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), t.Compare(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. The same applies to other functions and 57 // methods that subtract times, such as [Since], [Until], [Before], [After], 58 // [Add], [Sub], [Equal] and [Compare]. In some cases, you may need to strip 59 // the monotonic clock to get accurate results. 60 // 61 // Because the monotonic clock reading has no meaning outside 62 // the current process, the serialized forms generated by t.GobEncode, 63 // t.MarshalBinary, t.MarshalJSON, and t.MarshalText omit the monotonic 64 // clock reading, and t.Format provides no format for it. Similarly, the 65 // constructors [time.Date], [time.Parse], [time.ParseInLocation], and [time.Unix], 66 // as well as the unmarshalers t.GobDecode, t.UnmarshalBinary. 67 // t.UnmarshalJSON, and t.UnmarshalText always create times with 68 // no monotonic clock reading. 69 // 70 // The monotonic clock reading exists only in [Time] values. It is not 71 // a part of [Duration] values or the Unix times returned by t.Unix and 72 // friends. 73 // 74 // Note that the Go == operator compares not just the time instant but 75 // also the [Location] and the monotonic clock reading. See the 76 // documentation for the Time type for a discussion of equality 77 // testing for Time values. 78 // 79 // For debugging, the result of t.String does include the monotonic 80 // clock reading if present. If t != u because of different monotonic clock readings, 81 // that difference will be visible when printing t.String() and u.String(). 82 // 83 // # Timer Resolution 84 // 85 // [Timer] resolution varies depending on the Go runtime, the operating system 86 // and the underlying hardware. 87 // On Unix, the resolution is ~1ms. 88 // On Windows version 1803 and newer, the resolution is ~0.5ms. 89 // On older Windows versions, the default resolution is ~16ms, but 90 // a higher resolution may be requested using [golang.org/x/sys/windows.TimeBeginPeriod]. 91 package time 92 93 import ( 94 "errors" 95 _ "unsafe" // for go:linkname 96 ) 97 98 // A Time represents an instant in time with nanosecond precision. 99 // 100 // Programs using times should typically store and pass them as values, 101 // not pointers. That is, time variables and struct fields should be of 102 // type [time.Time], not *time.Time. 103 // 104 // A Time value can be used by multiple goroutines simultaneously except 105 // that the methods [Time.GobDecode], [Time.UnmarshalBinary], [Time.UnmarshalJSON] and 106 // [Time.UnmarshalText] are not concurrency-safe. 107 // 108 // Time instants can be compared using the [Time.Before], [Time.After], and [Time.Equal] methods. 109 // The [Time.Sub] method subtracts two instants, producing a [Duration]. 110 // The [Time.Add] method adds a Time and a Duration, producing a Time. 111 // 112 // The zero value of type Time is January 1, year 1, 00:00:00.000000000 UTC. 113 // As this time is unlikely to come up in practice, the [Time.IsZero] method gives 114 // a simple way of detecting a time that has not been initialized explicitly. 115 // 116 // Each time has an associated [Location]. The methods [Time.Local], [Time.UTC], and Time.In return a 117 // Time with a specific Location. Changing the Location of a Time value with 118 // these methods does not change the actual instant it represents, only the time 119 // zone in which to interpret it. 120 // 121 // Representations of a Time value saved by the [Time.GobEncode], [Time.MarshalBinary], 122 // [Time.MarshalJSON], and [Time.MarshalText] methods store the [Time.Location]'s offset, but not 123 // the location name. They therefore lose information about Daylight Saving Time. 124 // 125 // In addition to the required “wall clock” reading, a Time may contain an optional 126 // reading of the current process's monotonic clock, to provide additional precision 127 // for comparison or subtraction. 128 // See the “Monotonic Clocks” section in the package documentation for details. 129 // 130 // Note that the Go == operator compares not just the time instant but also the 131 // Location and the monotonic clock reading. Therefore, Time values should not 132 // be used as map or database keys without first guaranteeing that the 133 // identical Location has been set for all values, which can be achieved 134 // through use of the UTC or Local method, and that the monotonic clock reading 135 // has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u) 136 // to t == u, since t.Equal uses the most accurate comparison available and 137 // correctly handles the case when only one of its arguments has a monotonic 138 // clock reading. 139 type Time struct { 140 // wall and ext encode the wall time seconds, wall time nanoseconds, 141 // and optional monotonic clock reading in nanoseconds. 142 // 143 // From high to low bit position, wall encodes a 1-bit flag (hasMonotonic), 144 // a 33-bit seconds field, and a 30-bit wall time nanoseconds field. 145 // The nanoseconds field is in the range [0, 999999999]. 146 // If the hasMonotonic bit is 0, then the 33-bit field must be zero 147 // and the full signed 64-bit wall seconds since Jan 1 year 1 is stored in ext. 148 // If the hasMonotonic bit is 1, then the 33-bit field holds a 33-bit 149 // unsigned wall seconds since Jan 1 year 1885, and ext holds a 150 // signed 64-bit monotonic clock reading, nanoseconds since process start. 151 wall uint64 152 ext int64 153 154 // loc specifies the Location that should be used to 155 // determine the minute, hour, month, day, and year 156 // that correspond to this Time. 157 // The nil location means UTC. 158 // All UTC times are represented with loc==nil, never loc==&utcLoc. 159 loc *Location 160 } 161 162 const ( 163 hasMonotonic = 1 << 63 164 maxWall = wallToInternal + (1<<33 - 1) // year 2157 165 minWall = wallToInternal // year 1885 166 nsecMask = 1<<30 - 1 167 nsecShift = 30 168 ) 169 170 // These helpers for manipulating the wall and monotonic clock readings 171 // take pointer receivers, even when they don't modify the time, 172 // to make them cheaper to call. 173 174 // nsec returns the time's nanoseconds. 175 func (t *Time) nsec() int32 { 176 return int32(t.wall & nsecMask) 177 } 178 179 // sec returns the time's seconds since Jan 1 year 1. 180 func (t *Time) sec() int64 { 181 if t.wall&hasMonotonic != 0 { 182 return wallToInternal + int64(t.wall<<1>>(nsecShift+1)) 183 } 184 return t.ext 185 } 186 187 // unixSec returns the time's seconds since Jan 1 1970 (Unix time). 188 func (t *Time) unixSec() int64 { return t.sec() + internalToUnix } 189 190 // addSec adds d seconds to the time. 191 func (t *Time) addSec(d int64) { 192 if t.wall&hasMonotonic != 0 { 193 sec := int64(t.wall << 1 >> (nsecShift + 1)) 194 dsec := sec + d 195 if 0 <= dsec && dsec <= 1<<33-1 { 196 t.wall = t.wall&nsecMask | uint64(dsec)<<nsecShift | hasMonotonic 197 return 198 } 199 // Wall second now out of range for packed field. 200 // Move to ext. 201 t.stripMono() 202 } 203 204 // Check if the sum of t.ext and d overflows and handle it properly. 205 sum := t.ext + d 206 if (sum > t.ext) == (d > 0) { 207 t.ext = sum 208 } else if d > 0 { 209 t.ext = 1<<63 - 1 210 } else { 211 t.ext = -(1<<63 - 1) 212 } 213 } 214 215 // setLoc sets the location associated with the time. 216 func (t *Time) setLoc(loc *Location) { 217 if loc == &utcLoc { 218 loc = nil 219 } 220 t.stripMono() 221 t.loc = loc 222 } 223 224 // stripMono strips the monotonic clock reading in t. 225 func (t *Time) stripMono() { 226 if t.wall&hasMonotonic != 0 { 227 t.ext = t.sec() 228 t.wall &= nsecMask 229 } 230 } 231 232 // setMono sets the monotonic clock reading in t. 233 // If t cannot hold a monotonic clock reading, 234 // because its wall time is too large, 235 // setMono is a no-op. 236 func (t *Time) setMono(m int64) { 237 if t.wall&hasMonotonic == 0 { 238 sec := t.ext 239 if sec < minWall || maxWall < sec { 240 return 241 } 242 t.wall |= hasMonotonic | uint64(sec-minWall)<<nsecShift 243 } 244 t.ext = m 245 } 246 247 // mono returns t's monotonic clock reading. 248 // It returns 0 for a missing reading. 249 // This function is used only for testing, 250 // so it's OK that technically 0 is a valid 251 // monotonic clock reading as well. 252 func (t *Time) mono() int64 { 253 if t.wall&hasMonotonic == 0 { 254 return 0 255 } 256 return t.ext 257 } 258 259 // After reports whether the time instant t is after u. 260 func (t Time) After(u Time) bool { 261 if t.wall&u.wall&hasMonotonic != 0 { 262 return t.ext > u.ext 263 } 264 ts := t.sec() 265 us := u.sec() 266 return ts > us || ts == us && t.nsec() > u.nsec() 267 } 268 269 // Before reports whether the time instant t is before u. 270 func (t Time) Before(u Time) bool { 271 if t.wall&u.wall&hasMonotonic != 0 { 272 return t.ext < u.ext 273 } 274 ts := t.sec() 275 us := u.sec() 276 return ts < us || ts == us && t.nsec() < u.nsec() 277 } 278 279 // Compare compares the time instant t with u. If t is before u, it returns -1; 280 // if t is after u, it returns +1; if they're the same, it returns 0. 281 func (t Time) Compare(u Time) int { 282 var tc, uc int64 283 if t.wall&u.wall&hasMonotonic != 0 { 284 tc, uc = t.ext, u.ext 285 } else { 286 tc, uc = t.sec(), u.sec() 287 if tc == uc { 288 tc, uc = int64(t.nsec()), int64(u.nsec()) 289 } 290 } 291 switch { 292 case tc < uc: 293 return -1 294 case tc > uc: 295 return +1 296 } 297 return 0 298 } 299 300 // Equal reports whether t and u represent the same time instant. 301 // Two times can be equal even if they are in different locations. 302 // For example, 6:00 +0200 and 4:00 UTC are Equal. 303 // See the documentation on the Time type for the pitfalls of using == with 304 // Time values; most code should use Equal instead. 305 func (t Time) Equal(u Time) bool { 306 if t.wall&u.wall&hasMonotonic != 0 { 307 return t.ext == u.ext 308 } 309 return t.sec() == u.sec() && t.nsec() == u.nsec() 310 } 311 312 // A Month specifies a month of the year (January = 1, ...). 313 type Month int 314 315 const ( 316 January Month = 1 + iota 317 February 318 March 319 April 320 May 321 June 322 July 323 August 324 September 325 October 326 November 327 December 328 ) 329 330 // String returns the English name of the month ("January", "February", ...). 331 func (m Month) String() string { 332 if January <= m && m <= December { 333 return longMonthNames[m-1] 334 } 335 buf := make([]byte, 20) 336 n := fmtInt(buf, uint64(m)) 337 return "%!Month(" + string(buf[n:]) + ")" 338 } 339 340 // A Weekday specifies a day of the week (Sunday = 0, ...). 341 type Weekday int 342 343 const ( 344 Sunday Weekday = iota 345 Monday 346 Tuesday 347 Wednesday 348 Thursday 349 Friday 350 Saturday 351 ) 352 353 // String returns the English name of the day ("Sunday", "Monday", ...). 354 func (d Weekday) String() string { 355 if Sunday <= d && d <= Saturday { 356 return longDayNames[d] 357 } 358 buf := make([]byte, 20) 359 n := fmtInt(buf, uint64(d)) 360 return "%!Weekday(" + string(buf[n:]) + ")" 361 } 362 363 // Computations on time. 364 // 365 // The zero value for a Time is defined to be 366 // January 1, year 1, 00:00:00.000000000 UTC 367 // which (1) looks like a zero, or as close as you can get in a date 368 // (1-1-1 00:00:00 UTC), (2) is unlikely enough to arise in practice to 369 // be a suitable "not set" sentinel, unlike Jan 1 1970, and (3) has a 370 // non-negative year even in time zones west of UTC, unlike 1-1-0 371 // 00:00:00 UTC, which would be 12-31-(-1) 19:00:00 in New York. 372 // 373 // The zero Time value does not force a specific epoch for the time 374 // representation. For example, to use the Unix epoch internally, we 375 // could define that to distinguish a zero value from Jan 1 1970, that 376 // time would be represented by sec=-1, nsec=1e9. However, it does 377 // suggest a representation, namely using 1-1-1 00:00:00 UTC as the 378 // epoch, and that's what we do. 379 // 380 // The Add and Sub computations are oblivious to the choice of epoch. 381 // 382 // The presentation computations - year, month, minute, and so on - all 383 // rely heavily on division and modulus by positive constants. For 384 // calendrical calculations we want these divisions to round down, even 385 // for negative values, so that the remainder is always positive, but 386 // Go's division (like most hardware division instructions) rounds to 387 // zero. We can still do those computations and then adjust the result 388 // for a negative numerator, but it's annoying to write the adjustment 389 // over and over. Instead, we can change to a different epoch so long 390 // ago that all the times we care about will be positive, and then round 391 // to zero and round down coincide. These presentation routines already 392 // have to add the zone offset, so adding the translation to the 393 // alternate epoch is cheap. For example, having a non-negative time t 394 // means that we can write 395 // 396 // sec = t % 60 397 // 398 // instead of 399 // 400 // sec = t % 60 401 // if sec < 0 { 402 // sec += 60 403 // } 404 // 405 // everywhere. 406 // 407 // The calendar runs on an exact 400 year cycle: a 400-year calendar 408 // printed for 1970-2369 will apply as well to 2370-2769. Even the days 409 // of the week match up. It simplifies the computations to choose the 410 // cycle boundaries so that the exceptional years are always delayed as 411 // long as possible. That means choosing a year equal to 1 mod 400, so 412 // that the first leap year is the 4th year, the first missed leap year 413 // is the 100th year, and the missed missed leap year is the 400th year. 414 // So we'd prefer instead to print a calendar for 2001-2400 and reuse it 415 // for 2401-2800. 416 // 417 // Finally, it's convenient if the delta between the Unix epoch and 418 // long-ago epoch is representable by an int64 constant. 419 // 420 // These three considerations—choose an epoch as early as possible, that 421 // uses a year equal to 1 mod 400, and that is no more than 2⁶³ seconds 422 // earlier than 1970—bring us to the year -292277022399. We refer to 423 // this year as the absolute zero year, and to times measured as a uint64 424 // seconds since this year as absolute times. 425 // 426 // Times measured as an int64 seconds since the year 1—the representation 427 // used for Time's sec field—are called internal times. 428 // 429 // Times measured as an int64 seconds since the year 1970 are called Unix 430 // times. 431 // 432 // It is tempting to just use the year 1 as the absolute epoch, defining 433 // that the routines are only valid for years >= 1. However, the 434 // routines would then be invalid when displaying the epoch in time zones 435 // west of UTC, since it is year 0. It doesn't seem tenable to say that 436 // printing the zero time correctly isn't supported in half the time 437 // zones. By comparison, it's reasonable to mishandle some times in 438 // the year -292277022399. 439 // 440 // All this is opaque to clients of the API and can be changed if a 441 // better implementation presents itself. 442 443 const ( 444 // The unsigned zero year for internal calculations. 445 // Must be 1 mod 400, and times before it will not compute correctly, 446 // but otherwise can be changed at will. 447 absoluteZeroYear = -292277022399 448 449 // The year of the zero Time. 450 // Assumed by the unixToInternal computation below. 451 internalYear = 1 452 453 // Offsets to convert between internal and absolute or Unix times. 454 absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay 455 internalToAbsolute = -absoluteToInternal 456 457 unixToInternal int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay 458 internalToUnix int64 = -unixToInternal 459 460 wallToInternal int64 = (1884*365 + 1884/4 - 1884/100 + 1884/400) * secondsPerDay 461 ) 462 463 // IsZero reports whether t represents the zero time instant, 464 // January 1, year 1, 00:00:00 UTC. 465 func (t Time) IsZero() bool { 466 return t.sec() == 0 && t.nsec() == 0 467 } 468 469 // abs returns the time t as an absolute time, adjusted by the zone offset. 470 // It is called when computing a presentation property like Month or Hour. 471 func (t Time) abs() uint64 { 472 l := t.loc 473 // Avoid function calls when possible. 474 if l == nil || l == &localLoc { 475 l = l.get() 476 } 477 sec := t.unixSec() 478 if l != &utcLoc { 479 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 480 sec += int64(l.cacheZone.offset) 481 } else { 482 _, offset, _, _, _ := l.lookup(sec) 483 sec += int64(offset) 484 } 485 } 486 return uint64(sec + (unixToInternal + internalToAbsolute)) 487 } 488 489 // locabs is a combination of the Zone and abs methods, 490 // extracting both return values from a single zone lookup. 491 func (t Time) locabs() (name string, offset int, abs uint64) { 492 l := t.loc 493 if l == nil || l == &localLoc { 494 l = l.get() 495 } 496 // Avoid function call if we hit the local time cache. 497 sec := t.unixSec() 498 if l != &utcLoc { 499 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 500 name = l.cacheZone.name 501 offset = l.cacheZone.offset 502 } else { 503 name, offset, _, _, _ = l.lookup(sec) 504 } 505 sec += int64(offset) 506 } else { 507 name = "UTC" 508 } 509 abs = uint64(sec + (unixToInternal + internalToAbsolute)) 510 return 511 } 512 513 // Date returns the year, month, and day in which t occurs. 514 func (t Time) Date() (year int, month Month, day int) { 515 year, month, day, _ = t.date(true) 516 return 517 } 518 519 // Year returns the year in which t occurs. 520 func (t Time) Year() int { 521 year, _, _, _ := t.date(false) 522 return year 523 } 524 525 // Month returns the month of the year specified by t. 526 func (t Time) Month() Month { 527 _, month, _, _ := t.date(true) 528 return month 529 } 530 531 // Day returns the day of the month specified by t. 532 func (t Time) Day() int { 533 _, _, day, _ := t.date(true) 534 return day 535 } 536 537 // Weekday returns the day of the week specified by t. 538 func (t Time) Weekday() Weekday { 539 return absWeekday(t.abs()) 540 } 541 542 // absWeekday is like Weekday but operates on an absolute time. 543 func absWeekday(abs uint64) Weekday { 544 // January 1 of the absolute year, like January 1 of 2001, was a Monday. 545 sec := (abs + uint64(Monday)*secondsPerDay) % secondsPerWeek 546 return Weekday(int(sec) / secondsPerDay) 547 } 548 549 // ISOWeek returns the ISO 8601 year and week number in which t occurs. 550 // Week ranges from 1 to 53. Jan 01 to Jan 03 of year n might belong to 551 // week 52 or 53 of year n-1, and Dec 29 to Dec 31 might belong to week 1 552 // of year n+1. 553 func (t Time) ISOWeek() (year, week int) { 554 // According to the rule that the first calendar week of a calendar year is 555 // the week including the first Thursday of that year, and that the last one is 556 // the week immediately preceding the first calendar week of the next calendar year. 557 // See https://www.iso.org/obp/ui#iso:std:iso:8601:-1:ed-1:v1:en:term:3.1.1.23 for details. 558 559 // weeks start with Monday 560 // Monday Tuesday Wednesday Thursday Friday Saturday Sunday 561 // 1 2 3 4 5 6 7 562 // +3 +2 +1 0 -1 -2 -3 563 // the offset to Thursday 564 abs := t.abs() 565 d := Thursday - absWeekday(abs) 566 // handle Sunday 567 if d == 4 { 568 d = -3 569 } 570 // find the Thursday of the calendar week 571 abs += uint64(d) * secondsPerDay 572 year, _, _, yday := absDate(abs, false) 573 return year, yday/7 + 1 574 } 575 576 // Clock returns the hour, minute, and second within the day specified by t. 577 func (t Time) Clock() (hour, min, sec int) { 578 return absClock(t.abs()) 579 } 580 581 // absClock is like clock but operates on an absolute time. 582 func absClock(abs uint64) (hour, min, sec int) { 583 sec = int(abs % secondsPerDay) 584 hour = sec / secondsPerHour 585 sec -= hour * secondsPerHour 586 min = sec / secondsPerMinute 587 sec -= min * secondsPerMinute 588 return 589 } 590 591 // Hour returns the hour within the day specified by t, in the range [0, 23]. 592 func (t Time) Hour() int { 593 return int(t.abs()%secondsPerDay) / secondsPerHour 594 } 595 596 // Minute returns the minute offset within the hour specified by t, in the range [0, 59]. 597 func (t Time) Minute() int { 598 return int(t.abs()%secondsPerHour) / secondsPerMinute 599 } 600 601 // Second returns the second offset within the minute specified by t, in the range [0, 59]. 602 func (t Time) Second() int { 603 return int(t.abs() % secondsPerMinute) 604 } 605 606 // Nanosecond returns the nanosecond offset within the second specified by t, 607 // in the range [0, 999999999]. 608 func (t Time) Nanosecond() int { 609 return int(t.nsec()) 610 } 611 612 // YearDay returns the day of the year specified by t, in the range [1,365] for non-leap years, 613 // and [1,366] in leap years. 614 func (t Time) YearDay() int { 615 _, _, _, yday := t.date(false) 616 return yday + 1 617 } 618 619 // A Duration represents the elapsed time between two instants 620 // as an int64 nanosecond count. The representation limits the 621 // largest representable duration to approximately 290 years. 622 type Duration int64 623 624 const ( 625 minDuration Duration = -1 << 63 626 maxDuration Duration = 1<<63 - 1 627 ) 628 629 // Common durations. There is no definition for units of Day or larger 630 // to avoid confusion across daylight savings time zone transitions. 631 // 632 // To count the number of units in a [Duration], divide: 633 // 634 // second := time.Second 635 // fmt.Print(int64(second/time.Millisecond)) // prints 1000 636 // 637 // To convert an integer number of units to a Duration, multiply: 638 // 639 // seconds := 10 640 // fmt.Print(time.Duration(seconds)*time.Second) // prints 10s 641 const ( 642 Nanosecond Duration = 1 643 Microsecond = 1000 * Nanosecond 644 Millisecond = 1000 * Microsecond 645 Second = 1000 * Millisecond 646 Minute = 60 * Second 647 Hour = 60 * Minute 648 ) 649 650 // String returns a string representing the duration in the form "72h3m0.5s". 651 // Leading zero units are omitted. As a special case, durations less than one 652 // second format use a smaller unit (milli-, micro-, or nanoseconds) to ensure 653 // that the leading digit is non-zero. The zero duration formats as 0s. 654 func (d Duration) String() string { 655 // This is inlinable to take advantage of "function outlining". 656 // Thus, the caller can decide whether a string must be heap allocated. 657 var arr [32]byte 658 n := d.format(&arr) 659 return string(arr[n:]) 660 } 661 662 // format formats the representation of d into the end of buf and 663 // returns the offset of the first character. 664 func (d Duration) format(buf *[32]byte) int { 665 // Largest time is 2540400h10m10.000000000s 666 w := len(buf) 667 668 u := uint64(d) 669 neg := d < 0 670 if neg { 671 u = -u 672 } 673 674 if u < uint64(Second) { 675 // Special case: if duration is smaller than a second, 676 // use smaller units, like 1.2ms 677 var prec int 678 w-- 679 buf[w] = 's' 680 w-- 681 switch { 682 case u == 0: 683 buf[w] = '0' 684 return w 685 case u < uint64(Microsecond): 686 // print nanoseconds 687 prec = 0 688 buf[w] = 'n' 689 case u < uint64(Millisecond): 690 // print microseconds 691 prec = 3 692 // U+00B5 'µ' micro sign == 0xC2 0xB5 693 w-- // Need room for two bytes. 694 copy(buf[w:], "µ") 695 default: 696 // print milliseconds 697 prec = 6 698 buf[w] = 'm' 699 } 700 w, u = fmtFrac(buf[:w], u, prec) 701 w = fmtInt(buf[:w], u) 702 } else { 703 w-- 704 buf[w] = 's' 705 706 w, u = fmtFrac(buf[:w], u, 9) 707 708 // u is now integer seconds 709 w = fmtInt(buf[:w], u%60) 710 u /= 60 711 712 // u is now integer minutes 713 if u > 0 { 714 w-- 715 buf[w] = 'm' 716 w = fmtInt(buf[:w], u%60) 717 u /= 60 718 719 // u is now integer hours 720 // Stop at hours because days can be different lengths. 721 if u > 0 { 722 w-- 723 buf[w] = 'h' 724 w = fmtInt(buf[:w], u) 725 } 726 } 727 } 728 729 if neg { 730 w-- 731 buf[w] = '-' 732 } 733 734 return w 735 } 736 737 // fmtFrac formats the fraction of v/10**prec (e.g., ".12345") into the 738 // tail of buf, omitting trailing zeros. It omits the decimal 739 // point too when the fraction is 0. It returns the index where the 740 // output bytes begin and the value v/10**prec. 741 func fmtFrac(buf []byte, v uint64, prec int) (nw int, nv uint64) { 742 // Omit trailing zeros up to and including decimal point. 743 w := len(buf) 744 print := false 745 for i := 0; i < prec; i++ { 746 digit := v % 10 747 print = print || digit != 0 748 if print { 749 w-- 750 buf[w] = byte(digit) + '0' 751 } 752 v /= 10 753 } 754 if print { 755 w-- 756 buf[w] = '.' 757 } 758 return w, v 759 } 760 761 // fmtInt formats v into the tail of buf. 762 // It returns the index where the output begins. 763 func fmtInt(buf []byte, v uint64) int { 764 w := len(buf) 765 if v == 0 { 766 w-- 767 buf[w] = '0' 768 } else { 769 for v > 0 { 770 w-- 771 buf[w] = byte(v%10) + '0' 772 v /= 10 773 } 774 } 775 return w 776 } 777 778 // Nanoseconds returns the duration as an integer nanosecond count. 779 func (d Duration) Nanoseconds() int64 { return int64(d) } 780 781 // Microseconds returns the duration as an integer microsecond count. 782 func (d Duration) Microseconds() int64 { return int64(d) / 1e3 } 783 784 // Milliseconds returns the duration as an integer millisecond count. 785 func (d Duration) Milliseconds() int64 { return int64(d) / 1e6 } 786 787 // These methods return float64 because the dominant 788 // use case is for printing a floating point number like 1.5s, and 789 // a truncation to integer would make them not useful in those cases. 790 // Splitting the integer and fraction ourselves guarantees that 791 // converting the returned float64 to an integer rounds the same 792 // way that a pure integer conversion would have, even in cases 793 // where, say, float64(d.Nanoseconds())/1e9 would have rounded 794 // differently. 795 796 // Seconds returns the duration as a floating point number of seconds. 797 func (d Duration) Seconds() float64 { 798 sec := d / Second 799 nsec := d % Second 800 return float64(sec) + float64(nsec)/1e9 801 } 802 803 // Minutes returns the duration as a floating point number of minutes. 804 func (d Duration) Minutes() float64 { 805 min := d / Minute 806 nsec := d % Minute 807 return float64(min) + float64(nsec)/(60*1e9) 808 } 809 810 // Hours returns the duration as a floating point number of hours. 811 func (d Duration) Hours() float64 { 812 hour := d / Hour 813 nsec := d % Hour 814 return float64(hour) + float64(nsec)/(60*60*1e9) 815 } 816 817 // Truncate returns the result of rounding d toward zero to a multiple of m. 818 // If m <= 0, Truncate returns d unchanged. 819 func (d Duration) Truncate(m Duration) Duration { 820 if m <= 0 { 821 return d 822 } 823 return d - d%m 824 } 825 826 // lessThanHalf reports whether x+x < y but avoids overflow, 827 // assuming x and y are both positive (Duration is signed). 828 func lessThanHalf(x, y Duration) bool { 829 return uint64(x)+uint64(x) < uint64(y) 830 } 831 832 // Round returns the result of rounding d to the nearest multiple of m. 833 // The rounding behavior for halfway values is to round away from zero. 834 // If the result exceeds the maximum (or minimum) 835 // value that can be stored in a [Duration], 836 // Round returns the maximum (or minimum) duration. 837 // If m <= 0, Round returns d unchanged. 838 func (d Duration) Round(m Duration) Duration { 839 if m <= 0 { 840 return d 841 } 842 r := d % m 843 if d < 0 { 844 r = -r 845 if lessThanHalf(r, m) { 846 return d + r 847 } 848 if d1 := d - m + r; d1 < d { 849 return d1 850 } 851 return minDuration // overflow 852 } 853 if lessThanHalf(r, m) { 854 return d - r 855 } 856 if d1 := d + m - r; d1 > d { 857 return d1 858 } 859 return maxDuration // overflow 860 } 861 862 // Abs returns the absolute value of d. 863 // As a special case, [math.MinInt64] is converted to [math.MaxInt64]. 864 func (d Duration) Abs() Duration { 865 switch { 866 case d >= 0: 867 return d 868 case d == minDuration: 869 return maxDuration 870 default: 871 return -d 872 } 873 } 874 875 // Add returns the time t+d. 876 func (t Time) Add(d Duration) Time { 877 dsec := int64(d / 1e9) 878 nsec := t.nsec() + int32(d%1e9) 879 if nsec >= 1e9 { 880 dsec++ 881 nsec -= 1e9 882 } else if nsec < 0 { 883 dsec-- 884 nsec += 1e9 885 } 886 t.wall = t.wall&^nsecMask | uint64(nsec) // update nsec 887 t.addSec(dsec) 888 if t.wall&hasMonotonic != 0 { 889 te := t.ext + int64(d) 890 if d < 0 && te > t.ext || d > 0 && te < t.ext { 891 // Monotonic clock reading now out of range; degrade to wall-only. 892 t.stripMono() 893 } else { 894 t.ext = te 895 } 896 } 897 return t 898 } 899 900 // Sub returns the duration t-u. If the result exceeds the maximum (or minimum) 901 // value that can be stored in a [Duration], the maximum (or minimum) duration 902 // will be returned. 903 // To compute t-d for a duration d, use t.Add(-d). 904 func (t Time) Sub(u Time) Duration { 905 if t.wall&u.wall&hasMonotonic != 0 { 906 return subMono(t.ext, u.ext) 907 } 908 d := Duration(t.sec()-u.sec())*Second + Duration(t.nsec()-u.nsec()) 909 // Check for overflow or underflow. 910 switch { 911 case u.Add(d).Equal(t): 912 return d // d is correct 913 case t.Before(u): 914 return minDuration // t - u is negative out of range 915 default: 916 return maxDuration // t - u is positive out of range 917 } 918 } 919 920 func subMono(t, u int64) Duration { 921 d := Duration(t - u) 922 if d < 0 && t > u { 923 return maxDuration // t - u is positive out of range 924 } 925 if d > 0 && t < u { 926 return minDuration // t - u is negative out of range 927 } 928 return d 929 } 930 931 // Since returns the time elapsed since t. 932 // It is shorthand for time.Now().Sub(t). 933 func Since(t Time) Duration { 934 if t.wall&hasMonotonic != 0 { 935 // Common case optimization: if t has monotonic time, then Sub will use only it. 936 return subMono(runtimeNano()-startNano, t.ext) 937 } 938 return Now().Sub(t) 939 } 940 941 // Until returns the duration until t. 942 // It is shorthand for t.Sub(time.Now()). 943 func Until(t Time) Duration { 944 if t.wall&hasMonotonic != 0 { 945 // Common case optimization: if t has monotonic time, then Sub will use only it. 946 return subMono(t.ext, runtimeNano()-startNano) 947 } 948 return t.Sub(Now()) 949 } 950 951 // AddDate returns the time corresponding to adding the 952 // given number of years, months, and days to t. 953 // For example, AddDate(-1, 2, 3) applied to January 1, 2011 954 // returns March 4, 2010. 955 // 956 // Note that dates are fundamentally coupled to timezones, and calendrical 957 // periods like days don't have fixed durations. AddDate uses the Location of 958 // the Time value to determine these durations. That means that the same 959 // AddDate arguments can produce a different shift in absolute time depending on 960 // the base Time value and its Location. For example, AddDate(0, 0, 1) applied 961 // to 12:00 on March 27 always returns 12:00 on March 28. At some locations and 962 // in some years this is a 24 hour shift. In others it's a 23 hour shift due to 963 // daylight savings time transitions. 964 // 965 // AddDate normalizes its result in the same way that Date does, 966 // so, for example, adding one month to October 31 yields 967 // December 1, the normalized form for November 31. 968 func (t Time) AddDate(years int, months int, days int) Time { 969 year, month, day := t.Date() 970 hour, min, sec := t.Clock() 971 return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec()), t.Location()) 972 } 973 974 const ( 975 secondsPerMinute = 60 976 secondsPerHour = 60 * secondsPerMinute 977 secondsPerDay = 24 * secondsPerHour 978 secondsPerWeek = 7 * secondsPerDay 979 daysPer400Years = 365*400 + 97 980 daysPer100Years = 365*100 + 24 981 daysPer4Years = 365*4 + 1 982 ) 983 984 // date computes the year, day of year, and when full=true, 985 // the month and day in which t occurs. 986 func (t Time) date(full bool) (year int, month Month, day int, yday int) { 987 return absDate(t.abs(), full) 988 } 989 990 // absDate is like date but operates on an absolute time. 991 func absDate(abs uint64, full bool) (year int, month Month, day int, yday int) { 992 // Split into time and day. 993 d := abs / secondsPerDay 994 995 // Account for 400 year cycles. 996 n := d / daysPer400Years 997 y := 400 * n 998 d -= daysPer400Years * n 999 1000 // Cut off 100-year cycles. 1001 // The last cycle has one extra leap year, so on the last day 1002 // of that year, day / daysPer100Years will be 4 instead of 3. 1003 // Cut it back down to 3 by subtracting n>>2. 1004 n = d / daysPer100Years 1005 n -= n >> 2 1006 y += 100 * n 1007 d -= daysPer100Years * n 1008 1009 // Cut off 4-year cycles. 1010 // The last cycle has a missing leap year, which does not 1011 // affect the computation. 1012 n = d / daysPer4Years 1013 y += 4 * n 1014 d -= daysPer4Years * n 1015 1016 // Cut off years within a 4-year cycle. 1017 // The last year is a leap year, so on the last day of that year, 1018 // day / 365 will be 4 instead of 3. Cut it back down to 3 1019 // by subtracting n>>2. 1020 n = d / 365 1021 n -= n >> 2 1022 y += n 1023 d -= 365 * n 1024 1025 year = int(int64(y) + absoluteZeroYear) 1026 yday = int(d) 1027 1028 if !full { 1029 return 1030 } 1031 1032 day = yday 1033 if isLeap(year) { 1034 // Leap year 1035 switch { 1036 case day > 31+29-1: 1037 // After leap day; pretend it wasn't there. 1038 day-- 1039 case day == 31+29-1: 1040 // Leap day. 1041 month = February 1042 day = 29 1043 return 1044 } 1045 } 1046 1047 // Estimate month on assumption that every month has 31 days. 1048 // The estimate may be too low by at most one month, so adjust. 1049 month = Month(day / 31) 1050 end := int(daysBefore[month+1]) 1051 var begin int 1052 if day >= end { 1053 month++ 1054 begin = end 1055 } else { 1056 begin = int(daysBefore[month]) 1057 } 1058 1059 month++ // because January is 1 1060 day = day - begin + 1 1061 return 1062 } 1063 1064 // daysBefore[m] counts the number of days in a non-leap year 1065 // before month m begins. There is an entry for m=12, counting 1066 // the number of days before January of next year (365). 1067 var daysBefore = [...]int32{ 1068 0, 1069 31, 1070 31 + 28, 1071 31 + 28 + 31, 1072 31 + 28 + 31 + 30, 1073 31 + 28 + 31 + 30 + 31, 1074 31 + 28 + 31 + 30 + 31 + 30, 1075 31 + 28 + 31 + 30 + 31 + 30 + 31, 1076 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31, 1077 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30, 1078 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31, 1079 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30, 1080 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31, 1081 } 1082 1083 func daysIn(m Month, year int) int { 1084 if m == February && isLeap(year) { 1085 return 29 1086 } 1087 return int(daysBefore[m] - daysBefore[m-1]) 1088 } 1089 1090 // daysSinceEpoch takes a year and returns the number of days from 1091 // the absolute epoch to the start of that year. 1092 // This is basically (year - zeroYear) * 365, but accounting for leap days. 1093 func daysSinceEpoch(year int) uint64 { 1094 y := uint64(int64(year) - absoluteZeroYear) 1095 1096 // Add in days from 400-year cycles. 1097 n := y / 400 1098 y -= 400 * n 1099 d := daysPer400Years * n 1100 1101 // Add in 100-year cycles. 1102 n = y / 100 1103 y -= 100 * n 1104 d += daysPer100Years * n 1105 1106 // Add in 4-year cycles. 1107 n = y / 4 1108 y -= 4 * n 1109 d += daysPer4Years * n 1110 1111 // Add in non-leap years. 1112 n = y 1113 d += 365 * n 1114 1115 return d 1116 } 1117 1118 // Provided by package runtime. 1119 func now() (sec int64, nsec int32, mono int64) 1120 1121 // runtimeNano returns the current value of the runtime clock in nanoseconds. 1122 // 1123 //go:linkname runtimeNano runtime.nanotime 1124 func runtimeNano() int64 1125 1126 // Monotonic times are reported as offsets from startNano. 1127 // We initialize startNano to runtimeNano() - 1 so that on systems where 1128 // monotonic time resolution is fairly low (e.g. Windows 2008 1129 // which appears to have a default resolution of 15ms), 1130 // we avoid ever reporting a monotonic time of 0. 1131 // (Callers may want to use 0 as "time not set".) 1132 var startNano int64 = runtimeNano() - 1 1133 1134 // Now returns the current local time. 1135 func Now() Time { 1136 sec, nsec, mono := now() 1137 mono -= startNano 1138 sec += unixToInternal - minWall 1139 if uint64(sec)>>33 != 0 { 1140 // Seconds field overflowed the 33 bits available when 1141 // storing a monotonic time. This will be true after 1142 // March 16, 2157. 1143 return Time{uint64(nsec), sec + minWall, Local} 1144 } 1145 return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local} 1146 } 1147 1148 func unixTime(sec int64, nsec int32) Time { 1149 return Time{uint64(nsec), sec + unixToInternal, Local} 1150 } 1151 1152 // UTC returns t with the location set to UTC. 1153 func (t Time) UTC() Time { 1154 t.setLoc(&utcLoc) 1155 return t 1156 } 1157 1158 // Local returns t with the location set to local time. 1159 func (t Time) Local() Time { 1160 t.setLoc(Local) 1161 return t 1162 } 1163 1164 // In returns a copy of t representing the same time instant, but 1165 // with the copy's location information set to loc for display 1166 // purposes. 1167 // 1168 // In panics if loc is nil. 1169 func (t Time) In(loc *Location) Time { 1170 if loc == nil { 1171 panic("time: missing Location in call to Time.In") 1172 } 1173 t.setLoc(loc) 1174 return t 1175 } 1176 1177 // Location returns the time zone information associated with t. 1178 func (t Time) Location() *Location { 1179 l := t.loc 1180 if l == nil { 1181 l = UTC 1182 } 1183 return l 1184 } 1185 1186 // Zone computes the time zone in effect at time t, returning the abbreviated 1187 // name of the zone (such as "CET") and its offset in seconds east of UTC. 1188 func (t Time) Zone() (name string, offset int) { 1189 name, offset, _, _, _ = t.loc.lookup(t.unixSec()) 1190 return 1191 } 1192 1193 // ZoneBounds returns the bounds of the time zone in effect at time t. 1194 // The zone begins at start and the next zone begins at end. 1195 // If the zone begins at the beginning of time, start will be returned as a zero Time. 1196 // If the zone goes on forever, end will be returned as a zero Time. 1197 // The Location of the returned times will be the same as t. 1198 func (t Time) ZoneBounds() (start, end Time) { 1199 _, _, startSec, endSec, _ := t.loc.lookup(t.unixSec()) 1200 if startSec != alpha { 1201 start = unixTime(startSec, 0) 1202 start.setLoc(t.loc) 1203 } 1204 if endSec != omega { 1205 end = unixTime(endSec, 0) 1206 end.setLoc(t.loc) 1207 } 1208 return 1209 } 1210 1211 // Unix returns t as a Unix time, the number of seconds elapsed 1212 // since January 1, 1970 UTC. The result does not depend on the 1213 // location associated with t. 1214 // Unix-like operating systems often record time as a 32-bit 1215 // count of seconds, but since the method here returns a 64-bit 1216 // value it is valid for billions of years into the past or future. 1217 func (t Time) Unix() int64 { 1218 return t.unixSec() 1219 } 1220 1221 // UnixMilli returns t as a Unix time, the number of milliseconds elapsed since 1222 // January 1, 1970 UTC. The result is undefined if the Unix time in 1223 // milliseconds cannot be represented by an int64 (a date more than 292 million 1224 // years before or after 1970). The result does not depend on the 1225 // location associated with t. 1226 func (t Time) UnixMilli() int64 { 1227 return t.unixSec()*1e3 + int64(t.nsec())/1e6 1228 } 1229 1230 // UnixMicro returns t as a Unix time, the number of microseconds elapsed since 1231 // January 1, 1970 UTC. The result is undefined if the Unix time in 1232 // microseconds cannot be represented by an int64 (a date before year -290307 or 1233 // after year 294246). The result does not depend on the location associated 1234 // with t. 1235 func (t Time) UnixMicro() int64 { 1236 return t.unixSec()*1e6 + int64(t.nsec())/1e3 1237 } 1238 1239 // UnixNano returns t as a Unix time, the number of nanoseconds elapsed 1240 // since January 1, 1970 UTC. The result is undefined if the Unix time 1241 // in nanoseconds cannot be represented by an int64 (a date before the year 1242 // 1678 or after 2262). Note that this means the result of calling UnixNano 1243 // on the zero Time is undefined. The result does not depend on the 1244 // location associated with t. 1245 func (t Time) UnixNano() int64 { 1246 return (t.unixSec())*1e9 + int64(t.nsec()) 1247 } 1248 1249 const ( 1250 timeBinaryVersionV1 byte = iota + 1 // For general situation 1251 timeBinaryVersionV2 // For LMT only 1252 ) 1253 1254 // MarshalBinary implements the encoding.BinaryMarshaler interface. 1255 func (t Time) MarshalBinary() ([]byte, error) { 1256 var offsetMin int16 // minutes east of UTC. -1 is UTC. 1257 var offsetSec int8 1258 version := timeBinaryVersionV1 1259 1260 if t.Location() == UTC { 1261 offsetMin = -1 1262 } else { 1263 _, offset := t.Zone() 1264 if offset%60 != 0 { 1265 version = timeBinaryVersionV2 1266 offsetSec = int8(offset % 60) 1267 } 1268 1269 offset /= 60 1270 if offset < -32768 || offset == -1 || offset > 32767 { 1271 return nil, errors.New("Time.MarshalBinary: unexpected zone offset") 1272 } 1273 offsetMin = int16(offset) 1274 } 1275 1276 sec := t.sec() 1277 nsec := t.nsec() 1278 enc := []byte{ 1279 version, // byte 0 : version 1280 byte(sec >> 56), // bytes 1-8: seconds 1281 byte(sec >> 48), 1282 byte(sec >> 40), 1283 byte(sec >> 32), 1284 byte(sec >> 24), 1285 byte(sec >> 16), 1286 byte(sec >> 8), 1287 byte(sec), 1288 byte(nsec >> 24), // bytes 9-12: nanoseconds 1289 byte(nsec >> 16), 1290 byte(nsec >> 8), 1291 byte(nsec), 1292 byte(offsetMin >> 8), // bytes 13-14: zone offset in minutes 1293 byte(offsetMin), 1294 } 1295 if version == timeBinaryVersionV2 { 1296 enc = append(enc, byte(offsetSec)) 1297 } 1298 1299 return enc, nil 1300 } 1301 1302 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. 1303 func (t *Time) UnmarshalBinary(data []byte) error { 1304 buf := data 1305 if len(buf) == 0 { 1306 return errors.New("Time.UnmarshalBinary: no data") 1307 } 1308 1309 version := buf[0] 1310 if version != timeBinaryVersionV1 && version != timeBinaryVersionV2 { 1311 return errors.New("Time.UnmarshalBinary: unsupported version") 1312 } 1313 1314 wantLen := /*version*/ 1 + /*sec*/ 8 + /*nsec*/ 4 + /*zone offset*/ 2 1315 if version == timeBinaryVersionV2 { 1316 wantLen++ 1317 } 1318 if len(buf) != wantLen { 1319 return errors.New("Time.UnmarshalBinary: invalid length") 1320 } 1321 1322 buf = buf[1:] 1323 sec := int64(buf[7]) | int64(buf[6])<<8 | int64(buf[5])<<16 | int64(buf[4])<<24 | 1324 int64(buf[3])<<32 | int64(buf[2])<<40 | int64(buf[1])<<48 | int64(buf[0])<<56 1325 1326 buf = buf[8:] 1327 nsec := int32(buf[3]) | int32(buf[2])<<8 | int32(buf[1])<<16 | int32(buf[0])<<24 1328 1329 buf = buf[4:] 1330 offset := int(int16(buf[1])|int16(buf[0])<<8) * 60 1331 if version == timeBinaryVersionV2 { 1332 offset += int(buf[2]) 1333 } 1334 1335 *t = Time{} 1336 t.wall = uint64(nsec) 1337 t.ext = sec 1338 1339 if offset == -1*60 { 1340 t.setLoc(&utcLoc) 1341 } else if _, localoff, _, _, _ := Local.lookup(t.unixSec()); offset == localoff { 1342 t.setLoc(Local) 1343 } else { 1344 t.setLoc(FixedZone("", offset)) 1345 } 1346 1347 return nil 1348 } 1349 1350 // TODO(rsc): Remove GobEncoder, GobDecoder, MarshalJSON, UnmarshalJSON in Go 2. 1351 // The same semantics will be provided by the generic MarshalBinary, MarshalText, 1352 // UnmarshalBinary, UnmarshalText. 1353 1354 // GobEncode implements the gob.GobEncoder interface. 1355 func (t Time) GobEncode() ([]byte, error) { 1356 return t.MarshalBinary() 1357 } 1358 1359 // GobDecode implements the gob.GobDecoder interface. 1360 func (t *Time) GobDecode(data []byte) error { 1361 return t.UnmarshalBinary(data) 1362 } 1363 1364 // MarshalJSON implements the [json.Marshaler] interface. 1365 // The time is a quoted string in the RFC 3339 format with sub-second precision. 1366 // If the timestamp cannot be represented as valid RFC 3339 1367 // (e.g., the year is out of range), then an error is reported. 1368 func (t Time) MarshalJSON() ([]byte, error) { 1369 b := make([]byte, 0, len(RFC3339Nano)+len(`""`)) 1370 b = append(b, '"') 1371 b, err := t.appendStrictRFC3339(b) 1372 b = append(b, '"') 1373 if err != nil { 1374 return nil, errors.New("Time.MarshalJSON: " + err.Error()) 1375 } 1376 return b, nil 1377 } 1378 1379 // UnmarshalJSON implements the [json.Unmarshaler] interface. 1380 // The time must be a quoted string in the RFC 3339 format. 1381 func (t *Time) UnmarshalJSON(data []byte) error { 1382 if string(data) == "null" { 1383 return nil 1384 } 1385 // TODO(https://go.dev/issue/47353): Properly unescape a JSON string. 1386 if len(data) < 2 || data[0] != '"' || data[len(data)-1] != '"' { 1387 return errors.New("Time.UnmarshalJSON: input is not a JSON string") 1388 } 1389 data = data[len(`"`) : len(data)-len(`"`)] 1390 var err error 1391 *t, err = parseStrictRFC3339(data) 1392 return err 1393 } 1394 1395 // MarshalText implements the [encoding.TextMarshaler] interface. 1396 // The time is formatted in RFC 3339 format with sub-second precision. 1397 // If the timestamp cannot be represented as valid RFC 3339 1398 // (e.g., the year is out of range), then an error is reported. 1399 func (t Time) MarshalText() ([]byte, error) { 1400 b := make([]byte, 0, len(RFC3339Nano)) 1401 b, err := t.appendStrictRFC3339(b) 1402 if err != nil { 1403 return nil, errors.New("Time.MarshalText: " + err.Error()) 1404 } 1405 return b, nil 1406 } 1407 1408 // UnmarshalText implements the [encoding.TextUnmarshaler] interface. 1409 // The time must be in the RFC 3339 format. 1410 func (t *Time) UnmarshalText(data []byte) error { 1411 var err error 1412 *t, err = parseStrictRFC3339(data) 1413 return err 1414 } 1415 1416 // Unix returns the local Time corresponding to the given Unix time, 1417 // sec seconds and nsec nanoseconds since January 1, 1970 UTC. 1418 // It is valid to pass nsec outside the range [0, 999999999]. 1419 // Not all sec values have a corresponding time value. One such 1420 // value is 1<<63-1 (the largest int64 value). 1421 func Unix(sec int64, nsec int64) Time { 1422 if nsec < 0 || nsec >= 1e9 { 1423 n := nsec / 1e9 1424 sec += n 1425 nsec -= n * 1e9 1426 if nsec < 0 { 1427 nsec += 1e9 1428 sec-- 1429 } 1430 } 1431 return unixTime(sec, int32(nsec)) 1432 } 1433 1434 // UnixMilli returns the local Time corresponding to the given Unix time, 1435 // msec milliseconds since January 1, 1970 UTC. 1436 func UnixMilli(msec int64) Time { 1437 return Unix(msec/1e3, (msec%1e3)*1e6) 1438 } 1439 1440 // UnixMicro returns the local Time corresponding to the given Unix time, 1441 // usec microseconds since January 1, 1970 UTC. 1442 func UnixMicro(usec int64) Time { 1443 return Unix(usec/1e6, (usec%1e6)*1e3) 1444 } 1445 1446 // IsDST reports whether the time in the configured location is in Daylight Savings Time. 1447 func (t Time) IsDST() bool { 1448 _, _, _, _, isDST := t.loc.lookup(t.Unix()) 1449 return isDST 1450 } 1451 1452 func isLeap(year int) bool { 1453 return year%4 == 0 && (year%100 != 0 || year%400 == 0) 1454 } 1455 1456 // norm returns nhi, nlo such that 1457 // 1458 // hi * base + lo == nhi * base + nlo 1459 // 0 <= nlo < base 1460 func norm(hi, lo, base int) (nhi, nlo int) { 1461 if lo < 0 { 1462 n := (-lo-1)/base + 1 1463 hi -= n 1464 lo += n * base 1465 } 1466 if lo >= base { 1467 n := lo / base 1468 hi += n 1469 lo -= n * base 1470 } 1471 return hi, lo 1472 } 1473 1474 // Date returns the Time corresponding to 1475 // 1476 // yyyy-mm-dd hh:mm:ss + nsec nanoseconds 1477 // 1478 // in the appropriate zone for that time in the given location. 1479 // 1480 // The month, day, hour, min, sec, and nsec values may be outside 1481 // their usual ranges and will be normalized during the conversion. 1482 // For example, October 32 converts to November 1. 1483 // 1484 // A daylight savings time transition skips or repeats times. 1485 // For example, in the United States, March 13, 2011 2:15am never occurred, 1486 // while November 6, 2011 1:15am occurred twice. In such cases, the 1487 // choice of time zone, and therefore the time, is not well-defined. 1488 // Date returns a time that is correct in one of the two zones involved 1489 // in the transition, but it does not guarantee which. 1490 // 1491 // Date panics if loc is nil. 1492 func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time { 1493 if loc == nil { 1494 panic("time: missing Location in call to Date") 1495 } 1496 1497 // Normalize month, overflowing into year. 1498 m := int(month) - 1 1499 year, m = norm(year, m, 12) 1500 month = Month(m) + 1 1501 1502 // Normalize nsec, sec, min, hour, overflowing into day. 1503 sec, nsec = norm(sec, nsec, 1e9) 1504 min, sec = norm(min, sec, 60) 1505 hour, min = norm(hour, min, 60) 1506 day, hour = norm(day, hour, 24) 1507 1508 // Compute days since the absolute epoch. 1509 d := daysSinceEpoch(year) 1510 1511 // Add in days before this month. 1512 d += uint64(daysBefore[month-1]) 1513 if isLeap(year) && month >= March { 1514 d++ // February 29 1515 } 1516 1517 // Add in days before today. 1518 d += uint64(day - 1) 1519 1520 // Add in time elapsed today. 1521 abs := d * secondsPerDay 1522 abs += uint64(hour*secondsPerHour + min*secondsPerMinute + sec) 1523 1524 unix := int64(abs) + (absoluteToInternal + internalToUnix) 1525 1526 // Look for zone offset for expected time, so we can adjust to UTC. 1527 // The lookup function expects UTC, so first we pass unix in the 1528 // hope that it will not be too close to a zone transition, 1529 // and then adjust if it is. 1530 _, offset, start, end, _ := loc.lookup(unix) 1531 if offset != 0 { 1532 utc := unix - int64(offset) 1533 // If utc is valid for the time zone we found, then we have the right offset. 1534 // If not, we get the correct offset by looking up utc in the location. 1535 if utc < start || utc >= end { 1536 _, offset, _, _, _ = loc.lookup(utc) 1537 } 1538 unix -= int64(offset) 1539 } 1540 1541 t := unixTime(unix, int32(nsec)) 1542 t.setLoc(loc) 1543 return t 1544 } 1545 1546 // Truncate returns the result of rounding t down to a multiple of d (since the zero time). 1547 // If d <= 0, Truncate returns t stripped of any monotonic clock reading but otherwise unchanged. 1548 // 1549 // Truncate operates on the time as an absolute duration since the 1550 // zero time; it does not operate on the presentation form of the 1551 // time. Thus, Truncate(Hour) may return a time with a non-zero 1552 // minute, depending on the time's Location. 1553 func (t Time) Truncate(d Duration) Time { 1554 t.stripMono() 1555 if d <= 0 { 1556 return t 1557 } 1558 _, r := div(t, d) 1559 return t.Add(-r) 1560 } 1561 1562 // Round returns the result of rounding t to the nearest multiple of d (since the zero time). 1563 // The rounding behavior for halfway values is to round up. 1564 // If d <= 0, Round returns t stripped of any monotonic clock reading but otherwise unchanged. 1565 // 1566 // Round operates on the time as an absolute duration since the 1567 // zero time; it does not operate on the presentation form of the 1568 // time. Thus, Round(Hour) may return a time with a non-zero 1569 // minute, depending on the time's Location. 1570 func (t Time) Round(d Duration) Time { 1571 t.stripMono() 1572 if d <= 0 { 1573 return t 1574 } 1575 _, r := div(t, d) 1576 if lessThanHalf(r, d) { 1577 return t.Add(-r) 1578 } 1579 return t.Add(d - r) 1580 } 1581 1582 // div divides t by d and returns the quotient parity and remainder. 1583 // We don't use the quotient parity anymore (round half up instead of round to even) 1584 // but it's still here in case we change our minds. 1585 func div(t Time, d Duration) (qmod2 int, r Duration) { 1586 neg := false 1587 nsec := t.nsec() 1588 sec := t.sec() 1589 if sec < 0 { 1590 // Operate on absolute value. 1591 neg = true 1592 sec = -sec 1593 nsec = -nsec 1594 if nsec < 0 { 1595 nsec += 1e9 1596 sec-- // sec >= 1 before the -- so safe 1597 } 1598 } 1599 1600 switch { 1601 // Special case: 2d divides 1 second. 1602 case d < Second && Second%(d+d) == 0: 1603 qmod2 = int(nsec/int32(d)) & 1 1604 r = Duration(nsec % int32(d)) 1605 1606 // Special case: d is a multiple of 1 second. 1607 case d%Second == 0: 1608 d1 := int64(d / Second) 1609 qmod2 = int(sec/d1) & 1 1610 r = Duration(sec%d1)*Second + Duration(nsec) 1611 1612 // General case. 1613 // This could be faster if more cleverness were applied, 1614 // but it's really only here to avoid special case restrictions in the API. 1615 // No one will care about these cases. 1616 default: 1617 // Compute nanoseconds as 128-bit number. 1618 sec := uint64(sec) 1619 tmp := (sec >> 32) * 1e9 1620 u1 := tmp >> 32 1621 u0 := tmp << 32 1622 tmp = (sec & 0xFFFFFFFF) * 1e9 1623 u0x, u0 := u0, u0+tmp 1624 if u0 < u0x { 1625 u1++ 1626 } 1627 u0x, u0 = u0, u0+uint64(nsec) 1628 if u0 < u0x { 1629 u1++ 1630 } 1631 1632 // Compute remainder by subtracting r<<k for decreasing k. 1633 // Quotient parity is whether we subtract on last round. 1634 d1 := uint64(d) 1635 for d1>>63 != 1 { 1636 d1 <<= 1 1637 } 1638 d0 := uint64(0) 1639 for { 1640 qmod2 = 0 1641 if u1 > d1 || u1 == d1 && u0 >= d0 { 1642 // subtract 1643 qmod2 = 1 1644 u0x, u0 = u0, u0-d0 1645 if u0 > u0x { 1646 u1-- 1647 } 1648 u1 -= d1 1649 } 1650 if d1 == 0 && d0 == uint64(d) { 1651 break 1652 } 1653 d0 >>= 1 1654 d0 |= (d1 & 1) << 63 1655 d1 >>= 1 1656 } 1657 r = Duration(u0) 1658 } 1659 1660 if neg && r != 0 { 1661 // If input was negative and not an exact multiple of d, we computed q, r such that 1662 // q*d + r = -t 1663 // But the right answers are given by -(q-1), d-r: 1664 // q*d + r = -t 1665 // -q*d - r = t 1666 // -(q-1)*d + (d - r) = t 1667 qmod2 ^= 1 1668 r = d - r 1669 } 1670 return 1671 } 1672