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