's name. These functions
// exist for convenience, but they are not as efficient as the integral
// factories, which should be preferred.
//
// Example:
//
//   auto a = absl::Seconds(1.5);        // OK
//   auto b = absl::Milliseconds(1500);  // BETTER
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Nanoseconds(T n) {
  return n * Nanoseconds(1);
}
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Microseconds(T n) {
  return n * Microseconds(1);
}
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Milliseconds(T n) {
  return n * Milliseconds(1);
}
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Seconds(T n) {
  if (n >= 0) {  // Note: `NaN >= 0` is false.
    if (n >= static_cast<T>((std::numeric_limits<int64_t>::max)())) {
      return InfiniteDuration();
    }
    return time_internal::MakePosDoubleDuration(n);
  } else {
    if (std::isnan(n))
      return std::signbit(n) ? -InfiniteDuration() : InfiniteDuration();
    if (n <= (std::numeric_limits<int64_t>::min)()) return -InfiniteDuration();
    return -time_internal::MakePosDoubleDuration(-n);
  }
}
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Minutes(T n) {
  return n * Minutes(1);
}
template <typename T, time_internal::EnableIfFloat<T> = 0>
Duration Hours(T n) {
  return n * Hours(1);
}

// ToInt64Nanoseconds()
// ToInt64Microseconds()
// ToInt64Milliseconds()
// ToInt64Seconds()
// ToInt64Minutes()
// ToInt64Hours()
//
// Helper functions that convert a Duration to an integral count of the
// indicated unit. These return the same results as the `IDivDuration()`
// function, though they usually do so more efficiently; see the
// documentation of `IDivDuration()` for details about overflow, etc.
//
// Example:
//
//   absl::Duration d = absl::Milliseconds(1500);
//   int64_t isec = absl::ToInt64Seconds(d);  // isec == 1
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Nanoseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Microseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Seconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Minutes(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Hours(Duration d);

// ToDoubleNanoSeconds()
// ToDoubleMicroseconds()
// ToDoubleMilliseconds()
// ToDoubleSeconds()
// ToDoubleMinutes()
// ToDoubleHours()
//
// Helper functions that convert a Duration to a floating point count of the
// indicated unit. These functions are shorthand for the `FDivDuration()`
// function above; see its documentation for details about overflow, etc.
//
// Example:
//
//   absl::Duration d = absl::Milliseconds(1500);
//   double dsec = absl::ToDoubleSeconds(d);  // dsec == 1.5
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleNanoseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMicroseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMilliseconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleSeconds(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleMinutes(Duration d);
ABSL_ATTRIBUTE_PURE_FUNCTION double ToDoubleHours(Duration d);

// FromChrono()
//
// Converts any of the pre-defined std::chrono durations to an absl::Duration.
//
// Example:
//
//   std::chrono::milliseconds ms(123);
//   absl::Duration d = absl::FromChrono(ms);
constexpr Duration FromChrono(const std::chrono::nanoseconds& d);
constexpr Duration FromChrono(const std::chrono::microseconds& d);
constexpr Duration FromChrono(const std::chrono::milliseconds& d);
constexpr Duration FromChrono(const std::chrono::seconds& d);
constexpr Duration FromChrono(const std::chrono::minutes& d);
constexpr Duration FromChrono(const std::chrono::hours& d);

// ToChronoNanoseconds()
// ToChronoMicroseconds()
// ToChronoMilliseconds()
// ToChronoSeconds()
// ToChronoMinutes()
// ToChronoHours()
//
// Converts an absl::Duration to any of the pre-defined std::chrono durations.
// If overflow would occur, the returned value will saturate at the min/max
// chrono duration value instead.
//
// Example:
//
//   absl::Duration d = absl::Microseconds(123);
//   auto x = absl::ToChronoMicroseconds(d);
//   auto y = absl::ToChronoNanoseconds(d);  // x == y
//   auto z = absl::ToChronoSeconds(absl::InfiniteDuration());
//   // z == std::chrono::seconds::max()
std::chrono::nanoseconds ToChronoNanoseconds(Duration d);
std::chrono::microseconds ToChronoMicroseconds(Duration d);
std::chrono::milliseconds ToChronoMilliseconds(Duration d);
std::chrono::seconds ToChronoSeconds(Duration d);
std::chrono::minutes ToChronoMinutes(Duration d);
std::chrono::hours ToChronoHours(Duration d);

// FormatDuration()
//
// Returns a string representing the duration in the form "72h3m0.5s".
// Returns "inf" or "-inf" for +/- `InfiniteDuration()`.
std::string FormatDuration(Duration d);

// Output stream operator.
inline std::ostream& operator<<(std::ostream& os, Duration d) {
  return os << FormatDuration(d);
}

// ParseDuration()
//
// Parses a duration string consisting of a possibly signed sequence of
// decimal numbers, each with an optional fractional part and a unit
// suffix.  The valid suffixes are "ns", "us" "ms", "s", "m", and "h".
// Simple examples include "300ms", "-1.5h", and "2h45m".  Parses "0" as
// `ZeroDuration()`. Parses "inf" and "-inf" as +/- `InfiniteDuration()`.
bool ParseDuration(absl::string_view dur_string, Duration* d);

// AbslParseFlag()
//
// Parses a command-line flag string representation `text` into a a Duration
// value. Duration flags must be specified in a format that is valid input for
// `absl::ParseDuration()`.
bool AbslParseFlag(absl::string_view text, Duration* dst, std::string* error);


// AbslUnparseFlag()
//
// Unparses a Duration value into a command-line string representation using
// the format specified by `absl::ParseDuration()`.
std::string AbslUnparseFlag(Duration d);

ABSL_DEPRECATED("Use AbslParseFlag() instead.")
bool ParseFlag(const std::string& text, Duration* dst, std::string* error);
ABSL_DEPRECATED("Use AbslUnparseFlag() instead.")
std::string UnparseFlag(Duration d);

// Time
//
// An `absl::Time` represents a specific instant in time. Arithmetic operators
// are provided for naturally expressing time calculations. Instances are
// created using `absl::Now()` and the `absl::From*()` factory functions that
// accept the gamut of other time representations. Formatting and parsing
// functions are provided for conversion to and from strings.  `absl::Time`
// should be passed by value rather than const reference.
//
// `absl::Time` assumes there are 60 seconds in a minute, which means the
// underlying time scales must be "smeared" to eliminate leap seconds.
// See https://developers.google.com/time/smear.
//
// Even though `absl::Time` supports a wide range of timestamps, exercise
// caution when using values in the distant past. `absl::Time` uses the
// Proleptic Gregorian calendar, which extends the Gregorian calendar backward
// to dates before its introduction in 1582.
// See https://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar
// for more information. Use the ICU calendar classes to convert a date in
// some other calendar (http://userguide.icu-project.org/datetime/calendar).
//
// Similarly, standardized time zones are a reasonably recent innovation, with
// the Greenwich prime meridian being established in 1884. The TZ database
// itself does not profess accurate offsets for timestamps prior to 1970. The
// breakdown of future timestamps is subject to the whim of regional
// governments.
//
// The `absl::Time` class represents an instant in time as a count of clock
// ticks of some granularity (resolution) from some starting point (epoch).
//
// `absl::Time` uses a resolution that is high enough to avoid loss in
// precision, and a range that is wide enough to avoid overflow, when
// converting between tick counts in most Google time scales (i.e., resolution
// of at least one nanosecond, and range +/-100 billion years).  Conversions
// between the time scales are performed by truncating (towards negative
// infinity) to the nearest representable point.
//
// Examples:
//
//   absl::Time t1 = ...;
//   absl::Time t2 = t1 + absl::Minutes(2);
//   absl::Duration d = t2 - t1;  // == absl::Minutes(2)
//
class Time {
 public:
  // Value semantics.

  // Returns the Unix epoch.  However, those reading your code may not know
  // or expect the Unix epoch as the default value, so make your code more
  // readable by explicitly initializing all instances before use.
  //
  // Example:
  //   absl::Time t = absl::UnixEpoch();
  //   absl::Time t = absl::Now();
  //   absl::Time t = absl::TimeFromTimeval(tv);
  //   absl::Time t = absl::InfinitePast();
  constexpr Time() = default;

  // Copyable.
  constexpr Time(const Time& t) = default;
  Time& operator=(const Time& t) = default;

  // Assignment operators.
  Time& operator+=(Duration d) {
    rep_ += d;
    return *this;
  }
  Time& operator-=(Duration d) {
    rep_ -= d;
    return *this;
  }

  // Time::Breakdown
  //
  // The calendar and wall-clock (aka "civil time") components of an
  // `absl::Time` in a certain `absl::TimeZone`. This struct is not
  // intended to represent an instant in time. So, rather than passing
  // a `Time::Breakdown` to a function, pass an `absl::Time` and an
  // `absl::TimeZone`.
  //
  // Deprecated. Use `absl::TimeZone::CivilInfo`.
  struct
      Breakdown {
    int64_t year;        // year (e.g., 2013)
    int month;           // month of year [1:12]
    int day;             // day of month [1:31]
    int hour;            // hour of day [0:23]
    int minute;          // minute of hour [0:59]
    int second;          // second of minute [0:59]
    Duration subsecond;  // [Seconds(0):Seconds(1)) if finite
    int weekday;         // 1==Mon, ..., 7=Sun
    int yearday;         // day of year [1:366]

    // Note: The following fields exist for backward compatibility
    // with older APIs.  Accessing these fields directly is a sign of
    // imprudent logic in the calling code.  Modern time-related code
    // should only access this data indirectly by way of FormatTime().
    // These fields are undefined for InfiniteFuture() and InfinitePast().
    int offset;             // seconds east of UTC
    bool is_dst;            // is offset non-standard?
    const char* zone_abbr;  // time-zone abbreviation (e.g., "PST")
  };

  // Time::In()
  //
  // Returns the breakdown of this instant in the given TimeZone.
  //
  // Deprecated. Use `absl::TimeZone::At(Time)`.
  Breakdown In(TimeZone tz) const;

  template <typename H>
  friend H AbslHashValue(H h, Time t) {
    return H::combine(std::move(h), t.rep_);
  }

 private:
  friend constexpr Time time_internal::FromUnixDuration(Duration d);
  friend constexpr Duration time_internal::ToUnixDuration(Time t);
  friend constexpr bool operator<(Time lhs, Time rhs);
  friend constexpr bool operator==(Time lhs, Time rhs);
  friend Duration operator-(Time lhs, Time rhs);
  friend constexpr Time UniversalEpoch();
  friend constexpr Time InfiniteFuture();
  friend constexpr Time InfinitePast();
  constexpr explicit Time(Duration rep) : rep_(rep) {}
  Duration rep_;
};

// Relational Operators
constexpr bool operator<(Time lhs, Time rhs) { return lhs.rep_ < rhs.rep_; }
constexpr bool operator>(Time lhs, Time rhs) { return rhs < lhs; }
constexpr bool operator>=(Time lhs, Time rhs) { return !(lhs < rhs); }
constexpr bool operator<=(Time lhs, Time rhs) { return !(rhs < lhs); }
constexpr bool operator==(Time lhs, Time rhs) { return lhs.rep_ == rhs.rep_; }
constexpr bool operator!=(Time lhs, Time rhs) { return !(lhs == rhs); }

// Additive Operators
inline Time operator+(Time lhs, Duration rhs) { return lhs += rhs; }
inline Time operator+(Duration lhs, Time rhs) { return rhs += lhs; }
inline Time operator-(Time lhs, Duration rhs) { return lhs -= rhs; }
inline Duration operator-(Time lhs, Time rhs) { return lhs.rep_ - rhs.rep_; }

// UnixEpoch()
//
// Returns the `absl::Time` representing "1970-01-01 00:00:00.0 +0000".
constexpr Time UnixEpoch() { return Time(); }

// UniversalEpoch()
//
// Returns the `absl::Time` representing "0001-01-01 00:00:00.0 +0000", the
// epoch of the ICU Universal Time Scale.
constexpr Time UniversalEpoch() {
  // 719162 is the number of days from 0001-01-01 to 1970-01-01,
  // assuming the Gregorian calendar.
  return Time(time_internal::MakeDuration(-24 * 719162 * int64_t{3600}, 0U));
}

// InfiniteFuture()
//
// Returns an `absl::Time` that is infinitely far in the future.
constexpr Time InfiniteFuture() {
  return Time(
      time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(), ~0U));
}

// InfinitePast()
//
// Returns an `absl::Time` that is infinitely far in the past.
constexpr Time InfinitePast() {
  return Time(
      time_internal::MakeDuration((std::numeric_limits<int64_t>::min)(), ~0U));
}

// FromUnixNanos()
// FromUnixMicros()
// FromUnixMillis()
// FromUnixSeconds()
// FromTimeT()
// FromUDate()
// FromUniversal()
//
// Creates an `absl::Time` from a variety of other representations.
constexpr Time FromUnixNanos(int64_t ns);
constexpr Time FromUnixMicros(int64_t us);
constexpr Time FromUnixMillis(int64_t ms);
constexpr Time FromUnixSeconds(int64_t s);
constexpr Time FromTimeT(time_t t);
Time FromUDate(double udate);
Time FromUniversal(int64_t universal);

// ToUnixNanos()
// ToUnixMicros()
// ToUnixMillis()
// ToUnixSeconds()
// ToTimeT()
// ToUDate()
// ToUniversal()
//
// Converts an `absl::Time` to a variety of other representations.  Note that
// these operations round down toward negative infinity where necessary to
// adjust to the resolution of the result type.  Beware of possible time_t
// over/underflow in ToTime{T,val,spec}() on 32-bit platforms.
int64_t ToUnixNanos(Time t);
int64_t ToUnixMicros(Time t);
int64_t ToUnixMillis(Time t);
int64_t ToUnixSeconds(Time t);
time_t ToTimeT(Time t);
double ToUDate(Time t);
int64_t ToUniversal(Time t);

// DurationFromTimespec()
// DurationFromTimeval()
// ToTimespec()
// ToTimeval()
// TimeFromTimespec()
// TimeFromTimeval()
// ToTimespec()
// ToTimeval()
//
// Some APIs use a timespec or a timeval as a Duration (e.g., nanosleep(2)
// and select(2)), while others use them as a Time (e.g. clock_gettime(2)
// and gettimeofday(2)), so conversion functions are provided for both cases.
// The "to timespec/val" direction is easily handled via overloading, but
// for "from timespec/val" the desired type is part of the function name.
Duration DurationFromTimespec(timespec ts);
Duration DurationFromTimeval(timeval tv);
timespec ToTimespec(Duration d);
timeval ToTimeval(Duration d);
Time TimeFromTimespec(timespec ts);
Time TimeFromTimeval(timeval tv);
timespec ToTimespec(Time t);
timeval ToTimeval(Time t);

// FromChrono()
//
// Converts a std::chrono::system_clock::time_point to an absl::Time.
//
// Example:
//
//   auto tp = std::chrono::system_clock::from_time_t(123);
//   absl::Time t = absl::FromChrono(tp);
//   // t == absl::FromTimeT(123)
Time FromChrono(const std::chrono::system_clock::time_point& tp);

// ToChronoTime()
//
// Converts an absl::Time to a std::chrono::system_clock::time_point. If
// overflow would occur, the returned value will saturate at the min/max time
// point value instead.
//
// Example:
//
//   absl::Time t = absl::FromTimeT(123);
//   auto tp = absl::ToChronoTime(t);
//   // tp == std::chrono::system_clock::from_time_t(123);
std::chrono::system_clock::time_point ToChronoTime(Time);

// AbslParseFlag()
//
// Parses the command-line flag string representation `text` into a Time value.
// Time flags must be specified in a format that matches absl::RFC3339_full.
//
// For example:
//
//   --start_time=2016-01-02T03:04:05.678+08:00
//
// Note: A UTC offset (or 'Z' indicating a zero-offset from UTC) is required.
//
// Additionally, if you'd like to specify a time as a count of
// seconds/milliseconds/etc from the Unix epoch, use an absl::Duration flag
// and add that duration to absl::UnixEpoch() to get an absl::Time.
bool AbslParseFlag(absl::string_view text, Time* t, std::string* error);

// AbslUnparseFlag()
//
// Unparses a Time value into a command-line string representation using
// the format specified by `absl::ParseTime()`.
std::string AbslUnparseFlag(Time t);

ABSL_DEPRECATED("Use AbslParseFlag() instead.")
bool ParseFlag(const std::string& text, Time* t, std::string* error);
ABSL_DEPRECATED("Use AbslUnparseFlag() instead.")
std::string UnparseFlag(Time t);

// TimeZone
//
// The `absl::TimeZone` is an opaque, small, value-type class representing a
// geo-political region within which particular rules are used for converting
// between absolute and civil times (see https://git.io/v59Ly). `absl::TimeZone`
// values are named using the TZ identifiers from the IANA Time Zone Database,
// such as "America/Los_Angeles" or "Australia/Sydney". `absl::TimeZone` values
// are created from factory functions such as `absl::LoadTimeZone()`. Note:
// strings like "PST" and "EDT" are not valid TZ identifiers. Prefer to pass by
// value rather than const reference.
//
// For more on the fundamental concepts of time zones, absolute times, and civil
// times, see https://github.com/google/cctz#fundamental-concepts
//
// Examples:
//
//   absl::TimeZone utc = absl::UTCTimeZone();
//   absl::TimeZone pst = absl::FixedTimeZone(-8 * 60 * 60);
//   absl::TimeZone loc = absl::LocalTimeZone();
//   absl::TimeZone lax;
//   if (!absl::LoadTimeZone("America/Los_Angeles", &lax)) {
//     // handle error case
//   }
//
// See also:
// - https://github.com/google/cctz
// - https://www.iana.org/time-zones
// - https://en.wikipedia.org/wiki/Zoneinfo
class TimeZone {
 public:
  explicit TimeZone(time_internal::cctz::time_zone tz) : cz_(tz) {}
  TimeZone() = default;  // UTC, but prefer UTCTimeZone() to be explicit.

  // Copyable.
  TimeZone(const TimeZone&) = default;
  TimeZone& operator=(const TimeZone&) = default;

  explicit operator time_internal::cctz::time_zone() const { return cz_; }

  std::string name() const { return cz_.name(); }

  // TimeZone::CivilInfo
  //
  // Information about the civil time corresponding to an absolute time.
  // This struct is not intended to represent an instant in time. So, rather
  // than passing a `TimeZone::CivilInfo` to a function, pass an `absl::Time`
  // and an `absl::TimeZone`.
  struct CivilInfo {
    CivilSecond cs;
    Duration subsecond;

    // Note: The following fields exist for backward compatibility
    // with older APIs.  Accessing these fields directly is a sign of
    // imprudent logic in the calling code.  Modern time-related code
    // should only access this data indirectly by way of FormatTime().
    // These fields are undefined for InfiniteFuture() and InfinitePast().
    int offset;             // seconds east of UTC
    bool is_dst;            // is offset non-standard?
    const char* zone_abbr;  // time-zone abbreviation (e.g., "PST")
  };

  // TimeZone::At(Time)
  //
  // Returns the civil time for this TimeZone at a certain `absl::Time`.
  // If the input time is infinite, the output civil second will be set to
  // CivilSecond::max() or min(), and the subsecond will be infinite.
  //
  // Example:
  //
  //   const auto epoch = lax.At(absl::UnixEpoch());
  //   // epoch.cs == 1969-12-31 16:00:00
  //   // epoch.subsecond == absl::ZeroDuration()
  //   // epoch.offset == -28800
  //   // epoch.is_dst == false
  //   // epoch.abbr == "PST"
  CivilInfo At(Time t) const;

  // TimeZone::TimeInfo
  //
  // Information about the absolute times corresponding to a civil time.
  // (Subseconds must be handled separately.)
  //
  // It is possible for a caller to pass a civil-time value that does
  // not represent an actual or unique instant in time (due to a shift
  // in UTC offset in the TimeZone, which results in a discontinuity in
  // the civil-time components). For example, a daylight-saving-time
  // transition skips or repeats civil times---in the United States,
  // March 13, 2011 02:15 never occurred, while November 6, 2011 01:15
  // occurred twice---so requests for such times are not well-defined.
  // To account for these possibilities, `absl::TimeZone::TimeInfo` is
  // richer than just a single `absl::Time`.
  struct TimeInfo {
    enum CivilKind {
      UNIQUE,    // the civil time was singular (pre == trans == post)
      SKIPPED,   // the civil time did not exist (pre >= trans > post)
      REPEATED,  // the civil time was ambiguous (pre < trans <= post)
    } kind;
    Time pre;    // time calculated using the pre-transition offset
    Time trans;  // when the civil-time discontinuity occurred
    Time post;   // time calculated using the post-transition offset
  };

  // TimeZone::At(CivilSecond)
  //
  // Returns an `absl::TimeInfo` containing the absolute time(s) for this
  // TimeZone at an `absl::CivilSecond`. When the civil time is skipped or
  // repeated, returns times calculated using the pre-transition and post-
  // transition UTC offsets, plus the transition time itself.
  //
  // Examples:
  //
  //   // A unique civil time
  //   const auto jan01 = lax.At(absl::CivilSecond(2011, 1, 1, 0, 0, 0));
  //   // jan01.kind == TimeZone::TimeInfo::UNIQUE
  //   // jan01.pre    is 2011-01-01 00:00:00 -0800
  //   // jan01.trans  is 2011-01-01 00:00:00 -0800
  //   // jan01.post   is 2011-01-01 00:00:00 -0800
  //
  //   // A Spring DST transition, when there is a gap in civil time
  //   const auto mar13 = lax.At(absl::CivilSecond(2011, 3, 13, 2, 15, 0));
  //   // mar13.kind == TimeZone::TimeInfo::SKIPPED
  //   // mar13.pre   is 2011-03-13 03:15:00 -0700
  //   // mar13.trans is 2011-03-13 03:00:00 -0700
  //   // mar13.post  is 2011-03-13 01:15:00 -0800
  //
  //   // A Fall DST transition, when civil times are repeated
  //   const auto nov06 = lax.At(absl::CivilSecond(2011, 11, 6, 1, 15, 0));
  //   // nov06.kind == TimeZone::TimeInfo::REPEATED
  //   // nov06.pre   is 2011-11-06 01:15:00 -0700
  //   // nov06.trans is 2011-11-06 01:00:00 -0800
  //   // nov06.post  is 2011-11-06 01:15:00 -0800
  TimeInfo At(CivilSecond ct) const;

  // TimeZone::NextTransition()
  // TimeZone::PrevTransition()
  //
  // Finds the time of the next/previous offset change in this time zone.
  //
  // By definition, `NextTransition(t, &trans)` returns false when `t` is
  // `InfiniteFuture()`, and `PrevTransition(t, &trans)` returns false
  // when `t` is `InfinitePast()`. If the zone has no transitions, the
  // result will also be false no matter what the argument.
  //
  // Otherwise, when `t` is `InfinitePast()`, `NextTransition(t, &trans)`
  // returns true and sets `trans` to the first recorded transition. Chains
  // of calls to `NextTransition()/PrevTransition()` will eventually return
  // false, but it is unspecified exactly when `NextTransition(t, &trans)`
  // jumps to false, or what time is set by `PrevTransition(t, &trans)` for
  // a very distant `t`.
  //
  // Note: Enumeration of time-zone transitions is for informational purposes
  // only. Modern time-related code should not care about when offset changes
  // occur.
  //
  // Example:
  //   absl::TimeZone nyc;
  //   if (!absl::LoadTimeZone("America/New_York", &nyc)) { ... }
  //   const auto now = absl::Now();
  //   auto t = absl::InfinitePast();
  //   absl::TimeZone::CivilTransition trans;
  //   while (t <= now && nyc.NextTransition(t, &trans)) {
  //     // transition: trans.from -> trans.to
  //     t = nyc.At(trans.to).trans;
  //   }
  struct CivilTransition {
    CivilSecond from;  // the civil time we jump from
    CivilSecond to;    // the civil time we jump to
  };
  bool NextTransition(Time t, CivilTransition* trans) const;
  bool PrevTransition(Time t, CivilTransition* trans) const;

  template <typename H>
  friend H AbslHashValue(H h, TimeZone tz) {
    return H::combine(std::move(h), tz.cz_);
  }

 private:
  friend bool operator==(TimeZone a, TimeZone b) { return a.cz_ == b.cz_; }
  friend bool operator!=(TimeZone a, TimeZone b) { return a.cz_ != b.cz_; }
  friend std::ostream& operator<<(std::ostream& os, TimeZone tz) {
    return os << tz.name();
  }

  time_internal::cctz::time_zone cz_;
};

// LoadTimeZone()
//
// Loads the named zone. May perform I/O on the initial load of the named
// zone. If the name is invalid, or some other kind of error occurs, returns
// `false` and `*tz` is set to the UTC time zone.
inline bool LoadTimeZone(absl::string_view name, TimeZone* tz) {
  if (name == "localtime") {
    *tz = TimeZone(time_internal::cctz::local_time_zone());
    return true;
  }
  time_internal::cctz::time_zone cz;
  const bool b = time_internal::cctz::load_time_zone(std::string(name), &cz);
  *tz = TimeZone(cz);
  return b;
}

// FixedTimeZone()
//
// Returns a TimeZone that is a fixed offset (seconds east) from UTC.
// Note: If the absolute value of the offset is greater than 24 hours
// you'll get UTC (i.e., no offset) instead.
inline TimeZone FixedTimeZone(int seconds) {
  return TimeZone(
      time_internal::cctz::fixed_time_zone(std::chrono::seconds(seconds)));
}

// UTCTimeZone()
//
// Convenience method returning the UTC time zone.
inline TimeZone UTCTimeZone() {
  return TimeZone(time_internal::cctz::utc_time_zone());
}

// LocalTimeZone()
//
// Convenience method returning the local time zone, or UTC if there is
// no configured local zone.  Warning: Be wary of using LocalTimeZone(),
// and particularly so in a server process, as the zone configured for the
// local machine should be irrelevant.  Prefer an explicit zone name.
inline TimeZone LocalTimeZone() {
  return TimeZone(time_internal::cctz::local_time_zone());
}

// ToCivilSecond()
// ToCivilMinute()
// ToCivilHour()
// ToCivilDay()
// ToCivilMonth()
// ToCivilYear()
//
// Helpers for TimeZone::At(Time) to return particularly aligned civil times.
//
// Example:
//
//   absl::Time t = ...;
//   absl::TimeZone tz = ...;
//   const auto cd = absl::ToCivilDay(t, tz);
inline CivilSecond ToCivilSecond(Time t, TimeZone tz) {
  return tz.At(t).cs;  // already a CivilSecond
}
inline CivilMinute ToCivilMinute(Time t, TimeZone tz) {
  return CivilMinute(tz.At(t).cs);
}
inline CivilHour ToCivilHour(Time t, TimeZone tz) {
  return CivilHour(tz.At(t).cs);
}
inline CivilDay ToCivilDay(Time t, TimeZone tz) {
  return CivilDay(tz.At(t).cs);
}
inline CivilMonth ToCivilMonth(Time t, TimeZone tz) {
  return CivilMonth(tz.At(t).cs);
}
inline CivilYear ToCivilYear(Time t, TimeZone tz) {
  return CivilYear(tz.At(t).cs);
}

// FromCivil()
//
// Helper for TimeZone::At(CivilSecond) that provides "order-preserving
// semantics." If the civil time maps to a unique time, that time is
// returned. If the civil time is repeated in the given time zone, the
// time using the pre-transition offset is returned. Otherwise, the
// civil time is skipped in the given time zone, and the transition time
// is returned. This means that for any two civil times, ct1 and ct2,
// (ct1 < ct2) => (FromCivil(ct1) <= FromCivil(ct2)), the equal case
// being when two non-existent civil times map to the same transition time.
//
// Note: Accepts civil times of any alignment.
inline Time FromCivil(CivilSecond ct, TimeZone tz) {
  const auto ti = tz.At(ct);
  if (ti.kind == TimeZone::TimeInfo::SKIPPED) return ti.trans;
  return ti.pre;
}

// TimeConversion
//
// An `absl::TimeConversion` represents the conversion of year, month, day,
// hour, minute, and second values (i.e., a civil time), in a particular
// `absl::TimeZone`, to a time instant (an absolute time), as returned by
// `absl::ConvertDateTime()`. Legacy version of `absl::TimeZone::TimeInfo`.
//
// Deprecated. Use `absl::TimeZone::TimeInfo`.
struct
    TimeConversion {
  Time pre;    // time calculated using the pre-transition offset
  Time trans;  // when the civil-time discontinuity occurred
  Time post;   // time calculated using the post-transition offset

  enum Kind {
    UNIQUE,    // the civil time was singular (pre == trans == post)
    SKIPPED,   // the civil time did not exist
    REPEATED,  // the civil time was ambiguous
  };
  Kind kind;

  bool normalized;  // input values were outside their valid ranges
};

// ConvertDateTime()
//
// Legacy version of `absl::TimeZone::At(absl::CivilSecond)` that takes
// the civil time as six, separate values (YMDHMS).
//
// The input month, day, hour, minute, and second values can be outside
// of their valid ranges, in which case they will be "normalized" during
// the conversion.
//
// Example:
//
//   // "October 32" normalizes to "November 1".
//   absl::TimeConversion tc =
//       absl::ConvertDateTime(2013, 10, 32, 8, 30, 0, lax);
//   // tc.kind == TimeConversion::UNIQUE && tc.normalized == true
//   // absl::ToCivilDay(tc.pre, tz).month() == 11
//   // absl::ToCivilDay(tc.pre, tz).day() == 1
//
// Deprecated. Use `absl::TimeZone::At(CivilSecond)`.
TimeConversion ConvertDateTime(int64_t year, int mon, int day, int hour,
                               int min, int sec, TimeZone tz);

// FromDateTime()
//
// A convenience wrapper for `absl::ConvertDateTime()` that simply returns
// the "pre" `absl::Time`.  That is, the unique result, or the instant that
// is correct using the pre-transition offset (as if the transition never
// happened).
//
// Example:
//
//   absl::Time t = absl::FromDateTime(2017, 9, 26, 9, 30, 0, lax);
//   // t = 2017-09-26 09:30:00 -0700
//
// Deprecated. Use `absl::FromCivil(CivilSecond, TimeZone)`. Note that the
// behavior of `FromCivil()` differs from `FromDateTime()` for skipped civil
// times. If you care about that see `absl::TimeZone::At(absl::CivilSecond)`.
inline Time FromDateTime(int64_t year, int mon, int day, int hour,
                         int min, int sec, TimeZone tz) {
  return ConvertDateTime(year, mon, day, hour, min, sec, tz).pre;
}

// FromTM()
//
// Converts the `tm_year`, `tm_mon`, `tm_mday`, `tm_hour`, `tm_min`, and
// `tm_sec` fields to an `absl::Time` using the given time zone. See ctime(3)
// for a description of the expected values of the tm fields. If the civil time
// is unique (see `absl::TimeZone::At(absl::CivilSecond)` above), the matching
// time instant is returned.  Otherwise, the `tm_isdst` field is consulted to
// choose between the possible results.  For a repeated civil time, `tm_isdst !=
// 0` returns the matching DST instant, while `tm_isdst == 0` returns the
// matching non-DST instant.  For a skipped civil time there is no matching
// instant, so `tm_isdst != 0` returns the DST instant, and `tm_isdst == 0`
// returns the non-DST instant, that would have matched if the transition never
// happened.
Time FromTM(const struct tm& tm, TimeZone tz);

// ToTM()
//
// Converts the given `absl::Time` to a struct tm using the given time zone.
// See ctime(3) for a description of the values of the tm fields.
struct tm ToTM(Time t, TimeZone tz);

// RFC3339_full
// RFC3339_sec
//
// FormatTime()/ParseTime() format specifiers for RFC3339 date/time strings,
// with trailing zeros trimmed or with fractional seconds omitted altogether.
//
// Note that RFC3339_sec[] matches an ISO 8601 extended format for date and
// time with UTC offset.  Also note the use of "%Y": RFC3339 mandates that
// years have exactly four digits, but we allow them to take their natural
// width.
ABSL_DLL extern const char RFC3339_full[];  // %Y-%m-%d%ET%H:%M:%E*S%Ez
ABSL_DLL extern const char RFC3339_sec[];   // %Y-%m-%d%ET%H:%M:%S%Ez

// RFC1123_full
// RFC1123_no_wday
//
// FormatTime()/ParseTime() format specifiers for RFC1123 date/time strings.
ABSL_DLL extern const char RFC1123_full[];     // %a, %d %b %E4Y %H:%M:%S %z
ABSL_DLL extern const char RFC1123_no_wday[];  // %d %b %E4Y %H:%M:%S %z

// FormatTime()
//
// Formats the given `absl::Time` in the `absl::TimeZone` according to the
// provided format string. Uses strftime()-like formatting options, with
// the following extensions:
//
//   - %Ez  - RFC3339-compatible numeric UTC offset (+hh:mm or -hh:mm)
//   - %E*z - Full-resolution numeric UTC offset (+hh:mm:ss or -hh:mm:ss)
//   - %E#S - Seconds with # digits of fractional precision
//   - %E*S - Seconds with full fractional precision (a literal '*')
//   - %E#f - Fractional seconds with # digits of precision
//   - %E*f - Fractional seconds with full precision (a literal '*')
//   - %E4Y - Four-character years (-999 ... -001, 0000, 0001 ... 9999)
//   - %ET  - The RFC3339 "date-time" separator "T"
//
// Note that %E0S behaves like %S, and %E0f produces no characters.  In
// contrast %E*f always produces at least one digit, which may be '0'.
//
// Note that %Y produces as many characters as it takes to fully render the
// year.  A year outside of [-999:9999] when formatted with %E4Y will produce
// more than four characters, just like %Y.
//
// We recommend that format strings include the UTC offset (%z, %Ez, or %E*z)
// so that the result uniquely identifies a time instant.
//
// Example:
//
//   absl::CivilSecond cs(2013, 1, 2, 3, 4, 5);
//   absl::Time t = absl::FromCivil(cs, lax);
//   std::string f = absl::FormatTime("%H:%M:%S", t, lax);  // "03:04:05"
//   f = absl::FormatTime("%H:%M:%E3S", t, lax);  // "03:04:05.000"
//
// Note: If the given `absl::Time` is `absl::InfiniteFuture()`, the returned
// string will be exactly "infinite-future". If the given `absl::Time` is
// `absl::InfinitePast()`, the returned string will be exactly "infinite-past".
// In both cases the given format string and `absl::TimeZone` are ignored.
//
std::string FormatTime(absl::string_view format, Time t, TimeZone tz);

// Convenience functions that format the given time using the RFC3339_full
// format.  The first overload uses the provided TimeZone, while the second
// uses LocalTimeZone().
std::string FormatTime(Time t, TimeZone tz);
std::string FormatTime(Time t);

// Output stream operator.
inline std::ostream& operator<<(std::ostream& os, Time t) {
  return os << FormatTime(t);
}

// ParseTime()
//
// Parses an input string according to the provided format string and
// returns the corresponding `absl::Time`. Uses strftime()-like formatting
// options, with the same extensions as FormatTime(), but with the
// exceptions that %E#S is interpreted as %E*S, and %E#f as %E*f.  %Ez
// and %E*z also accept the same inputs, which (along with %z) includes
// 'z' and 'Z' as synonyms for +00:00.  %ET accepts either 'T' or 't'.
//
// %Y consumes as many numeric characters as it can, so the matching data
// should always be terminated with a non-numeric.  %E4Y always consumes
// exactly four characters, including any sign.
//
// Unspecified fields are taken from the default date and time of ...
//
//   "1970-01-01 00:00:00.0 +0000"
//
// For example, parsing a string of "15:45" (%H:%M) will return an absl::Time
// that represents "1970-01-01 15:45:00.0 +0000".
//
// Note that since ParseTime() returns time instants, it makes the most sense
// to parse fully-specified date/time strings that include a UTC offset (%z,
// %Ez, or %E*z).
//
// Note also that `absl::ParseTime()` only heeds the fields year, month, day,
// hour, minute, (fractional) second, and UTC offset.  Other fields, like
// weekday (%a or %A), while parsed for syntactic validity, are ignored
// in the conversion.
//
// Date and time fields that are out-of-range will be treated as errors
// rather than normalizing them like `absl::CivilSecond` does.  For example,
// it is an error to parse the date "Oct 32, 2013" because 32 is out of range.
//
// A leap second of ":60" is normalized to ":00" of the following minute
// with fractional seconds discarded.  The following table shows how the
// given seconds and subseconds will be parsed:
//
//   "59.x" -> 59.x  // exact
//   "60.x" -> 00.0  // normalized
//   "00.x" -> 00.x  // exact
//
// Errors are indicated by returning false and assigning an error message
// to the "err" out param if it is non-null.
//
// Note: If the input string is exactly "infinite-future", the returned
// `absl::Time` will be `absl::InfiniteFuture()` and `true` will be returned.
// If the input string is "infinite-past", the returned `absl::Time` will be
// `absl::InfinitePast()` and `true` will be returned.
//
bool ParseTime(absl::string_view format, absl::string_view input, Time* time,
               std::string* err);

// Like ParseTime() above, but if the format string does not contain a UTC
// offset specification (%z/%Ez/%E*z) then the input is interpreted in the
// given TimeZone.  This means that the input, by itself, does not identify a
// unique instant.  Being time-zone dependent, it also admits the possibility
// of ambiguity or non-existence, in which case the "pre" time (as defined
// by TimeZone::TimeInfo) is returned.  For these reasons we recommend that
// all date/time strings include a UTC offset so they're context independent.
bool ParseTime(absl::string_view format, absl::string_view input, TimeZone tz,
               Time* time, std::string* err);

// ============================================================================
// Implementation Details Follow
// ============================================================================

namespace time_internal {

// Creates a Duration with a given representation.
// REQUIRES: hi,lo is a valid representation of a Duration as specified
// in time/duration.cc.
constexpr Duration MakeDuration(int64_t hi, uint32_t lo = 0) {
  return Duration(hi, lo);
}

constexpr Duration MakeDuration(int64_t hi, int64_t lo) {
  return MakeDuration(hi, static_cast<uint32_t>(lo));
}

// Make a Duration value from a floating-point number, as long as that number
// is in the range [ 0 .. numeric_limits<int64_t>::max ), that is, as long as
// it's positive and can be converted to int64_t without risk of UB.
inline Duration MakePosDoubleDuration(double n) {
  const int64_t int_secs = static_cast<int64_t>(n);
  const uint32_t ticks = static_cast<uint32_t>(
      std::round((n - static_cast<double>(int_secs)) * kTicksPerSecond));
  return ticks < kTicksPerSecond
             ? MakeDuration(int_secs, ticks)
             : MakeDuration(int_secs + 1, ticks - kTicksPerSecond);
}

// Creates a normalized Duration from an almost-normalized (sec,ticks)
// pair. sec may be positive or negative.  ticks must be in the range
// -kTicksPerSecond < *ticks < kTicksPerSecond.  If ticks is negative it
// will be normalized to a positive value in the resulting Duration.
constexpr Duration MakeNormalizedDuration(int64_t sec, int64_t ticks) {
  return (ticks < 0) ? MakeDuration(sec - 1, ticks + kTicksPerSecond)
                     : MakeDuration(sec, ticks);
}

// Provide access to the Duration representation.
constexpr int64_t GetRepHi(Duration d) { return d.rep_hi_; }
constexpr uint32_t GetRepLo(Duration d) { return d.rep_lo_; }

// Returns true iff d is positive or negative infinity.
constexpr bool IsInfiniteDuration(Duration d) { return GetRepLo(d) == ~0U; }

// Returns an infinite Duration with the opposite sign.
// REQUIRES: IsInfiniteDuration(d)
constexpr Duration OppositeInfinity(Duration d) {
  return GetRepHi(d) < 0
             ? MakeDuration((std::numeric_limits<int64_t>::max)(), ~0U)
             : MakeDuration((std::numeric_limits<int64_t>::min)(), ~0U);
}

// Returns (-n)-1 (equivalently -(n+1)) without avoidable overflow.
constexpr int64_t NegateAndSubtractOne(int64_t n) {
  // Note: Good compilers will optimize this expression to ~n when using
  // a two's-complement representation (which is required for int64_t).
  return (n < 0) ? -(n + 1) : (-n) - 1;
}

// Map between a Time and a Duration since the Unix epoch.  Note that these
// functions depend on the above mentioned choice of the Unix epoch for the
// Time representation (and both need to be Time friends).  Without this
// knowledge, we would need to add-in/subtract-out UnixEpoch() respectively.
constexpr Time FromUnixDuration(Duration d) { return Time(d); }
constexpr Duration ToUnixDuration(Time t) { return t.rep_; }

template <std::intmax_t N>
constexpr Duration FromInt64(int64_t v, std::ratio<1, N>) {
  static_assert(0 < N && N <= 1000 * 1000 * 1000, "Unsupported ratio");
  // Subsecond ratios cannot overflow.
  return MakeNormalizedDuration(
      v / N, v % N * kTicksPerNanosecond * 1000 * 1000 * 1000 / N);
}
constexpr Duration FromInt64(int64_t v, std::ratio<60>) {
  return (v <= (std::numeric_limits<int64_t>::max)() / 60 &&
          v >= (std::numeric_limits<int64_t>::min)() / 60)
             ? MakeDuration(v * 60)
             : v > 0 ? InfiniteDuration() : -InfiniteDuration();
}
constexpr Duration FromInt64(int64_t v, std::ratio<3600>) {
  return (v <= (std::numeric_limits<int64_t>::max)() / 3600 &&
          v >= (std::numeric_limits<int64_t>::min)() / 3600)
             ? MakeDuration(v * 3600)
             : v > 0 ? InfiniteDuration() : -InfiniteDuration();
}

// IsValidRep64<T>(0) is true if the expression `int64_t{std::declval<T>()}` is
// valid. That is, if a T can be assigned to an int64_t without narrowing.
template <typename T>
constexpr auto IsValidRep64(int) -> decltype(int64_t{std::declval<T>()} == 0) {
  return true;
}
template <typename T>
constexpr auto IsValidRep64(char) -> bool {
  return false;
}

// Converts a std::chrono::duration to an absl::Duration.
template <typename Rep, typename Period>
constexpr Duration FromChrono(const std::chrono::duration<Rep, Period>& d) {
  static_assert(IsValidRep64<Rep>(0), "duration::rep is invalid");
  return FromInt64(int64_t{d.count()}, Period{});
}

template <typename Ratio>
int64_t ToInt64(Duration d, Ratio) {
  // Note: This may be used on MSVC, which may have a system_clock period of
  // std::ratio<1, 10 * 1000 * 1000>
  return ToInt64Seconds(d * Ratio::den / Ratio::num);
}
// Fastpath implementations for the 6 common duration units.
inline int64_t ToInt64(Duration d, std::nano) {
  return ToInt64Nanoseconds(d);
}
inline int64_t ToInt64(Duration d, std::micro) {
  return ToInt64Microseconds(d);
}
inline int64_t ToInt64(Duration d, std::milli) {
  return ToInt64Milliseconds(d);
}
inline int64_t ToInt64(Duration d, std::ratio<1>) {
  return ToInt64Seconds(d);
}
inline int64_t ToInt64(Duration d, std::ratio<60>) {
  return ToInt64Minutes(d);
}
inline int64_t ToInt64(Duration d, std::ratio<3600>) {
  return ToInt64Hours(d);
}

// Converts an absl::Duration to a chrono duration of type T.
template <typename T>
T ToChronoDuration(Duration d) {
  using Rep = typename T::rep;
  using Period = typename T::period;
  static_assert(IsValidRep64<Rep>(0), "duration::rep is invalid");
  if (time_internal::IsInfiniteDuration(d))
    return d < ZeroDuration() ? (T::min)() : (T::max)();
  const auto v = ToInt64(d, Period{});
  if (v > (std::numeric_limits<Rep>::max)()) return (T::max)();
  if (v < (std::numeric_limits<Rep>::min)()) return (T::min)();
  return T{v};
}

}  // namespace time_internal

constexpr bool operator<(Duration lhs, Duration rhs) {
  return time_internal::GetRepHi(lhs) != time_internal::GetRepHi(rhs)
             ? time_internal::GetRepHi(lhs) < time_internal::GetRepHi(rhs)
         : time_internal::GetRepHi(lhs) == (std::numeric_limits<int64_t>::min)()
             ? time_internal::GetRepLo(lhs) + 1 <
                   time_internal::GetRepLo(rhs) + 1
             : time_internal::GetRepLo(lhs) < time_internal::GetRepLo(rhs);
}

constexpr bool operator==(Duration lhs, Duration rhs) {
  return time_internal::GetRepHi(lhs) == time_internal::GetRepHi(rhs) &&
         time_internal::GetRepLo(lhs) == time_internal::GetRepLo(rhs);
}

constexpr Duration operator-(Duration d) {
  // This is a little interesting because of the special cases.
  //
  // If rep_lo_ is zero, we have it easy; it's safe to negate rep_hi_, we're
  // dealing with an integral number of seconds, and the only special case is
  // the maximum negative finite duration, which can't be negated.
  //
  // Infinities stay infinite, and just change direction.
  //
  // Finally we're in the case where rep_lo_ is non-zero, and we can borrow
  // a second's worth of ticks and avoid overflow (as negating int64_t-min + 1
  // is safe).
  return time_internal::GetRepLo(d) == 0
             ? time_internal::GetRepHi(d) ==
                       (std::numeric_limits<int64_t>::min)()
                   ? InfiniteDuration()
                   : time_internal::MakeDuration(-time_internal::GetRepHi(d))
             : time_internal::IsInfiniteDuration(d)
                   ? time_internal::OppositeInfinity(d)
                   : time_internal::MakeDuration(
                         time_internal::NegateAndSubtractOne(
                             time_internal::GetRepHi(d)),
                         time_internal::kTicksPerSecond -
                             time_internal::GetRepLo(d));
}

constexpr Duration InfiniteDuration() {
  return time_internal::MakeDuration((std::numeric_limits<int64_t>::max)(),
                                     ~0U);
}

constexpr Duration FromChrono(const std::chrono::nanoseconds& d) {
  return time_internal::FromChrono(d);
}
constexpr Duration FromChrono(const std::chrono::microseconds& d) {
  return time_internal::FromChrono(d);
}
constexpr Duration FromChrono(const std::chrono::milliseconds& d) {
  return time_internal::FromChrono(d);
}
constexpr Duration FromChrono(const std::chrono::seconds& d) {
  return time_internal::FromChrono(d);
}
constexpr Duration FromChrono(const std::chrono::minutes& d) {
  return time_internal::FromChrono(d);
}
constexpr Duration FromChrono(const std::chrono::hours& d) {
  return time_internal::FromChrono(d);
}

constexpr Time FromUnixNanos(int64_t ns) {
  return time_internal::FromUnixDuration(Nanoseconds(ns));
}

constexpr Time FromUnixMicros(int64_t us) {
  return time_internal::FromUnixDuration(Microseconds(us));
}

constexpr Time FromUnixMillis(int64_t ms) {
  return time_internal::FromUnixDuration(Milliseconds(ms));
}

constexpr Time FromUnixSeconds(int64_t s) {
  return time_internal::FromUnixDuration(Seconds(s));
}

constexpr Time FromTimeT(time_t t) {
  return time_internal::FromUnixDuration(Seconds(t));
}

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_TIME_TIME_H_