Source file src/time/time.go
1 // Copyright 2009 The Go Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style 3 // license that can be found in the LICENSE file. 4 5 // Package time provides functionality for measuring and displaying time. 6 // 7 // The calendrical calculations always assume a Gregorian calendar, with 8 // no leap seconds. 9 // 10 // Monotonic Clocks 11 // 12 // Operating systems provide both a “wall clock,” which is subject to 13 // changes for clock synchronization, and a “monotonic clock,” which is 14 // not. The general rule is that the wall clock is for telling time and 15 // the monotonic clock is for measuring time. Rather than split the API, 16 // in this package the Time returned by time.Now contains both a wall 17 // clock reading and a monotonic clock reading; later time-telling 18 // operations use the wall clock reading, but later time-measuring 19 // operations, specifically comparisons and subtractions, use the 20 // monotonic clock reading. 21 // 22 // For example, this code always computes a positive elapsed time of 23 // approximately 20 milliseconds, even if the wall clock is changed during 24 // the operation being timed: 25 // 26 // start := time.Now() 27 // ... operation that takes 20 milliseconds ... 28 // t := time.Now() 29 // elapsed := t.Sub(start) 30 // 31 // Other idioms, such as time.Since(start), time.Until(deadline), and 32 // time.Now().Before(deadline), are similarly robust against wall clock 33 // resets. 34 // 35 // The rest of this section gives the precise details of how operations 36 // use monotonic clocks, but understanding those details is not required 37 // to use this package. 38 // 39 // The Time returned by time.Now contains a monotonic clock reading. 40 // If Time t has a monotonic clock reading, t.Add adds the same duration to 41 // both the wall clock and monotonic clock readings to compute the result. 42 // Because t.AddDate(y, m, d), t.Round(d), and t.Truncate(d) are wall time 43 // computations, they always strip any monotonic clock reading from their results. 44 // Because t.In, t.Local, and t.UTC are used for their effect on the interpretation 45 // of the wall time, they also strip any monotonic clock reading from their results. 46 // The canonical way to strip a monotonic clock reading is to use t = t.Round(0). 47 // 48 // If Times t and u both contain monotonic clock readings, the operations 49 // t.After(u), t.Before(u), t.Equal(u), and t.Sub(u) are carried out 50 // using the monotonic clock readings alone, ignoring the wall clock 51 // readings. If either t or u contains no monotonic clock reading, these 52 // operations fall back to using the wall clock readings. 53 // 54 // On some systems the monotonic clock will stop if the computer goes to sleep. 55 // On such a system, t.Sub(u) may not accurately reflect the actual 56 // time that passed between t and u. 57 // 58 // Because the monotonic clock reading has no meaning outside 59 // the current process, the serialized forms generated by t.GobEncode, 60 // t.MarshalBinary, t.MarshalJSON, and t.MarshalText omit the monotonic 61 // clock reading, and t.Format provides no format for it. Similarly, the 62 // constructors time.Date, time.Parse, time.ParseInLocation, and time.Unix, 63 // as well as the unmarshalers t.GobDecode, t.UnmarshalBinary. 64 // t.UnmarshalJSON, and t.UnmarshalText always create times with 65 // no monotonic clock reading. 66 // 67 // Note that the Go == operator compares not just the time instant but 68 // also the Location and the monotonic clock reading. See the 69 // documentation for the Time type for a discussion of equality 70 // testing for Time values. 71 // 72 // For debugging, the result of t.String does include the monotonic 73 // clock reading if present. If t != u because of different monotonic clock readings, 74 // that difference will be visible when printing t.String() and u.String(). 75 // 76 package time 77 78 import ( 79 "errors" 80 _ "unsafe" // for go:linkname 81 ) 82 83 // A Time represents an instant in time with nanosecond precision. 84 // 85 // Programs using times should typically store and pass them as values, 86 // not pointers. That is, time variables and struct fields should be of 87 // type time.Time, not *time.Time. 88 // 89 // A Time value can be used by multiple goroutines simultaneously except 90 // that the methods GobDecode, UnmarshalBinary, UnmarshalJSON and 91 // UnmarshalText are not concurrency-safe. 92 // 93 // Time instants can be compared using the Before, After, and Equal methods. 94 // The Sub method subtracts two instants, producing a Duration. 95 // The Add method adds a Time and a Duration, producing a Time. 96 // 97 // The zero value of type Time is January 1, year 1, 00:00:00.000000000 UTC. 98 // As this time is unlikely to come up in practice, the IsZero method gives 99 // a simple way of detecting a time that has not been initialized explicitly. 100 // 101 // Each Time has associated with it a Location, consulted when computing the 102 // presentation form of the time, such as in the Format, Hour, and Year methods. 103 // The methods Local, UTC, and In return a Time with a specific location. 104 // Changing the location in this way changes only the presentation; it does not 105 // change the instant in time being denoted and therefore does not affect the 106 // computations described in earlier paragraphs. 107 // 108 // Representations of a Time value saved by the GobEncode, MarshalBinary, 109 // MarshalJSON, and MarshalText methods store the Time.Location's offset, but not 110 // the location name. They therefore lose information about Daylight Saving Time. 111 // 112 // In addition to the required “wall clock” reading, a Time may contain an optional 113 // reading of the current process's monotonic clock, to provide additional precision 114 // for comparison or subtraction. 115 // See the “Monotonic Clocks” section in the package documentation for details. 116 // 117 // Note that the Go == operator compares not just the time instant but also the 118 // Location and the monotonic clock reading. Therefore, Time values should not 119 // be used as map or database keys without first guaranteeing that the 120 // identical Location has been set for all values, which can be achieved 121 // through use of the UTC or Local method, and that the monotonic clock reading 122 // has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u) 123 // to t == u, since t.Equal uses the most accurate comparison available and 124 // correctly handles the case when only one of its arguments has a monotonic 125 // clock reading. 126 // 127 type Time struct { 128 // wall and ext encode the wall time seconds, wall time nanoseconds, 129 // and optional monotonic clock reading in nanoseconds. 130 // 131 // From high to low bit position, wall encodes a 1-bit flag (hasMonotonic), 132 // a 33-bit seconds field, and a 30-bit wall time nanoseconds field. 133 // The nanoseconds field is in the range [0, 999999999]. 134 // If the hasMonotonic bit is 0, then the 33-bit field must be zero 135 // and the full signed 64-bit wall seconds since Jan 1 year 1 is stored in ext. 136 // If the hasMonotonic bit is 1, then the 33-bit field holds a 33-bit 137 // unsigned wall seconds since Jan 1 year 1885, and ext holds a 138 // signed 64-bit monotonic clock reading, nanoseconds since process start. 139 wall uint64 140 ext int64 141 142 // loc specifies the Location that should be used to 143 // determine the minute, hour, month, day, and year 144 // that correspond to this Time. 145 // The nil location means UTC. 146 // All UTC times are represented with loc==nil, never loc==&utcLoc. 147 loc *Location 148 } 149 150 const ( 151 hasMonotonic = 1 << 63 152 maxWall = wallToInternal + (1<<33 - 1) // year 2157 153 minWall = wallToInternal // year 1885 154 nsecMask = 1<<30 - 1 155 nsecShift = 30 156 ) 157 158 // These helpers for manipulating the wall and monotonic clock readings 159 // take pointer receivers, even when they don't modify the time, 160 // to make them cheaper to call. 161 162 // nsec returns the time's nanoseconds. 163 func (t *Time) nsec() int32 { 164 return int32(t.wall & nsecMask) 165 } 166 167 // sec returns the time's seconds since Jan 1 year 1. 168 func (t *Time) sec() int64 { 169 if t.wall&hasMonotonic != 0 { 170 return wallToInternal + int64(t.wall<<1>>(nsecShift+1)) 171 } 172 return t.ext 173 } 174 175 // unixSec returns the time's seconds since Jan 1 1970 (Unix time). 176 func (t *Time) unixSec() int64 { return t.sec() + internalToUnix } 177 178 // addSec adds d seconds to the time. 179 func (t *Time) addSec(d int64) { 180 if t.wall&hasMonotonic != 0 { 181 sec := int64(t.wall << 1 >> (nsecShift + 1)) 182 dsec := sec + d 183 if 0 <= dsec && dsec <= 1<<33-1 { 184 t.wall = t.wall&nsecMask | uint64(dsec)<<nsecShift | hasMonotonic 185 return 186 } 187 // Wall second now out of range for packed field. 188 // Move to ext. 189 t.stripMono() 190 } 191 192 // Check if the sum of t.ext and d overflows and handle it properly. 193 sum := t.ext + d 194 if (sum > t.ext) == (d > 0) { 195 t.ext = sum 196 } else if d > 0 { 197 t.ext = 1<<63 - 1 198 } else { 199 t.ext = -(1<<63 - 1) 200 } 201 } 202 203 // setLoc sets the location associated with the time. 204 func (t *Time) setLoc(loc *Location) { 205 if loc == &utcLoc { 206 loc = nil 207 } 208 t.stripMono() 209 t.loc = loc 210 } 211 212 // stripMono strips the monotonic clock reading in t. 213 func (t *Time) stripMono() { 214 if t.wall&hasMonotonic != 0 { 215 t.ext = t.sec() 216 t.wall &= nsecMask 217 } 218 } 219 220 // setMono sets the monotonic clock reading in t. 221 // If t cannot hold a monotonic clock reading, 222 // because its wall time is too large, 223 // setMono is a no-op. 224 func (t *Time) setMono(m int64) { 225 if t.wall&hasMonotonic == 0 { 226 sec := t.ext 227 if sec < minWall || maxWall < sec { 228 return 229 } 230 t.wall |= hasMonotonic | uint64(sec-minWall)<<nsecShift 231 } 232 t.ext = m 233 } 234 235 // mono returns t's monotonic clock reading. 236 // It returns 0 for a missing reading. 237 // This function is used only for testing, 238 // so it's OK that technically 0 is a valid 239 // monotonic clock reading as well. 240 func (t *Time) mono() int64 { 241 if t.wall&hasMonotonic == 0 { 242 return 0 243 } 244 return t.ext 245 } 246 247 // After reports whether the time instant t is after u. 248 func (t Time) After(u Time) bool { 249 if t.wall&u.wall&hasMonotonic != 0 { 250 return t.ext > u.ext 251 } 252 ts := t.sec() 253 us := u.sec() 254 return ts > us || ts == us && t.nsec() > u.nsec() 255 } 256 257 // Before reports whether the time instant t is before u. 258 func (t Time) Before(u Time) bool { 259 if t.wall&u.wall&hasMonotonic != 0 { 260 return t.ext < u.ext 261 } 262 ts := t.sec() 263 us := u.sec() 264 return ts < us || ts == us && t.nsec() < u.nsec() 265 } 266 267 // Equal reports whether t and u represent the same time instant. 268 // Two times can be equal even if they are in different locations. 269 // For example, 6:00 +0200 and 4:00 UTC are Equal. 270 // See the documentation on the Time type for the pitfalls of using == with 271 // Time values; most code should use Equal instead. 272 func (t Time) Equal(u Time) bool { 273 if t.wall&u.wall&hasMonotonic != 0 { 274 return t.ext == u.ext 275 } 276 return t.sec() == u.sec() && t.nsec() == u.nsec() 277 } 278 279 // A Month specifies a month of the year (January = 1, ...). 280 type Month int 281 282 const ( 283 January Month = 1 + iota 284 February 285 March 286 April 287 May 288 June 289 July 290 August 291 September 292 October 293 November 294 December 295 ) 296 297 // String returns the English name of the month ("January", "February", ...). 298 func (m Month) String() string { 299 if January <= m && m <= December { 300 return longMonthNames[m-1] 301 } 302 buf := make([]byte, 20) 303 n := fmtInt(buf, uint64(m)) 304 return "%!Month(" + string(buf[n:]) + ")" 305 } 306 307 // A Weekday specifies a day of the week (Sunday = 0, ...). 308 type Weekday int 309 310 const ( 311 Sunday Weekday = iota 312 Monday 313 Tuesday 314 Wednesday 315 Thursday 316 Friday 317 Saturday 318 ) 319 320 // String returns the English name of the day ("Sunday", "Monday", ...). 321 func (d Weekday) String() string { 322 if Sunday <= d && d <= Saturday { 323 return longDayNames[d] 324 } 325 buf := make([]byte, 20) 326 n := fmtInt(buf, uint64(d)) 327 return "%!Weekday(" + string(buf[n:]) + ")" 328 } 329 330 // Computations on time. 331 // 332 // The zero value for a Time is defined to be 333 // January 1, year 1, 00:00:00.000000000 UTC 334 // which (1) looks like a zero, or as close as you can get in a date 335 // (1-1-1 00:00:00 UTC), (2) is unlikely enough to arise in practice to 336 // be a suitable "not set" sentinel, unlike Jan 1 1970, and (3) has a 337 // non-negative year even in time zones west of UTC, unlike 1-1-0 338 // 00:00:00 UTC, which would be 12-31-(-1) 19:00:00 in New York. 339 // 340 // The zero Time value does not force a specific epoch for the time 341 // representation. For example, to use the Unix epoch internally, we 342 // could define that to distinguish a zero value from Jan 1 1970, that 343 // time would be represented by sec=-1, nsec=1e9. However, it does 344 // suggest a representation, namely using 1-1-1 00:00:00 UTC as the 345 // epoch, and that's what we do. 346 // 347 // The Add and Sub computations are oblivious to the choice of epoch. 348 // 349 // The presentation computations - year, month, minute, and so on - all 350 // rely heavily on division and modulus by positive constants. For 351 // calendrical calculations we want these divisions to round down, even 352 // for negative values, so that the remainder is always positive, but 353 // Go's division (like most hardware division instructions) rounds to 354 // zero. We can still do those computations and then adjust the result 355 // for a negative numerator, but it's annoying to write the adjustment 356 // over and over. Instead, we can change to a different epoch so long 357 // ago that all the times we care about will be positive, and then round 358 // to zero and round down coincide. These presentation routines already 359 // have to add the zone offset, so adding the translation to the 360 // alternate epoch is cheap. For example, having a non-negative time t 361 // means that we can write 362 // 363 // sec = t % 60 364 // 365 // instead of 366 // 367 // sec = t % 60 368 // if sec < 0 { 369 // sec += 60 370 // } 371 // 372 // everywhere. 373 // 374 // The calendar runs on an exact 400 year cycle: a 400-year calendar 375 // printed for 1970-2369 will apply as well to 2370-2769. Even the days 376 // of the week match up. It simplifies the computations to choose the 377 // cycle boundaries so that the exceptional years are always delayed as 378 // long as possible. That means choosing a year equal to 1 mod 400, so 379 // that the first leap year is the 4th year, the first missed leap year 380 // is the 100th year, and the missed missed leap year is the 400th year. 381 // So we'd prefer instead to print a calendar for 2001-2400 and reuse it 382 // for 2401-2800. 383 // 384 // Finally, it's convenient if the delta between the Unix epoch and 385 // long-ago epoch is representable by an int64 constant. 386 // 387 // These three considerations—choose an epoch as early as possible, that 388 // uses a year equal to 1 mod 400, and that is no more than 2⁶³ seconds 389 // earlier than 1970—bring us to the year -292277022399. We refer to 390 // this year as the absolute zero year, and to times measured as a uint64 391 // seconds since this year as absolute times. 392 // 393 // Times measured as an int64 seconds since the year 1—the representation 394 // used for Time's sec field—are called internal times. 395 // 396 // Times measured as an int64 seconds since the year 1970 are called Unix 397 // times. 398 // 399 // It is tempting to just use the year 1 as the absolute epoch, defining 400 // that the routines are only valid for years >= 1. However, the 401 // routines would then be invalid when displaying the epoch in time zones 402 // west of UTC, since it is year 0. It doesn't seem tenable to say that 403 // printing the zero time correctly isn't supported in half the time 404 // zones. By comparison, it's reasonable to mishandle some times in 405 // the year -292277022399. 406 // 407 // All this is opaque to clients of the API and can be changed if a 408 // better implementation presents itself. 409 410 const ( 411 // The unsigned zero year for internal calculations. 412 // Must be 1 mod 400, and times before it will not compute correctly, 413 // but otherwise can be changed at will. 414 absoluteZeroYear = -292277022399 415 416 // The year of the zero Time. 417 // Assumed by the unixToInternal computation below. 418 internalYear = 1 419 420 // Offsets to convert between internal and absolute or Unix times. 421 absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay 422 internalToAbsolute = -absoluteToInternal 423 424 unixToInternal int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay 425 internalToUnix int64 = -unixToInternal 426 427 wallToInternal int64 = (1884*365 + 1884/4 - 1884/100 + 1884/400) * secondsPerDay 428 ) 429 430 // IsZero reports whether t represents the zero time instant, 431 // January 1, year 1, 00:00:00 UTC. 432 func (t Time) IsZero() bool { 433 return t.sec() == 0 && t.nsec() == 0 434 } 435 436 // abs returns the time t as an absolute time, adjusted by the zone offset. 437 // It is called when computing a presentation property like Month or Hour. 438 func (t Time) abs() uint64 { 439 l := t.loc 440 // Avoid function calls when possible. 441 if l == nil || l == &localLoc { 442 l = l.get() 443 } 444 sec := t.unixSec() 445 if l != &utcLoc { 446 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 447 sec += int64(l.cacheZone.offset) 448 } else { 449 _, offset, _, _, _ := l.lookup(sec) 450 sec += int64(offset) 451 } 452 } 453 return uint64(sec + (unixToInternal + internalToAbsolute)) 454 } 455 456 // locabs is a combination of the Zone and abs methods, 457 // extracting both return values from a single zone lookup. 458 func (t Time) locabs() (name string, offset int, abs uint64) { 459 l := t.loc 460 if l == nil || l == &localLoc { 461 l = l.get() 462 } 463 // Avoid function call if we hit the local time cache. 464 sec := t.unixSec() 465 if l != &utcLoc { 466 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 467 name = l.cacheZone.name 468 offset = l.cacheZone.offset 469 } else { 470 name, offset, _, _, _ = l.lookup(sec) 471 } 472 sec += int64(offset) 473 } else { 474 name = "UTC" 475 } 476 abs = uint64(sec + (unixToInternal + internalToAbsolute)) 477 return 478 } 479 480 // Date returns the year, month, and day in which t occurs. 481 func (t Time) Date() (year int, month Month, day int) { 482 year, month, day, _ = t.date(true) 483 return 484 } 485 486 // Year returns the year in which t occurs. 487 func (t Time) Year() int { 488 year, _, _, _ := t.date(false) 489 return year 490 } 491 492 // Month returns the month of the year specified by t. 493 func (t Time) Month() Month { 494 _, month, _, _ := t.date(true) 495 return month 496 } 497 498 // Day returns the day of the month specified by t. 499 func (t Time) Day() int { 500 _, _, day, _ := t.date(true) 501 return day 502 } 503 504 // Weekday returns the day of the week specified by t. 505 func (t Time) Weekday() Weekday { 506 return absWeekday(t.abs()) 507 } 508 509 // absWeekday is like Weekday but operates on an absolute time. 510 func absWeekday(abs uint64) Weekday { 511 // January 1 of the absolute year, like January 1 of 2001, was a Monday. 512 sec := (abs + uint64(Monday)*secondsPerDay) % secondsPerWeek 513 return Weekday(int(sec) / secondsPerDay) 514 } 515 516 // ISOWeek returns the ISO 8601 year and week number in which t occurs. 517 // Week ranges from 1 to 53. Jan 01 to Jan 03 of year n might belong to 518 // week 52 or 53 of year n-1, and Dec 29 to Dec 31 might belong to week 1 519 // of year n+1. 520 func (t Time) ISOWeek() (year, week int) { 521 // According to the rule that the first calendar week of a calendar year is 522 // the week including the first Thursday of that year, and that the last one is 523 // the week immediately preceding the first calendar week of the next calendar year. 524 // See https://www.iso.org/obp/ui#iso:std:iso:8601:-1:ed-1:v1:en:term:3.1.1.23 for details. 525 526 // weeks start with Monday 527 // Monday Tuesday Wednesday Thursday Friday Saturday Sunday 528 // 1 2 3 4 5 6 7 529 // +3 +2 +1 0 -1 -2 -3 530 // the offset to Thursday 531 abs := t.abs() 532 d := Thursday - absWeekday(abs) 533 // handle Sunday 534 if d == 4 { 535 d = -3 536 } 537 // find the Thursday of the calendar week 538 abs += uint64(d) * secondsPerDay 539 year, _, _, yday := absDate(abs, false) 540 return year, yday/7 + 1 541 } 542 543 // Clock returns the hour, minute, and second within the day specified by t. 544 func (t Time) Clock() (hour, min, sec int) { 545 return absClock(t.abs()) 546 } 547 548 // absClock is like clock but operates on an absolute time. 549 func absClock(abs uint64) (hour, min, sec int) { 550 sec = int(abs % secondsPerDay) 551 hour = sec / secondsPerHour 552 sec -= hour * secondsPerHour 553 min = sec / secondsPerMinute 554 sec -= min * secondsPerMinute 555 return 556 } 557 558 // Hour returns the hour within the day specified by t, in the range [0, 23]. 559 func (t Time) Hour() int { 560 return int(t.abs()%secondsPerDay) / secondsPerHour 561 } 562 563 // Minute returns the minute offset within the hour specified by t, in the range [0, 59]. 564 func (t Time) Minute() int { 565 return int(t.abs()%secondsPerHour) / secondsPerMinute 566 } 567 568 // Second returns the second offset within the minute specified by t, in the range [0, 59]. 569 func (t Time) Second() int { 570 return int(t.abs() % secondsPerMinute) 571 } 572 573 // Nanosecond returns the nanosecond offset within the second specified by t, 574 // in the range [0, 999999999]. 575 func (t Time) Nanosecond() int { 576 return int(t.nsec()) 577 } 578 579 // YearDay returns the day of the year specified by t, in the range [1,365] for non-leap years, 580 // and [1,366] in leap years. 581 func (t Time) YearDay() int { 582 _, _, _, yday := t.date(false) 583 return yday + 1 584 } 585 586 // A Duration represents the elapsed time between two instants 587 // as an int64 nanosecond count. The representation limits the 588 // largest representable duration to approximately 290 years. 589 type Duration int64 590 591 const ( 592 minDuration Duration = -1 << 63 593 maxDuration Duration = 1<<63 - 1 594 ) 595 596 // Common durations. There is no definition for units of Day or larger 597 // to avoid confusion across daylight savings time zone transitions. 598 // 599 // To count the number of units in a Duration, divide: 600 // second := time.Second 601 // fmt.Print(int64(second/time.Millisecond)) // prints 1000 602 // 603 // To convert an integer number of units to a Duration, multiply: 604 // seconds := 10 605 // fmt.Print(time.Duration(seconds)*time.Second) // prints 10s 606 // 607 const ( 608 Nanosecond Duration = 1 609 Microsecond = 1000 * Nanosecond 610 Millisecond = 1000 * Microsecond 611 Second = 1000 * Millisecond 612 Minute = 60 * Second 613 Hour = 60 * Minute 614 ) 615 616 // String returns a string representing the duration in the form "72h3m0.5s". 617 // Leading zero units are omitted. As a special case, durations less than one 618 // second format use a smaller unit (milli-, micro-, or nanoseconds) to ensure 619 // that the leading digit is non-zero. The zero duration formats as 0s. 620 func (d Duration) String() string { 621 // Largest time is 2540400h10m10.000000000s 622 var buf [32]byte 623 w := len(buf) 624 625 u := uint64(d) 626 neg := d < 0 627 if neg { 628 u = -u 629 } 630 631 if u < uint64(Second) { 632 // Special case: if duration is smaller than a second, 633 // use smaller units, like 1.2ms 634 var prec int 635 w-- 636 buf[w] = 's' 637 w-- 638 switch { 639 case u == 0: 640 return "0s" 641 case u < uint64(Microsecond): 642 // print nanoseconds 643 prec = 0 644 buf[w] = 'n' 645 case u < uint64(Millisecond): 646 // print microseconds 647 prec = 3 648 // U+00B5 'µ' micro sign == 0xC2 0xB5 649 w-- // Need room for two bytes. 650 copy(buf[w:], "µ") 651 default: 652 // print milliseconds 653 prec = 6 654 buf[w] = 'm' 655 } 656 w, u = fmtFrac(buf[:w], u, prec) 657 w = fmtInt(buf[:w], u) 658 } else { 659 w-- 660 buf[w] = 's' 661 662 w, u = fmtFrac(buf[:w], u, 9) 663 664 // u is now integer seconds 665 w = fmtInt(buf[:w], u%60) 666 u /= 60 667 668 // u is now integer minutes 669 if u > 0 { 670 w-- 671 buf[w] = 'm' 672 w = fmtInt(buf[:w], u%60) 673 u /= 60 674 675 // u is now integer hours 676 // Stop at hours because days can be different lengths. 677 if u > 0 { 678 w-- 679 buf[w] = 'h' 680 w = fmtInt(buf[:w], u) 681 } 682 } 683 } 684 685 if neg { 686 w-- 687 buf[w] = '-' 688 } 689 690 return string(buf[w:]) 691 } 692 693 // fmtFrac formats the fraction of v/10**prec (e.g., ".12345") into the 694 // tail of buf, omitting trailing zeros. It omits the decimal 695 // point too when the fraction is 0. It returns the index where the 696 // output bytes begin and the value v/10**prec. 697 func fmtFrac(buf []byte, v uint64, prec int) (nw int, nv uint64) { 698 // Omit trailing zeros up to and including decimal point. 699 w := len(buf) 700 print := false 701 for i := 0; i < prec; i++ { 702 digit := v % 10 703 print = print || digit != 0 704 if print { 705 w-- 706 buf[w] = byte(digit) + '0' 707 } 708 v /= 10 709 } 710 if print { 711 w-- 712 buf[w] = '.' 713 } 714 return w, v 715 } 716 717 // fmtInt formats v into the tail of buf. 718 // It returns the index where the output begins. 719 func fmtInt(buf []byte, v uint64) int { 720 w := len(buf) 721 if v == 0 { 722 w-- 723 buf[w] = '0' 724 } else { 725 for v > 0 { 726 w-- 727 buf[w] = byte(v%10) + '0' 728 v /= 10 729 } 730 } 731 return w 732 } 733 734 // Nanoseconds returns the duration as an integer nanosecond count. 735 func (d Duration) Nanoseconds() int64 { return int64(d) } 736 737 // Microseconds returns the duration as an integer microsecond count. 738 func (d Duration) Microseconds() int64 { return int64(d) / 1e3 } 739 740 // Milliseconds returns the duration as an integer millisecond count. 741 func (d Duration) Milliseconds() int64 { return int64(d) / 1e6 } 742 743 // These methods return float64 because the dominant 744 // use case is for printing a floating point number like 1.5s, and 745 // a truncation to integer would make them not useful in those cases. 746 // Splitting the integer and fraction ourselves guarantees that 747 // converting the returned float64 to an integer rounds the same 748 // way that a pure integer conversion would have, even in cases 749 // where, say, float64(d.Nanoseconds())/1e9 would have rounded 750 // differently. 751 752 // Seconds returns the duration as a floating point number of seconds. 753 func (d Duration) Seconds() float64 { 754 sec := d / Second 755 nsec := d % Second 756 return float64(sec) + float64(nsec)/1e9 757 } 758 759 // Minutes returns the duration as a floating point number of minutes. 760 func (d Duration) Minutes() float64 { 761 min := d / Minute 762 nsec := d % Minute 763 return float64(min) + float64(nsec)/(60*1e9) 764 } 765 766 // Hours returns the duration as a floating point number of hours. 767 func (d Duration) Hours() float64 { 768 hour := d / Hour 769 nsec := d % Hour 770 return float64(hour) + float64(nsec)/(60*60*1e9) 771 } 772 773 // Truncate returns the result of rounding d toward zero to a multiple of m. 774 // If m <= 0, Truncate returns d unchanged. 775 func (d Duration) Truncate(m Duration) Duration { 776 if m <= 0 { 777 return d 778 } 779 return d - d%m 780 } 781 782 // lessThanHalf reports whether x+x < y but avoids overflow, 783 // assuming x and y are both positive (Duration is signed). 784 func lessThanHalf(x, y Duration) bool { 785 return uint64(x)+uint64(x) < uint64(y) 786 } 787 788 // Round returns the result of rounding d to the nearest multiple of m. 789 // The rounding behavior for halfway values is to round away from zero. 790 // If the result exceeds the maximum (or minimum) 791 // value that can be stored in a Duration, 792 // Round returns the maximum (or minimum) duration. 793 // If m <= 0, Round returns d unchanged. 794 func (d Duration) Round(m Duration) Duration { 795 if m <= 0 { 796 return d 797 } 798 r := d % m 799 if d < 0 { 800 r = -r 801 if lessThanHalf(r, m) { 802 return d + r 803 } 804 if d1 := d - m + r; d1 < d { 805 return d1 806 } 807 return minDuration // overflow 808 } 809 if lessThanHalf(r, m) { 810 return d - r 811 } 812 if d1 := d + m - r; d1 > d { 813 return d1 814 } 815 return maxDuration // overflow 816 } 817 818 // Add returns the time t+d. 819 func (t Time) Add(d Duration) Time { 820 dsec := int64(d / 1e9) 821 nsec := t.nsec() + int32(d%1e9) 822 if nsec >= 1e9 { 823 dsec++ 824 nsec -= 1e9 825 } else if nsec < 0 { 826 dsec-- 827 nsec += 1e9 828 } 829 t.wall = t.wall&^nsecMask | uint64(nsec) // update nsec 830 t.addSec(dsec) 831 if t.wall&hasMonotonic != 0 { 832 te := t.ext + int64(d) 833 if d < 0 && te > t.ext || d > 0 && te < t.ext { 834 // Monotonic clock reading now out of range; degrade to wall-only. 835 t.stripMono() 836 } else { 837 t.ext = te 838 } 839 } 840 return t 841 } 842 843 // Sub returns the duration t-u. If the result exceeds the maximum (or minimum) 844 // value that can be stored in a Duration, the maximum (or minimum) duration 845 // will be returned. 846 // To compute t-d for a duration d, use t.Add(-d). 847 func (t Time) Sub(u Time) Duration { 848 if t.wall&u.wall&hasMonotonic != 0 { 849 te := t.ext 850 ue := u.ext 851 d := Duration(te - ue) 852 if d < 0 && te > ue { 853 return maxDuration // t - u is positive out of range 854 } 855 if d > 0 && te < ue { 856 return minDuration // t - u is negative out of range 857 } 858 return d 859 } 860 d := Duration(t.sec()-u.sec())*Second + Duration(t.nsec()-u.nsec()) 861 // Check for overflow or underflow. 862 switch { 863 case u.Add(d).Equal(t): 864 return d // d is correct 865 case t.Before(u): 866 return minDuration // t - u is negative out of range 867 default: 868 return maxDuration // t - u is positive out of range 869 } 870 } 871 872 // Since returns the time elapsed since t. 873 // It is shorthand for time.Now().Sub(t). 874 func Since(t Time) Duration { 875 var now Time 876 if t.wall&hasMonotonic != 0 { 877 // Common case optimization: if t has monotonic time, then Sub will use only it. 878 now = Time{hasMonotonic, runtimeNano() - startNano, nil} 879 } else { 880 now = Now() 881 } 882 return now.Sub(t) 883 } 884 885 // Until returns the duration until t. 886 // It is shorthand for t.Sub(time.Now()). 887 func Until(t Time) Duration { 888 var now Time 889 if t.wall&hasMonotonic != 0 { 890 // Common case optimization: if t has monotonic time, then Sub will use only it. 891 now = Time{hasMonotonic, runtimeNano() - startNano, nil} 892 } else { 893 now = Now() 894 } 895 return t.Sub(now) 896 } 897 898 // AddDate returns the time corresponding to adding the 899 // given number of years, months, and days to t. 900 // For example, AddDate(-1, 2, 3) applied to January 1, 2011 901 // returns March 4, 2010. 902 // 903 // AddDate normalizes its result in the same way that Date does, 904 // so, for example, adding one month to October 31 yields 905 // December 1, the normalized form for November 31. 906 func (t Time) AddDate(years int, months int, days int) Time { 907 year, month, day := t.Date() 908 hour, min, sec := t.Clock() 909 return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec()), t.Location()) 910 } 911 912 const ( 913 secondsPerMinute = 60 914 secondsPerHour = 60 * secondsPerMinute 915 secondsPerDay = 24 * secondsPerHour 916 secondsPerWeek = 7 * secondsPerDay 917 daysPer400Years = 365*400 + 97 918 daysPer100Years = 365*100 + 24 919 daysPer4Years = 365*4 + 1 920 ) 921 922 // date computes the year, day of year, and when full=true, 923 // the month and day in which t occurs. 924 func (t Time) date(full bool) (year int, month Month, day int, yday int) { 925 return absDate(t.abs(), full) 926 } 927 928 // absDate is like date but operates on an absolute time. 929 func absDate(abs uint64, full bool) (year int, month Month, day int, yday int) { 930 // Split into time and day. 931 d := abs / secondsPerDay 932 933 // Account for 400 year cycles. 934 n := d / daysPer400Years 935 y := 400 * n 936 d -= daysPer400Years * n 937 938 // Cut off 100-year cycles. 939 // The last cycle has one extra leap year, so on the last day 940 // of that year, day / daysPer100Years will be 4 instead of 3. 941 // Cut it back down to 3 by subtracting n>>2. 942 n = d / daysPer100Years 943 n -= n >> 2 944 y += 100 * n 945 d -= daysPer100Years * n 946 947 // Cut off 4-year cycles. 948 // The last cycle has a missing leap year, which does not 949 // affect the computation. 950 n = d / daysPer4Years 951 y += 4 * n 952 d -= daysPer4Years * n 953 954 // Cut off years within a 4-year cycle. 955 // The last year is a leap year, so on the last day of that year, 956 // day / 365 will be 4 instead of 3. Cut it back down to 3 957 // by subtracting n>>2. 958 n = d / 365 959 n -= n >> 2 960 y += n 961 d -= 365 * n 962 963 year = int(int64(y) + absoluteZeroYear) 964 yday = int(d) 965 966 if !full { 967 return 968 } 969 970 day = yday 971 if isLeap(year) { 972 // Leap year 973 switch { 974 case day > 31+29-1: 975 // After leap day; pretend it wasn't there. 976 day-- 977 case day == 31+29-1: 978 // Leap day. 979 month = February 980 day = 29 981 return 982 } 983 } 984 985 // Estimate month on assumption that every month has 31 days. 986 // The estimate may be too low by at most one month, so adjust. 987 month = Month(day / 31) 988 end := int(daysBefore[month+1]) 989 var begin int 990 if day >= end { 991 month++ 992 begin = end 993 } else { 994 begin = int(daysBefore[month]) 995 } 996 997 month++ // because January is 1 998 day = day - begin + 1 999 return 1000 } 1001 1002 // daysBefore[m] counts the number of days in a non-leap year 1003 // before month m begins. There is an entry for m=12, counting 1004 // the number of days before January of next year (365). 1005 var daysBefore = [...]int32{ 1006 0, 1007 31, 1008 31 + 28, 1009 31 + 28 + 31, 1010 31 + 28 + 31 + 30, 1011 31 + 28 + 31 + 30 + 31, 1012 31 + 28 + 31 + 30 + 31 + 30, 1013 31 + 28 + 31 + 30 + 31 + 30 + 31, 1014 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31, 1015 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30, 1016 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31, 1017 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30, 1018 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31, 1019 } 1020 1021 func daysIn(m Month, year int) int { 1022 if m == February && isLeap(year) { 1023 return 29 1024 } 1025 return int(daysBefore[m] - daysBefore[m-1]) 1026 } 1027 1028 // daysSinceEpoch takes a year and returns the number of days from 1029 // the absolute epoch to the start of that year. 1030 // This is basically (year - zeroYear) * 365, but accounting for leap days. 1031 func daysSinceEpoch(year int) uint64 { 1032 y := uint64(int64(year) - absoluteZeroYear) 1033 1034 // Add in days from 400-year cycles. 1035 n := y / 400 1036 y -= 400 * n 1037 d := daysPer400Years * n 1038 1039 // Add in 100-year cycles. 1040 n = y / 100 1041 y -= 100 * n 1042 d += daysPer100Years * n 1043 1044 // Add in 4-year cycles. 1045 n = y / 4 1046 y -= 4 * n 1047 d += daysPer4Years * n 1048 1049 // Add in non-leap years. 1050 n = y 1051 d += 365 * n 1052 1053 return d 1054 } 1055 1056 // Provided by package runtime. 1057 func now() (sec int64, nsec int32, mono int64) 1058 1059 // runtimeNano returns the current value of the runtime clock in nanoseconds. 1060 //go:linkname runtimeNano runtime.nanotime 1061 func runtimeNano() int64 1062 1063 // Monotonic times are reported as offsets from startNano. 1064 // We initialize startNano to runtimeNano() - 1 so that on systems where 1065 // monotonic time resolution is fairly low (e.g. Windows 2008 1066 // which appears to have a default resolution of 15ms), 1067 // we avoid ever reporting a monotonic time of 0. 1068 // (Callers may want to use 0 as "time not set".) 1069 var startNano int64 = runtimeNano() - 1 1070 1071 // Now returns the current local time. 1072 func Now() Time { 1073 sec, nsec, mono := now() 1074 mono -= startNano 1075 sec += unixToInternal - minWall 1076 if uint64(sec)>>33 != 0 { 1077 return Time{uint64(nsec), sec + minWall, Local} 1078 } 1079 return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local} 1080 } 1081 1082 func unixTime(sec int64, nsec int32) Time { 1083 return Time{uint64(nsec), sec + unixToInternal, Local} 1084 } 1085 1086 // UTC returns t with the location set to UTC. 1087 func (t Time) UTC() Time { 1088 t.setLoc(&utcLoc) 1089 return t 1090 } 1091 1092 // Local returns t with the location set to local time. 1093 func (t Time) Local() Time { 1094 t.setLoc(Local) 1095 return t 1096 } 1097 1098 // In returns a copy of t representing the same time instant, but 1099 // with the copy's location information set to loc for display 1100 // purposes. 1101 // 1102 // In panics if loc is nil. 1103 func (t Time) In(loc *Location) Time { 1104 if loc == nil { 1105 panic("time: missing Location in call to Time.In") 1106 } 1107 t.setLoc(loc) 1108 return t 1109 } 1110 1111 // Location returns the time zone information associated with t. 1112 func (t Time) Location() *Location { 1113 l := t.loc 1114 if l == nil { 1115 l = UTC 1116 } 1117 return l 1118 } 1119 1120 // Zone computes the time zone in effect at time t, returning the abbreviated 1121 // name of the zone (such as "CET") and its offset in seconds east of UTC. 1122 func (t Time) Zone() (name string, offset int) { 1123 name, offset, _, _, _ = t.loc.lookup(t.unixSec()) 1124 return 1125 } 1126 1127 // Unix returns t as a Unix time, the number of seconds elapsed 1128 // since January 1, 1970 UTC. The result does not depend on the 1129 // location associated with t. 1130 // Unix-like operating systems often record time as a 32-bit 1131 // count of seconds, but since the method here returns a 64-bit 1132 // value it is valid for billions of years into the past or future. 1133 func (t Time) Unix() int64 { 1134 return t.unixSec() 1135 } 1136 1137 // UnixMilli returns t as a Unix time, the number of milliseconds elapsed since 1138 // January 1, 1970 UTC. The result is undefined if the Unix time in 1139 // milliseconds cannot be represented by an int64 (a date more than 292 million 1140 // years before or after 1970). The result does not depend on the 1141 // location associated with t. 1142 func (t Time) UnixMilli() int64 { 1143 return t.unixSec()*1e3 + int64(t.nsec())/1e6 1144 } 1145 1146 // UnixMicro returns t as a Unix time, the number of microseconds elapsed since 1147 // January 1, 1970 UTC. The result is undefined if the Unix time in 1148 // microseconds cannot be represented by an int64 (a date before year -290307 or 1149 // after year 294246). The result does not depend on the location associated 1150 // with t. 1151 func (t Time) UnixMicro() int64 { 1152 return t.unixSec()*1e6 + int64(t.nsec())/1e3 1153 } 1154 1155 // UnixNano returns t as a Unix time, the number of nanoseconds elapsed 1156 // since January 1, 1970 UTC. The result is undefined if the Unix time 1157 // in nanoseconds cannot be represented by an int64 (a date before the year 1158 // 1678 or after 2262). Note that this means the result of calling UnixNano 1159 // on the zero Time is undefined. The result does not depend on the 1160 // location associated with t. 1161 func (t Time) UnixNano() int64 { 1162 return (t.unixSec())*1e9 + int64(t.nsec()) 1163 } 1164 1165 const ( 1166 timeBinaryVersionV1 byte = iota + 1 // For general situation 1167 timeBinaryVersionV2 // For LMT only 1168 ) 1169 1170 // MarshalBinary implements the encoding.BinaryMarshaler interface. 1171 func (t Time) MarshalBinary() ([]byte, error) { 1172 var offsetMin int16 // minutes east of UTC. -1 is UTC. 1173 var offsetSec int8 1174 version := timeBinaryVersionV1 1175 1176 if t.Location() == UTC { 1177 offsetMin = -1 1178 } else { 1179 _, offset := t.Zone() 1180 if offset%60 != 0 { 1181 version = timeBinaryVersionV2 1182 offsetSec = int8(offset % 60) 1183 } 1184 1185 offset /= 60 1186 if offset < -32768 || offset == -1 || offset > 32767 { 1187 return nil, errors.New("Time.MarshalBinary: unexpected zone offset") 1188 } 1189 offsetMin = int16(offset) 1190 } 1191 1192 sec := t.sec() 1193 nsec := t.nsec() 1194 enc := []byte{ 1195 version, // byte 0 : version 1196 byte(sec >> 56), // bytes 1-8: seconds 1197 byte(sec >> 48), 1198 byte(sec >> 40), 1199 byte(sec >> 32), 1200 byte(sec >> 24), 1201 byte(sec >> 16), 1202 byte(sec >> 8), 1203 byte(sec), 1204 byte(nsec >> 24), // bytes 9-12: nanoseconds 1205 byte(nsec >> 16), 1206 byte(nsec >> 8), 1207 byte(nsec), 1208 byte(offsetMin >> 8), // bytes 13-14: zone offset in minutes 1209 byte(offsetMin), 1210 } 1211 if version == timeBinaryVersionV2 { 1212 enc = append(enc, byte(offsetSec)) 1213 } 1214 1215 return enc, nil 1216 } 1217 1218 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. 1219 func (t *Time) UnmarshalBinary(data []byte) error { 1220 buf := data 1221 if len(buf) == 0 { 1222 return errors.New("Time.UnmarshalBinary: no data") 1223 } 1224 1225 version := buf[0] 1226 if version != timeBinaryVersionV1 && version != timeBinaryVersionV2 { 1227 return errors.New("Time.UnmarshalBinary: unsupported version") 1228 } 1229 1230 wantLen := /*version*/ 1 + /*sec*/ 8 + /*nsec*/ 4 + /*zone offset*/ 2 1231 if version == timeBinaryVersionV2 { 1232 wantLen++ 1233 } 1234 if len(buf) != wantLen { 1235 return errors.New("Time.UnmarshalBinary: invalid length") 1236 } 1237 1238 buf = buf[1:] 1239 sec := int64(buf[7]) | int64(buf[6])<<8 | int64(buf[5])<<16 | int64(buf[4])<<24 | 1240 int64(buf[3])<<32 | int64(buf[2])<<40 | int64(buf[1])<<48 | int64(buf[0])<<56 1241 1242 buf = buf[8:] 1243 nsec := int32(buf[3]) | int32(buf[2])<<8 | int32(buf[1])<<16 | int32(buf[0])<<24 1244 1245 buf = buf[4:] 1246 offset := int(int16(buf[1])|int16(buf[0])<<8) * 60 1247 if version == timeBinaryVersionV2 { 1248 offset += int(buf[2]) 1249 } 1250 1251 *t = Time{} 1252 t.wall = uint64(nsec) 1253 t.ext = sec 1254 1255 if offset == -1*60 { 1256 t.setLoc(&utcLoc) 1257 } else if _, localoff, _, _, _ := Local.lookup(t.unixSec()); offset == localoff { 1258 t.setLoc(Local) 1259 } else { 1260 t.setLoc(FixedZone("", offset)) 1261 } 1262 1263 return nil 1264 } 1265 1266 // TODO(rsc): Remove GobEncoder, GobDecoder, MarshalJSON, UnmarshalJSON in Go 2. 1267 // The same semantics will be provided by the generic MarshalBinary, MarshalText, 1268 // UnmarshalBinary, UnmarshalText. 1269 1270 // GobEncode implements the gob.GobEncoder interface. 1271 func (t Time) GobEncode() ([]byte, error) { 1272 return t.MarshalBinary() 1273 } 1274 1275 // GobDecode implements the gob.GobDecoder interface. 1276 func (t *Time) GobDecode(data []byte) error { 1277 return t.UnmarshalBinary(data) 1278 } 1279 1280 // MarshalJSON implements the json.Marshaler interface. 1281 // The time is a quoted string in RFC 3339 format, with sub-second precision added if present. 1282 func (t Time) MarshalJSON() ([]byte, error) { 1283 if y := t.Year(); y < 0 || y >= 10000 { 1284 // RFC 3339 is clear that years are 4 digits exactly. 1285 // See golang.org/issue/4556#c15 for more discussion. 1286 return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]") 1287 } 1288 1289 b := make([]byte, 0, len(RFC3339Nano)+2) 1290 b = append(b, '"') 1291 b = t.AppendFormat(b, RFC3339Nano) 1292 b = append(b, '"') 1293 return b, nil 1294 } 1295 1296 // UnmarshalJSON implements the json.Unmarshaler interface. 1297 // The time is expected to be a quoted string in RFC 3339 format. 1298 func (t *Time) UnmarshalJSON(data []byte) error { 1299 // Ignore null, like in the main JSON package. 1300 if string(data) == "null" { 1301 return nil 1302 } 1303 // Fractional seconds are handled implicitly by Parse. 1304 var err error 1305 *t, err = Parse(`"`+RFC3339+`"`, string(data)) 1306 return err 1307 } 1308 1309 // MarshalText implements the encoding.TextMarshaler interface. 1310 // The time is formatted in RFC 3339 format, with sub-second precision added if present. 1311 func (t Time) MarshalText() ([]byte, error) { 1312 if y := t.Year(); y < 0 || y >= 10000 { 1313 return nil, errors.New("Time.MarshalText: year outside of range [0,9999]") 1314 } 1315 1316 b := make([]byte, 0, len(RFC3339Nano)) 1317 return t.AppendFormat(b, RFC3339Nano), nil 1318 } 1319 1320 // UnmarshalText implements the encoding.TextUnmarshaler interface. 1321 // The time is expected to be in RFC 3339 format. 1322 func (t *Time) UnmarshalText(data []byte) error { 1323 // Fractional seconds are handled implicitly by Parse. 1324 var err error 1325 *t, err = Parse(RFC3339, string(data)) 1326 return err 1327 } 1328 1329 // Unix returns the local Time corresponding to the given Unix time, 1330 // sec seconds and nsec nanoseconds since January 1, 1970 UTC. 1331 // It is valid to pass nsec outside the range [0, 999999999]. 1332 // Not all sec values have a corresponding time value. One such 1333 // value is 1<<63-1 (the largest int64 value). 1334 func Unix(sec int64, nsec int64) Time { 1335 if nsec < 0 || nsec >= 1e9 { 1336 n := nsec / 1e9 1337 sec += n 1338 nsec -= n * 1e9 1339 if nsec < 0 { 1340 nsec += 1e9 1341 sec-- 1342 } 1343 } 1344 return unixTime(sec, int32(nsec)) 1345 } 1346 1347 // UnixMilli returns the local Time corresponding to the given Unix time, 1348 // msec milliseconds since January 1, 1970 UTC. 1349 func UnixMilli(msec int64) Time { 1350 return Unix(msec/1e3, (msec%1e3)*1e6) 1351 } 1352 1353 // UnixMicro returns the local Time corresponding to the given Unix time, 1354 // usec microseconds since January 1, 1970 UTC. 1355 func UnixMicro(usec int64) Time { 1356 return Unix(usec/1e6, (usec%1e6)*1e3) 1357 } 1358 1359 // IsDST reports whether the time in the configured location is in Daylight Savings Time. 1360 func (t Time) IsDST() bool { 1361 _, _, _, _, isDST := t.loc.lookup(t.Unix()) 1362 return isDST 1363 } 1364 1365 func isLeap(year int) bool { 1366 return year%4 == 0 && (year%100 != 0 || year%400 == 0) 1367 } 1368 1369 // norm returns nhi, nlo such that 1370 // hi * base + lo == nhi * base + nlo 1371 // 0 <= nlo < base 1372 func norm(hi, lo, base int) (nhi, nlo int) { 1373 if lo < 0 { 1374 n := (-lo-1)/base + 1 1375 hi -= n 1376 lo += n * base 1377 } 1378 if lo >= base { 1379 n := lo / base 1380 hi += n 1381 lo -= n * base 1382 } 1383 return hi, lo 1384 } 1385 1386 // Date returns the Time corresponding to 1387 // yyyy-mm-dd hh:mm:ss + nsec nanoseconds 1388 // in the appropriate zone for that time in the given location. 1389 // 1390 // The month, day, hour, min, sec, and nsec values may be outside 1391 // their usual ranges and will be normalized during the conversion. 1392 // For example, October 32 converts to November 1. 1393 // 1394 // A daylight savings time transition skips or repeats times. 1395 // For example, in the United States, March 13, 2011 2:15am never occurred, 1396 // while November 6, 2011 1:15am occurred twice. In such cases, the 1397 // choice of time zone, and therefore the time, is not well-defined. 1398 // Date returns a time that is correct in one of the two zones involved 1399 // in the transition, but it does not guarantee which. 1400 // 1401 // Date panics if loc is nil. 1402 func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time { 1403 if loc == nil { 1404 panic("time: missing Location in call to Date") 1405 } 1406 1407 // Normalize month, overflowing into year. 1408 m := int(month) - 1 1409 year, m = norm(year, m, 12) 1410 month = Month(m) + 1 1411 1412 // Normalize nsec, sec, min, hour, overflowing into day. 1413 sec, nsec = norm(sec, nsec, 1e9) 1414 min, sec = norm(min, sec, 60) 1415 hour, min = norm(hour, min, 60) 1416 day, hour = norm(day, hour, 24) 1417 1418 // Compute days since the absolute epoch. 1419 d := daysSinceEpoch(year) 1420 1421 // Add in days before this month. 1422 d += uint64(daysBefore[month-1]) 1423 if isLeap(year) && month >= March { 1424 d++ // February 29 1425 } 1426 1427 // Add in days before today. 1428 d += uint64(day - 1) 1429 1430 // Add in time elapsed today. 1431 abs := d * secondsPerDay 1432 abs += uint64(hour*secondsPerHour + min*secondsPerMinute + sec) 1433 1434 unix := int64(abs) + (absoluteToInternal + internalToUnix) 1435 1436 // Look for zone offset for expected time, so we can adjust to UTC. 1437 // The lookup function expects UTC, so first we pass unix in the 1438 // hope that it will not be too close to a zone transition, 1439 // and then adjust if it is. 1440 _, offset, start, end, _ := loc.lookup(unix) 1441 if offset != 0 { 1442 utc := unix - int64(offset) 1443 // If utc is valid for the time zone we found, then we have the right offset. 1444 // If not, we get the correct offset by looking up utc in the location. 1445 if utc < start || utc >= end { 1446 _, offset, _, _, _ = loc.lookup(utc) 1447 } 1448 unix -= int64(offset) 1449 } 1450 1451 t := unixTime(unix, int32(nsec)) 1452 t.setLoc(loc) 1453 return t 1454 } 1455 1456 // Truncate returns the result of rounding t down to a multiple of d (since the zero time). 1457 // If d <= 0, Truncate returns t stripped of any monotonic clock reading but otherwise unchanged. 1458 // 1459 // Truncate operates on the time as an absolute duration since the 1460 // zero time; it does not operate on the presentation form of the 1461 // time. Thus, Truncate(Hour) may return a time with a non-zero 1462 // minute, depending on the time's Location. 1463 func (t Time) Truncate(d Duration) Time { 1464 t.stripMono() 1465 if d <= 0 { 1466 return t 1467 } 1468 _, r := div(t, d) 1469 return t.Add(-r) 1470 } 1471 1472 // Round returns the result of rounding t to the nearest multiple of d (since the zero time). 1473 // The rounding behavior for halfway values is to round up. 1474 // If d <= 0, Round returns t stripped of any monotonic clock reading but otherwise unchanged. 1475 // 1476 // Round operates on the time as an absolute duration since the 1477 // zero time; it does not operate on the presentation form of the 1478 // time. Thus, Round(Hour) may return a time with a non-zero 1479 // minute, depending on the time's Location. 1480 func (t Time) Round(d Duration) Time { 1481 t.stripMono() 1482 if d <= 0 { 1483 return t 1484 } 1485 _, r := div(t, d) 1486 if lessThanHalf(r, d) { 1487 return t.Add(-r) 1488 } 1489 return t.Add(d - r) 1490 } 1491 1492 // div divides t by d and returns the quotient parity and remainder. 1493 // We don't use the quotient parity anymore (round half up instead of round to even) 1494 // but it's still here in case we change our minds. 1495 func div(t Time, d Duration) (qmod2 int, r Duration) { 1496 neg := false 1497 nsec := t.nsec() 1498 sec := t.sec() 1499 if sec < 0 { 1500 // Operate on absolute value. 1501 neg = true 1502 sec = -sec 1503 nsec = -nsec 1504 if nsec < 0 { 1505 nsec += 1e9 1506 sec-- // sec >= 1 before the -- so safe 1507 } 1508 } 1509 1510 switch { 1511 // Special case: 2d divides 1 second. 1512 case d < Second && Second%(d+d) == 0: 1513 qmod2 = int(nsec/int32(d)) & 1 1514 r = Duration(nsec % int32(d)) 1515 1516 // Special case: d is a multiple of 1 second. 1517 case d%Second == 0: 1518 d1 := int64(d / Second) 1519 qmod2 = int(sec/d1) & 1 1520 r = Duration(sec%d1)*Second + Duration(nsec) 1521 1522 // General case. 1523 // This could be faster if more cleverness were applied, 1524 // but it's really only here to avoid special case restrictions in the API. 1525 // No one will care about these cases. 1526 default: 1527 // Compute nanoseconds as 128-bit number. 1528 sec := uint64(sec) 1529 tmp := (sec >> 32) * 1e9 1530 u1 := tmp >> 32 1531 u0 := tmp << 32 1532 tmp = (sec & 0xFFFFFFFF) * 1e9 1533 u0x, u0 := u0, u0+tmp 1534 if u0 < u0x { 1535 u1++ 1536 } 1537 u0x, u0 = u0, u0+uint64(nsec) 1538 if u0 < u0x { 1539 u1++ 1540 } 1541 1542 // Compute remainder by subtracting r<<k for decreasing k. 1543 // Quotient parity is whether we subtract on last round. 1544 d1 := uint64(d) 1545 for d1>>63 != 1 { 1546 d1 <<= 1 1547 } 1548 d0 := uint64(0) 1549 for { 1550 qmod2 = 0 1551 if u1 > d1 || u1 == d1 && u0 >= d0 { 1552 // subtract 1553 qmod2 = 1 1554 u0x, u0 = u0, u0-d0 1555 if u0 > u0x { 1556 u1-- 1557 } 1558 u1 -= d1 1559 } 1560 if d1 == 0 && d0 == uint64(d) { 1561 break 1562 } 1563 d0 >>= 1 1564 d0 |= (d1 & 1) << 63 1565 d1 >>= 1 1566 } 1567 r = Duration(u0) 1568 } 1569 1570 if neg && r != 0 { 1571 // If input was negative and not an exact multiple of d, we computed q, r such that 1572 // q*d + r = -t 1573 // But the right answers are given by -(q-1), d-r: 1574 // q*d + r = -t 1575 // -q*d - r = t 1576 // -(q-1)*d + (d - r) = t 1577 qmod2 ^= 1 1578 r = d - r 1579 } 1580 return 1581 } 1582