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 return t.sec() < u.sec() || t.sec() == u.sec() && t.nsec() < u.nsec() 256 } 257 258 // Equal reports whether t and u represent the same time instant. 259 // Two times can be equal even if they are in different locations. 260 // For example, 6:00 +0200 CEST and 4:00 UTC are Equal. 261 // See the documentation on the Time type for the pitfalls of using == with 262 // Time values; most code should use Equal instead. 263 func (t Time) Equal(u Time) bool { 264 if t.wall&u.wall&hasMonotonic != 0 { 265 return t.ext == u.ext 266 } 267 return t.sec() == u.sec() && t.nsec() == u.nsec() 268 } 269 270 // A Month specifies a month of the year (January = 1, ...). 271 type Month int 272 273 const ( 274 January Month = 1 + iota 275 February 276 March 277 April 278 May 279 June 280 July 281 August 282 September 283 October 284 November 285 December 286 ) 287 288 var months = [...]string{ 289 "January", 290 "February", 291 "March", 292 "April", 293 "May", 294 "June", 295 "July", 296 "August", 297 "September", 298 "October", 299 "November", 300 "December", 301 } 302 303 // String returns the English name of the month ("January", "February", ...). 304 func (m Month) String() string { 305 if January <= m && m <= December { 306 return months[m-1] 307 } 308 buf := make([]byte, 20) 309 n := fmtInt(buf, uint64(m)) 310 return "%!Month(" + string(buf[n:]) + ")" 311 } 312 313 // A Weekday specifies a day of the week (Sunday = 0, ...). 314 type Weekday int 315 316 const ( 317 Sunday Weekday = iota 318 Monday 319 Tuesday 320 Wednesday 321 Thursday 322 Friday 323 Saturday 324 ) 325 326 var days = [...]string{ 327 "Sunday", 328 "Monday", 329 "Tuesday", 330 "Wednesday", 331 "Thursday", 332 "Friday", 333 "Saturday", 334 } 335 336 // String returns the English name of the day ("Sunday", "Monday", ...). 337 func (d Weekday) String() string { 338 if Sunday <= d && d <= Saturday { 339 return days[d] 340 } 341 buf := make([]byte, 20) 342 n := fmtInt(buf, uint64(d)) 343 return "%!Weekday(" + string(buf[n:]) + ")" 344 } 345 346 // Computations on time. 347 // 348 // The zero value for a Time is defined to be 349 // January 1, year 1, 00:00:00.000000000 UTC 350 // which (1) looks like a zero, or as close as you can get in a date 351 // (1-1-1 00:00:00 UTC), (2) is unlikely enough to arise in practice to 352 // be a suitable "not set" sentinel, unlike Jan 1 1970, and (3) has a 353 // non-negative year even in time zones west of UTC, unlike 1-1-0 354 // 00:00:00 UTC, which would be 12-31-(-1) 19:00:00 in New York. 355 // 356 // The zero Time value does not force a specific epoch for the time 357 // representation. For example, to use the Unix epoch internally, we 358 // could define that to distinguish a zero value from Jan 1 1970, that 359 // time would be represented by sec=-1, nsec=1e9. However, it does 360 // suggest a representation, namely using 1-1-1 00:00:00 UTC as the 361 // epoch, and that's what we do. 362 // 363 // The Add and Sub computations are oblivious to the choice of epoch. 364 // 365 // The presentation computations - year, month, minute, and so on - all 366 // rely heavily on division and modulus by positive constants. For 367 // calendrical calculations we want these divisions to round down, even 368 // for negative values, so that the remainder is always positive, but 369 // Go's division (like most hardware division instructions) rounds to 370 // zero. We can still do those computations and then adjust the result 371 // for a negative numerator, but it's annoying to write the adjustment 372 // over and over. Instead, we can change to a different epoch so long 373 // ago that all the times we care about will be positive, and then round 374 // to zero and round down coincide. These presentation routines already 375 // have to add the zone offset, so adding the translation to the 376 // alternate epoch is cheap. For example, having a non-negative time t 377 // means that we can write 378 // 379 // sec = t % 60 380 // 381 // instead of 382 // 383 // sec = t % 60 384 // if sec < 0 { 385 // sec += 60 386 // } 387 // 388 // everywhere. 389 // 390 // The calendar runs on an exact 400 year cycle: a 400-year calendar 391 // printed for 1970-2369 will apply as well to 2370-2769. Even the days 392 // of the week match up. It simplifies the computations to choose the 393 // cycle boundaries so that the exceptional years are always delayed as 394 // long as possible. That means choosing a year equal to 1 mod 400, so 395 // that the first leap year is the 4th year, the first missed leap year 396 // is the 100th year, and the missed missed leap year is the 400th year. 397 // So we'd prefer instead to print a calendar for 2001-2400 and reuse it 398 // for 2401-2800. 399 // 400 // Finally, it's convenient if the delta between the Unix epoch and 401 // long-ago epoch is representable by an int64 constant. 402 // 403 // These three considerations—choose an epoch as early as possible, that 404 // uses a year equal to 1 mod 400, and that is no more than 2⁶³ seconds 405 // earlier than 1970—bring us to the year -292277022399. We refer to 406 // this year as the absolute zero year, and to times measured as a uint64 407 // seconds since this year as absolute times. 408 // 409 // Times measured as an int64 seconds since the year 1—the representation 410 // used for Time's sec field—are called internal times. 411 // 412 // Times measured as an int64 seconds since the year 1970 are called Unix 413 // times. 414 // 415 // It is tempting to just use the year 1 as the absolute epoch, defining 416 // that the routines are only valid for years >= 1. However, the 417 // routines would then be invalid when displaying the epoch in time zones 418 // west of UTC, since it is year 0. It doesn't seem tenable to say that 419 // printing the zero time correctly isn't supported in half the time 420 // zones. By comparison, it's reasonable to mishandle some times in 421 // the year -292277022399. 422 // 423 // All this is opaque to clients of the API and can be changed if a 424 // better implementation presents itself. 425 426 const ( 427 // The unsigned zero year for internal calculations. 428 // Must be 1 mod 400, and times before it will not compute correctly, 429 // but otherwise can be changed at will. 430 absoluteZeroYear = -292277022399 431 432 // The year of the zero Time. 433 // Assumed by the unixToInternal computation below. 434 internalYear = 1 435 436 // Offsets to convert between internal and absolute or Unix times. 437 absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay 438 internalToAbsolute = -absoluteToInternal 439 440 unixToInternal int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay 441 internalToUnix int64 = -unixToInternal 442 443 wallToInternal int64 = (1884*365 + 1884/4 - 1884/100 + 1884/400) * secondsPerDay 444 internalToWall int64 = -wallToInternal 445 ) 446 447 // IsZero reports whether t represents the zero time instant, 448 // January 1, year 1, 00:00:00 UTC. 449 func (t Time) IsZero() bool { 450 return t.sec() == 0 && t.nsec() == 0 451 } 452 453 // abs returns the time t as an absolute time, adjusted by the zone offset. 454 // It is called when computing a presentation property like Month or Hour. 455 func (t Time) abs() uint64 { 456 l := t.loc 457 // Avoid function calls when possible. 458 if l == nil || l == &localLoc { 459 l = l.get() 460 } 461 sec := t.unixSec() 462 if l != &utcLoc { 463 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 464 sec += int64(l.cacheZone.offset) 465 } else { 466 _, offset, _, _ := l.lookup(sec) 467 sec += int64(offset) 468 } 469 } 470 return uint64(sec + (unixToInternal + internalToAbsolute)) 471 } 472 473 // locabs is a combination of the Zone and abs methods, 474 // extracting both return values from a single zone lookup. 475 func (t Time) locabs() (name string, offset int, abs uint64) { 476 l := t.loc 477 if l == nil || l == &localLoc { 478 l = l.get() 479 } 480 // Avoid function call if we hit the local time cache. 481 sec := t.unixSec() 482 if l != &utcLoc { 483 if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { 484 name = l.cacheZone.name 485 offset = l.cacheZone.offset 486 } else { 487 name, offset, _, _ = l.lookup(sec) 488 } 489 sec += int64(offset) 490 } else { 491 name = "UTC" 492 } 493 abs = uint64(sec + (unixToInternal + internalToAbsolute)) 494 return 495 } 496 497 // Date returns the year, month, and day in which t occurs. 498 func (t Time) Date() (year int, month Month, day int) { 499 year, month, day, _ = t.date(true) 500 return 501 } 502 503 // Year returns the year in which t occurs. 504 func (t Time) Year() int { 505 year, _, _, _ := t.date(false) 506 return year 507 } 508 509 // Month returns the month of the year specified by t. 510 func (t Time) Month() Month { 511 _, month, _, _ := t.date(true) 512 return month 513 } 514 515 // Day returns the day of the month specified by t. 516 func (t Time) Day() int { 517 _, _, day, _ := t.date(true) 518 return day 519 } 520 521 // Weekday returns the day of the week specified by t. 522 func (t Time) Weekday() Weekday { 523 return absWeekday(t.abs()) 524 } 525 526 // absWeekday is like Weekday but operates on an absolute time. 527 func absWeekday(abs uint64) Weekday { 528 // January 1 of the absolute year, like January 1 of 2001, was a Monday. 529 sec := (abs + uint64(Monday)*secondsPerDay) % secondsPerWeek 530 return Weekday(int(sec) / secondsPerDay) 531 } 532 533 // ISOWeek returns the ISO 8601 year and week number in which t occurs. 534 // Week ranges from 1 to 53. Jan 01 to Jan 03 of year n might belong to 535 // week 52 or 53 of year n-1, and Dec 29 to Dec 31 might belong to week 1 536 // of year n+1. 537 func (t Time) ISOWeek() (year, week int) { 538 year, month, day, yday := t.date(true) 539 wday := int(t.Weekday()+6) % 7 // weekday but Monday = 0. 540 const ( 541 Mon int = iota 542 Tue 543 Wed 544 Thu 545 Fri 546 Sat 547 Sun 548 ) 549 550 // Calculate week as number of Mondays in year up to 551 // and including today, plus 1 because the first week is week 0. 552 // Putting the + 1 inside the numerator as a + 7 keeps the 553 // numerator from being negative, which would cause it to 554 // round incorrectly. 555 week = (yday - wday + 7) / 7 556 557 // The week number is now correct under the assumption 558 // that the first Monday of the year is in week 1. 559 // If Jan 1 is a Tuesday, Wednesday, or Thursday, the first Monday 560 // is actually in week 2. 561 jan1wday := (wday - yday + 7*53) % 7 562 if Tue <= jan1wday && jan1wday <= Thu { 563 week++ 564 } 565 566 // If the week number is still 0, we're in early January but in 567 // the last week of last year. 568 if week == 0 { 569 year-- 570 week = 52 571 // A year has 53 weeks when Jan 1 or Dec 31 is a Thursday, 572 // meaning Jan 1 of the next year is a Friday 573 // or it was a leap year and Jan 1 of the next year is a Saturday. 574 if jan1wday == Fri || (jan1wday == Sat && isLeap(year)) { 575 week++ 576 } 577 } 578 579 // December 29 to 31 are in week 1 of next year if 580 // they are after the last Thursday of the year and 581 // December 31 is a Monday, Tuesday, or Wednesday. 582 if month == December && day >= 29 && wday < Thu { 583 if dec31wday := (wday + 31 - day) % 7; Mon <= dec31wday && dec31wday <= Wed { 584 year++ 585 week = 1 586 } 587 } 588 589 return 590 } 591 592 // Clock returns the hour, minute, and second within the day specified by t. 593 func (t Time) Clock() (hour, min, sec int) { 594 return absClock(t.abs()) 595 } 596 597 // absClock is like clock but operates on an absolute time. 598 func absClock(abs uint64) (hour, min, sec int) { 599 sec = int(abs % secondsPerDay) 600 hour = sec / secondsPerHour 601 sec -= hour * secondsPerHour 602 min = sec / secondsPerMinute 603 sec -= min * secondsPerMinute 604 return 605 } 606 607 // Hour returns the hour within the day specified by t, in the range [0, 23]. 608 func (t Time) Hour() int { 609 return int(t.abs()%secondsPerDay) / secondsPerHour 610 } 611 612 // Minute returns the minute offset within the hour specified by t, in the range [0, 59]. 613 func (t Time) Minute() int { 614 return int(t.abs()%secondsPerHour) / secondsPerMinute 615 } 616 617 // Second returns the second offset within the minute specified by t, in the range [0, 59]. 618 func (t Time) Second() int { 619 return int(t.abs() % secondsPerMinute) 620 } 621 622 // Nanosecond returns the nanosecond offset within the second specified by t, 623 // in the range [0, 999999999]. 624 func (t Time) Nanosecond() int { 625 return int(t.nsec()) 626 } 627 628 // YearDay returns the day of the year specified by t, in the range [1,365] for non-leap years, 629 // and [1,366] in leap years. 630 func (t Time) YearDay() int { 631 _, _, _, yday := t.date(false) 632 return yday + 1 633 } 634 635 // A Duration represents the elapsed time between two instants 636 // as an int64 nanosecond count. The representation limits the 637 // largest representable duration to approximately 290 years. 638 type Duration int64 639 640 const ( 641 minDuration Duration = -1 << 63 642 maxDuration Duration = 1<<63 - 1 643 ) 644 645 // Common durations. There is no definition for units of Day or larger 646 // to avoid confusion across daylight savings time zone transitions. 647 // 648 // To count the number of units in a Duration, divide: 649 // second := time.Second 650 // fmt.Print(int64(second/time.Millisecond)) // prints 1000 651 // 652 // To convert an integer number of units to a Duration, multiply: 653 // seconds := 10 654 // fmt.Print(time.Duration(seconds)*time.Second) // prints 10s 655 // 656 const ( 657 Nanosecond Duration = 1 658 Microsecond = 1000 * Nanosecond 659 Millisecond = 1000 * Microsecond 660 Second = 1000 * Millisecond 661 Minute = 60 * Second 662 Hour = 60 * Minute 663 ) 664 665 // String returns a string representing the duration in the form "72h3m0.5s". 666 // Leading zero units are omitted. As a special case, durations less than one 667 // second format use a smaller unit (milli-, micro-, or nanoseconds) to ensure 668 // that the leading digit is non-zero. The zero duration formats as 0s. 669 func (d Duration) String() string { 670 // Largest time is 2540400h10m10.000000000s 671 var buf [32]byte 672 w := len(buf) 673 674 u := uint64(d) 675 neg := d < 0 676 if neg { 677 u = -u 678 } 679 680 if u < uint64(Second) { 681 // Special case: if duration is smaller than a second, 682 // use smaller units, like 1.2ms 683 var prec int 684 w-- 685 buf[w] = 's' 686 w-- 687 switch { 688 case u == 0: 689 return "0s" 690 case u < uint64(Microsecond): 691 // print nanoseconds 692 prec = 0 693 buf[w] = 'n' 694 case u < uint64(Millisecond): 695 // print microseconds 696 prec = 3 697 // U+00B5 'µ' micro sign == 0xC2 0xB5 698 w-- // Need room for two bytes. 699 copy(buf[w:], "µ") 700 default: 701 // print milliseconds 702 prec = 6 703 buf[w] = 'm' 704 } 705 w, u = fmtFrac(buf[:w], u, prec) 706 w = fmtInt(buf[:w], u) 707 } else { 708 w-- 709 buf[w] = 's' 710 711 w, u = fmtFrac(buf[:w], u, 9) 712 713 // u is now integer seconds 714 w = fmtInt(buf[:w], u%60) 715 u /= 60 716 717 // u is now integer minutes 718 if u > 0 { 719 w-- 720 buf[w] = 'm' 721 w = fmtInt(buf[:w], u%60) 722 u /= 60 723 724 // u is now integer hours 725 // Stop at hours because days can be different lengths. 726 if u > 0 { 727 w-- 728 buf[w] = 'h' 729 w = fmtInt(buf[:w], u) 730 } 731 } 732 } 733 734 if neg { 735 w-- 736 buf[w] = '-' 737 } 738 739 return string(buf[w:]) 740 } 741 742 // fmtFrac formats the fraction of v/10**prec (e.g., ".12345") into the 743 // tail of buf, omitting trailing zeros. It omits the decimal 744 // point too when the fraction is 0. It returns the index where the 745 // output bytes begin and the value v/10**prec. 746 func fmtFrac(buf []byte, v uint64, prec int) (nw int, nv uint64) { 747 // Omit trailing zeros up to and including decimal point. 748 w := len(buf) 749 print := false 750 for i := 0; i < prec; i++ { 751 digit := v % 10 752 print = print || digit != 0 753 if print { 754 w-- 755 buf[w] = byte(digit) + '0' 756 } 757 v /= 10 758 } 759 if print { 760 w-- 761 buf[w] = '.' 762 } 763 return w, v 764 } 765 766 // fmtInt formats v into the tail of buf. 767 // It returns the index where the output begins. 768 func fmtInt(buf []byte, v uint64) int { 769 w := len(buf) 770 if v == 0 { 771 w-- 772 buf[w] = '0' 773 } else { 774 for v > 0 { 775 w-- 776 buf[w] = byte(v%10) + '0' 777 v /= 10 778 } 779 } 780 return w 781 } 782 783 // Nanoseconds returns the duration as an integer nanosecond count. 784 func (d Duration) Nanoseconds() int64 { return int64(d) } 785 786 // These methods return float64 because the dominant 787 // use case is for printing a floating point number like 1.5s, and 788 // a truncation to integer would make them not useful in those cases. 789 // Splitting the integer and fraction ourselves guarantees that 790 // converting the returned float64 to an integer rounds the same 791 // way that a pure integer conversion would have, even in cases 792 // where, say, float64(d.Nanoseconds())/1e9 would have rounded 793 // differently. 794 795 // Seconds returns the duration as a floating point number of seconds. 796 func (d Duration) Seconds() float64 { 797 sec := d / Second 798 nsec := d % Second 799 return float64(sec) + float64(nsec)/1e9 800 } 801 802 // Minutes returns the duration as a floating point number of minutes. 803 func (d Duration) Minutes() float64 { 804 min := d / Minute 805 nsec := d % Minute 806 return float64(min) + float64(nsec)/(60*1e9) 807 } 808 809 // Hours returns the duration as a floating point number of hours. 810 func (d Duration) Hours() float64 { 811 hour := d / Hour 812 nsec := d % Hour 813 return float64(hour) + float64(nsec)/(60*60*1e9) 814 } 815 816 // Truncate returns the result of rounding d toward zero to a multiple of m. 817 // If m <= 0, Truncate returns d unchanged. 818 func (d Duration) Truncate(m Duration) Duration { 819 if m <= 0 { 820 return d 821 } 822 return d - d%m 823 } 824 825 // lessThanHalf reports whether x+x < y but avoids overflow, 826 // assuming x and y are both positive (Duration is signed). 827 func lessThanHalf(x, y Duration) bool { 828 return uint64(x)+uint64(x) < uint64(y) 829 } 830 831 // Round returns the result of rounding d to the nearest multiple of m. 832 // The rounding behavior for halfway values is to round away from zero. 833 // If the result exceeds the maximum (or minimum) 834 // value that can be stored in a Duration, 835 // Round returns the maximum (or minimum) duration. 836 // If m <= 0, Round returns d unchanged. 837 func (d Duration) Round(m Duration) Duration { 838 if m <= 0 { 839 return d 840 } 841 r := d % m 842 if d < 0 { 843 r = -r 844 if lessThanHalf(r, m) { 845 return d + r 846 } 847 if d1 := d - m + r; d1 < d { 848 return d1 849 } 850 return minDuration // overflow 851 } 852 if lessThanHalf(r, m) { 853 return d - r 854 } 855 if d1 := d + m - r; d1 > d { 856 return d1 857 } 858 return maxDuration // overflow 859 } 860 861 // Add returns the time t+d. 862 func (t Time) Add(d Duration) Time { 863 dsec := int64(d / 1e9) 864 nsec := t.nsec() + int32(d%1e9) 865 if nsec >= 1e9 { 866 dsec++ 867 nsec -= 1e9 868 } else if nsec < 0 { 869 dsec-- 870 nsec += 1e9 871 } 872 t.wall = t.wall&^nsecMask | uint64(nsec) // update nsec 873 t.addSec(dsec) 874 if t.wall&hasMonotonic != 0 { 875 te := t.ext + int64(d) 876 if d < 0 && te > t.ext || d > 0 && te < t.ext { 877 // Monotonic clock reading now out of range; degrade to wall-only. 878 t.stripMono() 879 } else { 880 t.ext = te 881 } 882 } 883 return t 884 } 885 886 // Sub returns the duration t-u. If the result exceeds the maximum (or minimum) 887 // value that can be stored in a Duration, the maximum (or minimum) duration 888 // will be returned. 889 // To compute t-d for a duration d, use t.Add(-d). 890 func (t Time) Sub(u Time) Duration { 891 if t.wall&u.wall&hasMonotonic != 0 { 892 te := t.ext 893 ue := u.ext 894 d := Duration(te - ue) 895 if d < 0 && te > ue { 896 return maxDuration // t - u is positive out of range 897 } 898 if d > 0 && te < ue { 899 return minDuration // t - u is negative out of range 900 } 901 return d 902 } 903 d := Duration(t.sec()-u.sec())*Second + Duration(t.nsec()-u.nsec()) 904 // Check for overflow or underflow. 905 switch { 906 case u.Add(d).Equal(t): 907 return d // d is correct 908 case t.Before(u): 909 return minDuration // t - u is negative out of range 910 default: 911 return maxDuration // t - u is positive out of range 912 } 913 } 914 915 // Since returns the time elapsed since t. 916 // It is shorthand for time.Now().Sub(t). 917 func Since(t Time) Duration { 918 var now Time 919 if t.wall&hasMonotonic != 0 { 920 // Common case optimization: if t has monotomic time, then Sub will use only it. 921 now = Time{hasMonotonic, runtimeNano() - startNano, nil} 922 } else { 923 now = Now() 924 } 925 return now.Sub(t) 926 } 927 928 // Until returns the duration until t. 929 // It is shorthand for t.Sub(time.Now()). 930 func Until(t Time) Duration { 931 var now Time 932 if t.wall&hasMonotonic != 0 { 933 // Common case optimization: if t has monotomic time, then Sub will use only it. 934 now = Time{hasMonotonic, runtimeNano() - startNano, nil} 935 } else { 936 now = Now() 937 } 938 return t.Sub(now) 939 } 940 941 // AddDate returns the time corresponding to adding the 942 // given number of years, months, and days to t. 943 // For example, AddDate(-1, 2, 3) applied to January 1, 2011 944 // returns March 4, 2010. 945 // 946 // AddDate normalizes its result in the same way that Date does, 947 // so, for example, adding one month to October 31 yields 948 // December 1, the normalized form for November 31. 949 func (t Time) AddDate(years int, months int, days int) Time { 950 year, month, day := t.Date() 951 hour, min, sec := t.Clock() 952 return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec()), t.Location()) 953 } 954 955 const ( 956 secondsPerMinute = 60 957 secondsPerHour = 60 * secondsPerMinute 958 secondsPerDay = 24 * secondsPerHour 959 secondsPerWeek = 7 * secondsPerDay 960 daysPer400Years = 365*400 + 97 961 daysPer100Years = 365*100 + 24 962 daysPer4Years = 365*4 + 1 963 ) 964 965 // date computes the year, day of year, and when full=true, 966 // the month and day in which t occurs. 967 func (t Time) date(full bool) (year int, month Month, day int, yday int) { 968 return absDate(t.abs(), full) 969 } 970 971 // absDate is like date but operates on an absolute time. 972 func absDate(abs uint64, full bool) (year int, month Month, day int, yday int) { 973 // Split into time and day. 974 d := abs / secondsPerDay 975 976 // Account for 400 year cycles. 977 n := d / daysPer400Years 978 y := 400 * n 979 d -= daysPer400Years * n 980 981 // Cut off 100-year cycles. 982 // The last cycle has one extra leap year, so on the last day 983 // of that year, day / daysPer100Years will be 4 instead of 3. 984 // Cut it back down to 3 by subtracting n>>2. 985 n = d / daysPer100Years 986 n -= n >> 2 987 y += 100 * n 988 d -= daysPer100Years * n 989 990 // Cut off 4-year cycles. 991 // The last cycle has a missing leap year, which does not 992 // affect the computation. 993 n = d / daysPer4Years 994 y += 4 * n 995 d -= daysPer4Years * n 996 997 // Cut off years within a 4-year cycle. 998 // The last year is a leap year, so on the last day of that year, 999 // day / 365 will be 4 instead of 3. Cut it back down to 3 1000 // by subtracting n>>2. 1001 n = d / 365 1002 n -= n >> 2 1003 y += n 1004 d -= 365 * n 1005 1006 year = int(int64(y) + absoluteZeroYear) 1007 yday = int(d) 1008 1009 if !full { 1010 return 1011 } 1012 1013 day = yday 1014 if isLeap(year) { 1015 // Leap year 1016 switch { 1017 case day > 31+29-1: 1018 // After leap day; pretend it wasn't there. 1019 day-- 1020 case day == 31+29-1: 1021 // Leap day. 1022 month = February 1023 day = 29 1024 return 1025 } 1026 } 1027 1028 // Estimate month on assumption that every month has 31 days. 1029 // The estimate may be too low by at most one month, so adjust. 1030 month = Month(day / 31) 1031 end := int(daysBefore[month+1]) 1032 var begin int 1033 if day >= end { 1034 month++ 1035 begin = end 1036 } else { 1037 begin = int(daysBefore[month]) 1038 } 1039 1040 month++ // because January is 1 1041 day = day - begin + 1 1042 return 1043 } 1044 1045 // daysBefore[m] counts the number of days in a non-leap year 1046 // before month m begins. There is an entry for m=12, counting 1047 // the number of days before January of next year (365). 1048 var daysBefore = [...]int32{ 1049 0, 1050 31, 1051 31 + 28, 1052 31 + 28 + 31, 1053 31 + 28 + 31 + 30, 1054 31 + 28 + 31 + 30 + 31, 1055 31 + 28 + 31 + 30 + 31 + 30, 1056 31 + 28 + 31 + 30 + 31 + 30 + 31, 1057 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31, 1058 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30, 1059 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31, 1060 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30, 1061 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31, 1062 } 1063 1064 func daysIn(m Month, year int) int { 1065 if m == February && isLeap(year) { 1066 return 29 1067 } 1068 return int(daysBefore[m] - daysBefore[m-1]) 1069 } 1070 1071 // Provided by package runtime. 1072 func now() (sec int64, nsec int32, mono int64) 1073 1074 // runtimeNano returns the current value of the runtime clock in nanoseconds. 1075 //go:linkname runtimeNano runtime.nanotime 1076 func runtimeNano() int64 1077 1078 // Monotonic times are reported as offsets from startNano. 1079 // We initialize startNano to runtimeNano() - 1 so that on systems where 1080 // monotonic time resolution is fairly low (e.g. Windows 2008 1081 // which appears to have a default resolution of 15ms), 1082 // we avoid ever reporting a monotonic time of 0. 1083 // (Callers may want to use 0 as "time not set".) 1084 var startNano int64 = runtimeNano() - 1 1085 1086 // Now returns the current local time. 1087 func Now() Time { 1088 sec, nsec, mono := now() 1089 mono -= startNano 1090 sec += unixToInternal - minWall 1091 if uint64(sec)>>33 != 0 { 1092 return Time{uint64(nsec), sec + minWall, Local} 1093 } 1094 return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local} 1095 } 1096 1097 func unixTime(sec int64, nsec int32) Time { 1098 return Time{uint64(nsec), sec + unixToInternal, Local} 1099 } 1100 1101 // UTC returns t with the location set to UTC. 1102 func (t Time) UTC() Time { 1103 t.setLoc(&utcLoc) 1104 return t 1105 } 1106 1107 // Local returns t with the location set to local time. 1108 func (t Time) Local() Time { 1109 t.setLoc(Local) 1110 return t 1111 } 1112 1113 // In returns a copy of t representing the same time instant, but 1114 // with the copy's location information set to loc for display 1115 // purposes. 1116 // 1117 // In panics if loc is nil. 1118 func (t Time) In(loc *Location) Time { 1119 if loc == nil { 1120 panic("time: missing Location in call to Time.In") 1121 } 1122 t.setLoc(loc) 1123 return t 1124 } 1125 1126 // Location returns the time zone information associated with t. 1127 func (t Time) Location() *Location { 1128 l := t.loc 1129 if l == nil { 1130 l = UTC 1131 } 1132 return l 1133 } 1134 1135 // Zone computes the time zone in effect at time t, returning the abbreviated 1136 // name of the zone (such as "CET") and its offset in seconds east of UTC. 1137 func (t Time) Zone() (name string, offset int) { 1138 name, offset, _, _ = t.loc.lookup(t.unixSec()) 1139 return 1140 } 1141 1142 // Unix returns t as a Unix time, the number of seconds elapsed 1143 // since January 1, 1970 UTC. The result does not depend on the 1144 // location associated with t. 1145 func (t Time) Unix() int64 { 1146 return t.unixSec() 1147 } 1148 1149 // UnixNano returns t as a Unix time, the number of nanoseconds elapsed 1150 // since January 1, 1970 UTC. The result is undefined if the Unix time 1151 // in nanoseconds cannot be represented by an int64 (a date before the year 1152 // 1678 or after 2262). Note that this means the result of calling UnixNano 1153 // on the zero Time is undefined. The result does not depend on the 1154 // location associated with t. 1155 func (t Time) UnixNano() int64 { 1156 return (t.unixSec())*1e9 + int64(t.nsec()) 1157 } 1158 1159 const timeBinaryVersion byte = 1 1160 1161 // MarshalBinary implements the encoding.BinaryMarshaler interface. 1162 func (t Time) MarshalBinary() ([]byte, error) { 1163 var offsetMin int16 // minutes east of UTC. -1 is UTC. 1164 1165 if t.Location() == UTC { 1166 offsetMin = -1 1167 } else { 1168 _, offset := t.Zone() 1169 if offset%60 != 0 { 1170 return nil, errors.New("Time.MarshalBinary: zone offset has fractional minute") 1171 } 1172 offset /= 60 1173 if offset < -32768 || offset == -1 || offset > 32767 { 1174 return nil, errors.New("Time.MarshalBinary: unexpected zone offset") 1175 } 1176 offsetMin = int16(offset) 1177 } 1178 1179 sec := t.sec() 1180 nsec := t.nsec() 1181 enc := []byte{ 1182 timeBinaryVersion, // byte 0 : version 1183 byte(sec >> 56), // bytes 1-8: seconds 1184 byte(sec >> 48), 1185 byte(sec >> 40), 1186 byte(sec >> 32), 1187 byte(sec >> 24), 1188 byte(sec >> 16), 1189 byte(sec >> 8), 1190 byte(sec), 1191 byte(nsec >> 24), // bytes 9-12: nanoseconds 1192 byte(nsec >> 16), 1193 byte(nsec >> 8), 1194 byte(nsec), 1195 byte(offsetMin >> 8), // bytes 13-14: zone offset in minutes 1196 byte(offsetMin), 1197 } 1198 1199 return enc, nil 1200 } 1201 1202 // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. 1203 func (t *Time) UnmarshalBinary(data []byte) error { 1204 buf := data 1205 if len(buf) == 0 { 1206 return errors.New("Time.UnmarshalBinary: no data") 1207 } 1208 1209 if buf[0] != timeBinaryVersion { 1210 return errors.New("Time.UnmarshalBinary: unsupported version") 1211 } 1212 1213 if len(buf) != /*version*/ 1+ /*sec*/ 8+ /*nsec*/ 4+ /*zone offset*/ 2 { 1214 return errors.New("Time.UnmarshalBinary: invalid length") 1215 } 1216 1217 buf = buf[1:] 1218 sec := int64(buf[7]) | int64(buf[6])<<8 | int64(buf[5])<<16 | int64(buf[4])<<24 | 1219 int64(buf[3])<<32 | int64(buf[2])<<40 | int64(buf[1])<<48 | int64(buf[0])<<56 1220 1221 buf = buf[8:] 1222 nsec := int32(buf[3]) | int32(buf[2])<<8 | int32(buf[1])<<16 | int32(buf[0])<<24 1223 1224 buf = buf[4:] 1225 offset := int(int16(buf[1])|int16(buf[0])<<8) * 60 1226 1227 *t = Time{} 1228 t.wall = uint64(nsec) 1229 t.ext = sec 1230 1231 if offset == -1*60 { 1232 t.setLoc(&utcLoc) 1233 } else if _, localoff, _, _ := Local.lookup(t.unixSec()); offset == localoff { 1234 t.setLoc(Local) 1235 } else { 1236 t.setLoc(FixedZone("", offset)) 1237 } 1238 1239 return nil 1240 } 1241 1242 // TODO(rsc): Remove GobEncoder, GobDecoder, MarshalJSON, UnmarshalJSON in Go 2. 1243 // The same semantics will be provided by the generic MarshalBinary, MarshalText, 1244 // UnmarshalBinary, UnmarshalText. 1245 1246 // GobEncode implements the gob.GobEncoder interface. 1247 func (t Time) GobEncode() ([]byte, error) { 1248 return t.MarshalBinary() 1249 } 1250 1251 // GobDecode implements the gob.GobDecoder interface. 1252 func (t *Time) GobDecode(data []byte) error { 1253 return t.UnmarshalBinary(data) 1254 } 1255 1256 // MarshalJSON implements the json.Marshaler interface. 1257 // The time is a quoted string in RFC 3339 format, with sub-second precision added if present. 1258 func (t Time) MarshalJSON() ([]byte, error) { 1259 if y := t.Year(); y < 0 || y >= 10000 { 1260 // RFC 3339 is clear that years are 4 digits exactly. 1261 // See golang.org/issue/4556#c15 for more discussion. 1262 return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]") 1263 } 1264 1265 b := make([]byte, 0, len(RFC3339Nano)+2) 1266 b = append(b, '"') 1267 b = t.AppendFormat(b, RFC3339Nano) 1268 b = append(b, '"') 1269 return b, nil 1270 } 1271 1272 // UnmarshalJSON implements the json.Unmarshaler interface. 1273 // The time is expected to be a quoted string in RFC 3339 format. 1274 func (t *Time) UnmarshalJSON(data []byte) error { 1275 // Ignore null, like in the main JSON package. 1276 if string(data) == "null" { 1277 return nil 1278 } 1279 // Fractional seconds are handled implicitly by Parse. 1280 var err error 1281 *t, err = Parse(`"`+RFC3339+`"`, string(data)) 1282 return err 1283 } 1284 1285 // MarshalText implements the encoding.TextMarshaler interface. 1286 // The time is formatted in RFC 3339 format, with sub-second precision added if present. 1287 func (t Time) MarshalText() ([]byte, error) { 1288 if y := t.Year(); y < 0 || y >= 10000 { 1289 return nil, errors.New("Time.MarshalText: year outside of range [0,9999]") 1290 } 1291 1292 b := make([]byte, 0, len(RFC3339Nano)) 1293 return t.AppendFormat(b, RFC3339Nano), nil 1294 } 1295 1296 // UnmarshalText implements the encoding.TextUnmarshaler interface. 1297 // The time is expected to be in RFC 3339 format. 1298 func (t *Time) UnmarshalText(data []byte) error { 1299 // Fractional seconds are handled implicitly by Parse. 1300 var err error 1301 *t, err = Parse(RFC3339, string(data)) 1302 return err 1303 } 1304 1305 // Unix returns the local Time corresponding to the given Unix time, 1306 // sec seconds and nsec nanoseconds since January 1, 1970 UTC. 1307 // It is valid to pass nsec outside the range [0, 999999999]. 1308 // Not all sec values have a corresponding time value. One such 1309 // value is 1<<63-1 (the largest int64 value). 1310 func Unix(sec int64, nsec int64) Time { 1311 if nsec < 0 || nsec >= 1e9 { 1312 n := nsec / 1e9 1313 sec += n 1314 nsec -= n * 1e9 1315 if nsec < 0 { 1316 nsec += 1e9 1317 sec-- 1318 } 1319 } 1320 return unixTime(sec, int32(nsec)) 1321 } 1322 1323 func isLeap(year int) bool { 1324 return year%4 == 0 && (year%100 != 0 || year%400 == 0) 1325 } 1326 1327 // norm returns nhi, nlo such that 1328 // hi * base + lo == nhi * base + nlo 1329 // 0 <= nlo < base 1330 func norm(hi, lo, base int) (nhi, nlo int) { 1331 if lo < 0 { 1332 n := (-lo-1)/base + 1 1333 hi -= n 1334 lo += n * base 1335 } 1336 if lo >= base { 1337 n := lo / base 1338 hi += n 1339 lo -= n * base 1340 } 1341 return hi, lo 1342 } 1343 1344 // Date returns the Time corresponding to 1345 // yyyy-mm-dd hh:mm:ss + nsec nanoseconds 1346 // in the appropriate zone for that time in the given location. 1347 // 1348 // The month, day, hour, min, sec, and nsec values may be outside 1349 // their usual ranges and will be normalized during the conversion. 1350 // For example, October 32 converts to November 1. 1351 // 1352 // A daylight savings time transition skips or repeats times. 1353 // For example, in the United States, March 13, 2011 2:15am never occurred, 1354 // while November 6, 2011 1:15am occurred twice. In such cases, the 1355 // choice of time zone, and therefore the time, is not well-defined. 1356 // Date returns a time that is correct in one of the two zones involved 1357 // in the transition, but it does not guarantee which. 1358 // 1359 // Date panics if loc is nil. 1360 func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time { 1361 if loc == nil { 1362 panic("time: missing Location in call to Date") 1363 } 1364 1365 // Normalize month, overflowing into year. 1366 m := int(month) - 1 1367 year, m = norm(year, m, 12) 1368 month = Month(m) + 1 1369 1370 // Normalize nsec, sec, min, hour, overflowing into day. 1371 sec, nsec = norm(sec, nsec, 1e9) 1372 min, sec = norm(min, sec, 60) 1373 hour, min = norm(hour, min, 60) 1374 day, hour = norm(day, hour, 24) 1375 1376 y := uint64(int64(year) - absoluteZeroYear) 1377 1378 // Compute days since the absolute epoch. 1379 1380 // Add in days from 400-year cycles. 1381 n := y / 400 1382 y -= 400 * n 1383 d := daysPer400Years * n 1384 1385 // Add in 100-year cycles. 1386 n = y / 100 1387 y -= 100 * n 1388 d += daysPer100Years * n 1389 1390 // Add in 4-year cycles. 1391 n = y / 4 1392 y -= 4 * n 1393 d += daysPer4Years * n 1394 1395 // Add in non-leap years. 1396 n = y 1397 d += 365 * n 1398 1399 // Add in days before this month. 1400 d += uint64(daysBefore[month-1]) 1401 if isLeap(year) && month >= March { 1402 d++ // February 29 1403 } 1404 1405 // Add in days before today. 1406 d += uint64(day - 1) 1407 1408 // Add in time elapsed today. 1409 abs := d * secondsPerDay 1410 abs += uint64(hour*secondsPerHour + min*secondsPerMinute + sec) 1411 1412 unix := int64(abs) + (absoluteToInternal + internalToUnix) 1413 1414 // Look for zone offset for t, so we can adjust to UTC. 1415 // The lookup function expects UTC, so we pass t in the 1416 // hope that it will not be too close to a zone transition, 1417 // and then adjust if it is. 1418 _, offset, start, end := loc.lookup(unix) 1419 if offset != 0 { 1420 switch utc := unix - int64(offset); { 1421 case utc < start: 1422 _, offset, _, _ = loc.lookup(start - 1) 1423 case utc >= end: 1424 _, offset, _, _ = loc.lookup(end) 1425 } 1426 unix -= int64(offset) 1427 } 1428 1429 t := unixTime(unix, int32(nsec)) 1430 t.setLoc(loc) 1431 return t 1432 } 1433 1434 // Truncate returns the result of rounding t down to a multiple of d (since the zero time). 1435 // If d <= 0, Truncate returns t stripped of any monotonic clock reading but otherwise unchanged. 1436 // 1437 // Truncate operates on the time as an absolute duration since the 1438 // zero time; it does not operate on the presentation form of the 1439 // time. Thus, Truncate(Hour) may return a time with a non-zero 1440 // minute, depending on the time's Location. 1441 func (t Time) Truncate(d Duration) Time { 1442 t.stripMono() 1443 if d <= 0 { 1444 return t 1445 } 1446 _, r := div(t, d) 1447 return t.Add(-r) 1448 } 1449 1450 // Round returns the result of rounding t to the nearest multiple of d (since the zero time). 1451 // The rounding behavior for halfway values is to round up. 1452 // If d <= 0, Round returns t stripped of any monotonic clock reading but otherwise unchanged. 1453 // 1454 // Round operates on the time as an absolute duration since the 1455 // zero time; it does not operate on the presentation form of the 1456 // time. Thus, Round(Hour) may return a time with a non-zero 1457 // minute, depending on the time's Location. 1458 func (t Time) Round(d Duration) Time { 1459 t.stripMono() 1460 if d <= 0 { 1461 return t 1462 } 1463 _, r := div(t, d) 1464 if lessThanHalf(r, d) { 1465 return t.Add(-r) 1466 } 1467 return t.Add(d - r) 1468 } 1469 1470 // div divides t by d and returns the quotient parity and remainder. 1471 // We don't use the quotient parity anymore (round half up instead of round to even) 1472 // but it's still here in case we change our minds. 1473 func div(t Time, d Duration) (qmod2 int, r Duration) { 1474 neg := false 1475 nsec := t.nsec() 1476 sec := t.sec() 1477 if sec < 0 { 1478 // Operate on absolute value. 1479 neg = true 1480 sec = -sec 1481 nsec = -nsec 1482 if nsec < 0 { 1483 nsec += 1e9 1484 sec-- // sec >= 1 before the -- so safe 1485 } 1486 } 1487 1488 switch { 1489 // Special case: 2d divides 1 second. 1490 case d < Second && Second%(d+d) == 0: 1491 qmod2 = int(nsec/int32(d)) & 1 1492 r = Duration(nsec % int32(d)) 1493 1494 // Special case: d is a multiple of 1 second. 1495 case d%Second == 0: 1496 d1 := int64(d / Second) 1497 qmod2 = int(sec/d1) & 1 1498 r = Duration(sec%d1)*Second + Duration(nsec) 1499 1500 // General case. 1501 // This could be faster if more cleverness were applied, 1502 // but it's really only here to avoid special case restrictions in the API. 1503 // No one will care about these cases. 1504 default: 1505 // Compute nanoseconds as 128-bit number. 1506 sec := uint64(sec) 1507 tmp := (sec >> 32) * 1e9 1508 u1 := tmp >> 32 1509 u0 := tmp << 32 1510 tmp = (sec & 0xFFFFFFFF) * 1e9 1511 u0x, u0 := u0, u0+tmp 1512 if u0 < u0x { 1513 u1++ 1514 } 1515 u0x, u0 = u0, u0+uint64(nsec) 1516 if u0 < u0x { 1517 u1++ 1518 } 1519 1520 // Compute remainder by subtracting r<<k for decreasing k. 1521 // Quotient parity is whether we subtract on last round. 1522 d1 := uint64(d) 1523 for d1>>63 != 1 { 1524 d1 <<= 1 1525 } 1526 d0 := uint64(0) 1527 for { 1528 qmod2 = 0 1529 if u1 > d1 || u1 == d1 && u0 >= d0 { 1530 // subtract 1531 qmod2 = 1 1532 u0x, u0 = u0, u0-d0 1533 if u0 > u0x { 1534 u1-- 1535 } 1536 u1 -= d1 1537 } 1538 if d1 == 0 && d0 == uint64(d) { 1539 break 1540 } 1541 d0 >>= 1 1542 d0 |= (d1 & 1) << 63 1543 d1 >>= 1 1544 } 1545 r = Duration(u0) 1546 } 1547 1548 if neg && r != 0 { 1549 // If input was negative and not an exact multiple of d, we computed q, r such that 1550 // q*d + r = -t 1551 // But the right answers are given by -(q-1), d-r: 1552 // q*d + r = -t 1553 // -q*d - r = t 1554 // -(q-1)*d + (d - r) = t 1555 qmod2 ^= 1 1556 r = d - r 1557 } 1558 return 1559 } 1560