// Copyright 2009 The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. // Package time provides functionality for measuring and displaying time. // // The calendrical calculations always assume a Gregorian calendar, with // no leap seconds. // // Monotonic Clocks // // Operating systems provide both a “wall clock,” which is subject to // changes for clock synchronization, and a “monotonic clock,” which is // not. The general rule is that the wall clock is for telling time and // the monotonic clock is for measuring time. Rather than split the API, // in this package the Time returned by time.Now contains both a wall // clock reading and a monotonic clock reading; later time-telling // operations use the wall clock reading, but later time-measuring // operations, specifically comparisons and subtractions, use the // monotonic clock reading. // // For example, this code always computes a positive elapsed time of // approximately 20 milliseconds, even if the wall clock is changed during // the operation being timed: // // start := time.Now() // ... operation that takes 20 milliseconds ... // t := time.Now() // elapsed := t.Sub(start) // // Other idioms, such as time.Since(start), time.Until(deadline), and // time.Now().Before(deadline), are similarly robust against wall clock // resets. // // The rest of this section gives the precise details of how operations // use monotonic clocks, but understanding those details is not required // to use this package. // // The Time returned by time.Now contains a monotonic clock reading. // If Time t has a monotonic clock reading, t.Add adds the same duration to // both the wall clock and monotonic clock readings to compute the result. // Because t.AddDate(y, m, d), t.Round(d), and t.Truncate(d) are wall time // computations, they always strip any monotonic clock reading from their results. // Because t.In, t.Local, and t.UTC are used for their effect on the interpretation // of the wall time, they also strip any monotonic clock reading from their results. // The canonical way to strip a monotonic clock reading is to use t = t.Round(0). // // If Times t and u both contain monotonic clock readings, the operations // t.After(u), t.Before(u), t.Equal(u), and t.Sub(u) are carried out // using the monotonic clock readings alone, ignoring the wall clock // readings. If either t or u contains no monotonic clock reading, these // operations fall back to using the wall clock readings. // // On some systems the monotonic clock will stop if the computer goes to sleep. // On such a system, t.Sub(u) may not accurately reflect the actual // time that passed between t and u. // // Because the monotonic clock reading has no meaning outside // the current process, the serialized forms generated by t.GobEncode, // t.MarshalBinary, t.MarshalJSON, and t.MarshalText omit the monotonic // clock reading, and t.Format provides no format for it. Similarly, the // constructors time.Date, time.Parse, time.ParseInLocation, and time.Unix, // as well as the unmarshalers t.GobDecode, t.UnmarshalBinary. // t.UnmarshalJSON, and t.UnmarshalText always create times with // no monotonic clock reading. // // Note that the Go == operator compares not just the time instant but // also the Location and the monotonic clock reading. See the // documentation for the Time type for a discussion of equality // testing for Time values. // // For debugging, the result of t.String does include the monotonic // clock reading if present. If t != u because of different monotonic clock readings, // that difference will be visible when printing t.String() and u.String(). // package time import "errors" // A Time represents an instant in time with nanosecond precision. // // Programs using times should typically store and pass them as values, // not pointers. That is, time variables and struct fields should be of // type time.Time, not *time.Time. // // A Time value can be used by multiple goroutines simultaneously except // that the methods GobDecode, UnmarshalBinary, UnmarshalJSON and // UnmarshalText are not concurrency-safe. // // Time instants can be compared using the Before, After, and Equal methods. // The Sub method subtracts two instants, producing a Duration. // The Add method adds a Time and a Duration, producing a Time. // // The zero value of type Time is January 1, year 1, 00:00:00.000000000 UTC. // As this time is unlikely to come up in practice, the IsZero method gives // a simple way of detecting a time that has not been initialized explicitly. // // Each Time has associated with it a Location, consulted when computing the // presentation form of the time, such as in the Format, Hour, and Year methods. // The methods Local, UTC, and In return a Time with a specific location. // Changing the location in this way changes only the presentation; it does not // change the instant in time being denoted and therefore does not affect the // computations described in earlier paragraphs. // // In addition to the required “wall clock” reading, a Time may contain an optional // reading of the current process's monotonic clock, to provide additional precision // for comparison or subtraction. // See the “Monotonic Clocks” section in the package documentation for details. // // Note that the Go == operator compares not just the time instant but also the // Location and the monotonic clock reading. Therefore, Time values should not // be used as map or database keys without first guaranteeing that the // identical Location has been set for all values, which can be achieved // through use of the UTC or Local method, and that the monotonic clock reading // has been stripped by setting t = t.Round(0). In general, prefer t.Equal(u) // to t == u, since t.Equal uses the most accurate comparison available and // correctly handles the case when only one of its arguments has a monotonic // clock reading. // type Time struct { // wall and ext encode the wall time seconds, wall time nanoseconds, // and optional monotonic clock reading in nanoseconds. // // From high to low bit position, wall encodes a 1-bit flag (hasMonotonic), // a 33-bit seconds field, and a 30-bit wall time nanoseconds field. // The nanoseconds field is in the range [0, 999999999]. // If the hasMonotonic bit is 0, then the 33-bit field must be zero // and the full signed 64-bit wall seconds since Jan 1 year 1 is stored in ext. // If the hasMonotonic bit is 1, then the 33-bit field holds a 33-bit // unsigned wall seconds since Jan 1 year 1885, and ext holds a // signed 64-bit monotonic clock reading, nanoseconds since process start. wall uint64 ext int64 // loc specifies the Location that should be used to // determine the minute, hour, month, day, and year // that correspond to this Time. // The nil location means UTC. // All UTC times are represented with loc==nil, never loc==&utcLoc. loc *Location } const ( hasMonotonic = 1 << 63 maxWall = wallToInternal + (1<<33 - 1) // year 2157 minWall = wallToInternal // year 1885 nsecMask = 1<<30 - 1 nsecShift = 30 ) // These helpers for manipulating the wall and monotonic clock readings // take pointer receivers, even when they don't modify the time, // to make them cheaper to call. // nsec returns the time's nanoseconds. func (t *Time) nsec() int32 { return int32(t.wall & nsecMask) } // sec returns the time's seconds since Jan 1 year 1. func (t *Time) sec() int64 { if t.wall&hasMonotonic != 0 { return wallToInternal + int64(t.wall<<1>>(nsecShift+1)) } return t.ext } // unixSec returns the time's seconds since Jan 1 1970 (Unix time). func (t *Time) unixSec() int64 { return t.sec() + internalToUnix } // addSec adds d seconds to the time. func (t *Time) addSec(d int64) { if t.wall&hasMonotonic != 0 { sec := int64(t.wall << 1 >> (nsecShift + 1)) dsec := sec + d if 0 <= dsec && dsec <= 1<<33-1 { t.wall = t.wall&nsecMask | uint64(dsec)<<nsecShift | hasMonotonic return } // Wall second now out of range for packed field. // Move to ext. t.stripMono() } // TODO: Check for overflow. t.ext += d } // setLoc sets the location associated with the time. func (t *Time) setLoc(loc *Location) { if loc == &utcLoc { loc = nil } t.stripMono() t.loc = loc } // stripMono strips the monotonic clock reading in t. func (t *Time) stripMono() { if t.wall&hasMonotonic != 0 { t.ext = t.sec() t.wall &= nsecMask } } // setMono sets the monotonic clock reading in t. // If t cannot hold a monotonic clock reading, // because its wall time is too large, // setMono is a no-op. func (t *Time) setMono(m int64) { if t.wall&hasMonotonic == 0 { sec := t.ext if sec < minWall || maxWall < sec { return } t.wall |= hasMonotonic | uint64(sec-minWall)<<nsecShift } t.ext = m } // mono returns t's monotonic clock reading. // It returns 0 for a missing reading. // This function is used only for testing, // so it's OK that technically 0 is a valid // monotonic clock reading as well. func (t *Time) mono() int64 { if t.wall&hasMonotonic == 0 { return 0 } return t.ext } // After reports whether the time instant t is after u. func (t Time) After(u Time) bool { if t.wall&u.wall&hasMonotonic != 0 { return t.ext > u.ext } ts := t.sec() us := u.sec() return ts > us || ts == us && t.nsec() > u.nsec() } // Before reports whether the time instant t is before u. func (t Time) Before(u Time) bool { if t.wall&u.wall&hasMonotonic != 0 { return t.ext < u.ext } return t.sec() < u.sec() || t.sec() == u.sec() && t.nsec() < u.nsec() } // Equal reports whether t and u represent the same time instant. // Two times can be equal even if they are in different locations. // For example, 6:00 +0200 CEST and 4:00 UTC are Equal. // See the documentation on the Time type for the pitfalls of using == with // Time values; most code should use Equal instead. func (t Time) Equal(u Time) bool { if t.wall&u.wall&hasMonotonic != 0 { return t.ext == u.ext } return t.sec() == u.sec() && t.nsec() == u.nsec() } // A Month specifies a month of the year (January = 1, ...). type Month int const ( January Month = 1 + iota February March April May June July August September October November December ) var months = [...]string{ "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December", } // String returns the English name of the month ("January", "February", ...). func (m Month) String() string { if January <= m && m <= December { return months[m-1] } buf := make([]byte, 20) n := fmtInt(buf, uint64(m)) return "%!Month(" + string(buf[n:]) + ")" } // A Weekday specifies a day of the week (Sunday = 0, ...). type Weekday int const ( Sunday Weekday = iota Monday Tuesday Wednesday Thursday Friday Saturday ) var days = [...]string{ "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", } // String returns the English name of the day ("Sunday", "Monday", ...). func (d Weekday) String() string { if Sunday <= d && d <= Saturday { return days[d] } buf := make([]byte, 20) n := fmtInt(buf, uint64(d)) return "%!Weekday(" + string(buf[n:]) + ")" } // Computations on time. // // The zero value for a Time is defined to be // January 1, year 1, 00:00:00.000000000 UTC // which (1) looks like a zero, or as close as you can get in a date // (1-1-1 00:00:00 UTC), (2) is unlikely enough to arise in practice to // be a suitable "not set" sentinel, unlike Jan 1 1970, and (3) has a // non-negative year even in time zones west of UTC, unlike 1-1-0 // 00:00:00 UTC, which would be 12-31-(-1) 19:00:00 in New York. // // The zero Time value does not force a specific epoch for the time // representation. For example, to use the Unix epoch internally, we // could define that to distinguish a zero value from Jan 1 1970, that // time would be represented by sec=-1, nsec=1e9. However, it does // suggest a representation, namely using 1-1-1 00:00:00 UTC as the // epoch, and that's what we do. // // The Add and Sub computations are oblivious to the choice of epoch. // // The presentation computations - year, month, minute, and so on - all // rely heavily on division and modulus by positive constants. For // calendrical calculations we want these divisions to round down, even // for negative values, so that the remainder is always positive, but // Go's division (like most hardware division instructions) rounds to // zero. We can still do those computations and then adjust the result // for a negative numerator, but it's annoying to write the adjustment // over and over. Instead, we can change to a different epoch so long // ago that all the times we care about will be positive, and then round // to zero and round down coincide. These presentation routines already // have to add the zone offset, so adding the translation to the // alternate epoch is cheap. For example, having a non-negative time t // means that we can write // // sec = t % 60 // // instead of // // sec = t % 60 // if sec < 0 { // sec += 60 // } // // everywhere. // // The calendar runs on an exact 400 year cycle: a 400-year calendar // printed for 1970-2369 will apply as well to 2370-2769. Even the days // of the week match up. It simplifies the computations to choose the // cycle boundaries so that the exceptional years are always delayed as // long as possible. That means choosing a year equal to 1 mod 400, so // that the first leap year is the 4th year, the first missed leap year // is the 100th year, and the missed missed leap year is the 400th year. // So we'd prefer instead to print a calendar for 2001-2400 and reuse it // for 2401-2800. // // Finally, it's convenient if the delta between the Unix epoch and // long-ago epoch is representable by an int64 constant. // // These three considerations—choose an epoch as early as possible, that // uses a year equal to 1 mod 400, and that is no more than 2⁶³ seconds // earlier than 1970—bring us to the year -292277022399. We refer to // this year as the absolute zero year, and to times measured as a uint64 // seconds since this year as absolute times. // // Times measured as an int64 seconds since the year 1—the representation // used for Time's sec field—are called internal times. // // Times measured as an int64 seconds since the year 1970 are called Unix // times. // // It is tempting to just use the year 1 as the absolute epoch, defining // that the routines are only valid for years >= 1. However, the // routines would then be invalid when displaying the epoch in time zones // west of UTC, since it is year 0. It doesn't seem tenable to say that // printing the zero time correctly isn't supported in half the time // zones. By comparison, it's reasonable to mishandle some times in // the year -292277022399. // // All this is opaque to clients of the API and can be changed if a // better implementation presents itself. const ( // The unsigned zero year for internal calculations. // Must be 1 mod 400, and times before it will not compute correctly, // but otherwise can be changed at will. absoluteZeroYear = -292277022399 // The year of the zero Time. // Assumed by the unixToInternal computation below. internalYear = 1 // Offsets to convert between internal and absolute or Unix times. absoluteToInternal int64 = (absoluteZeroYear - internalYear) * 365.2425 * secondsPerDay internalToAbsolute = -absoluteToInternal unixToInternal int64 = (1969*365 + 1969/4 - 1969/100 + 1969/400) * secondsPerDay internalToUnix int64 = -unixToInternal wallToInternal int64 = (1884*365 + 1884/4 - 1884/100 + 1884/400) * secondsPerDay internalToWall int64 = -wallToInternal ) // IsZero reports whether t represents the zero time instant, // January 1, year 1, 00:00:00 UTC. func (t Time) IsZero() bool { return t.sec() == 0 && t.nsec() == 0 } // abs returns the time t as an absolute time, adjusted by the zone offset. // It is called when computing a presentation property like Month or Hour. func (t Time) abs() uint64 { l := t.loc // Avoid function calls when possible. if l == nil || l == &localLoc { l = l.get() } sec := t.unixSec() if l != &utcLoc { if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { sec += int64(l.cacheZone.offset) } else { _, offset, _, _ := l.lookup(sec) sec += int64(offset) } } return uint64(sec + (unixToInternal + internalToAbsolute)) } // locabs is a combination of the Zone and abs methods, // extracting both return values from a single zone lookup. func (t Time) locabs() (name string, offset int, abs uint64) { l := t.loc if l == nil || l == &localLoc { l = l.get() } // Avoid function call if we hit the local time cache. sec := t.unixSec() if l != &utcLoc { if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd { name = l.cacheZone.name offset = l.cacheZone.offset } else { name, offset, _, _ = l.lookup(sec) } sec += int64(offset) } else { name = "UTC" } abs = uint64(sec + (unixToInternal + internalToAbsolute)) return } // Date returns the year, month, and day in which t occurs. func (t Time) Date() (year int, month Month, day int) { year, month, day, _ = t.date(true) return } // Year returns the year in which t occurs. func (t Time) Year() int { year, _, _, _ := t.date(false) return year } // Month returns the month of the year specified by t. func (t Time) Month() Month { _, month, _, _ := t.date(true) return month } // Day returns the day of the month specified by t. func (t Time) Day() int { _, _, day, _ := t.date(true) return day } // Weekday returns the day of the week specified by t. func (t Time) Weekday() Weekday { return absWeekday(t.abs()) } // absWeekday is like Weekday but operates on an absolute time. func absWeekday(abs uint64) Weekday { // January 1 of the absolute year, like January 1 of 2001, was a Monday. sec := (abs + uint64(Monday)*secondsPerDay) % secondsPerWeek return Weekday(int(sec) / secondsPerDay) } // ISOWeek returns the ISO 8601 year and week number in which t occurs. // Week ranges from 1 to 53. Jan 01 to Jan 03 of year n might belong to // week 52 or 53 of year n-1, and Dec 29 to Dec 31 might belong to week 1 // of year n+1. func (t Time) ISOWeek() (year, week int) { year, month, day, yday := t.date(true) wday := int(t.Weekday()+6) % 7 // weekday but Monday = 0. const ( Mon int = iota Tue Wed Thu Fri Sat Sun ) // Calculate week as number of Mondays in year up to // and including today, plus 1 because the first week is week 0. // Putting the + 1 inside the numerator as a + 7 keeps the // numerator from being negative, which would cause it to // round incorrectly. week = (yday - wday + 7) / 7 // The week number is now correct under the assumption // that the first Monday of the year is in week 1. // If Jan 1 is a Tuesday, Wednesday, or Thursday, the first Monday // is actually in week 2. jan1wday := (wday - yday + 7*53) % 7 if Tue <= jan1wday && jan1wday <= Thu { week++ } // If the week number is still 0, we're in early January but in // the last week of last year. if week == 0 { year-- week = 52 // A year has 53 weeks when Jan 1 or Dec 31 is a Thursday, // meaning Jan 1 of the next year is a Friday // or it was a leap year and Jan 1 of the next year is a Saturday. if jan1wday == Fri || (jan1wday == Sat && isLeap(year)) { week++ } } // December 29 to 31 are in week 1 of next year if // they are after the last Thursday of the year and // December 31 is a Monday, Tuesday, or Wednesday. if month == December && day >= 29 && wday < Thu { if dec31wday := (wday + 31 - day) % 7; Mon <= dec31wday && dec31wday <= Wed { year++ week = 1 } } return } // Clock returns the hour, minute, and second within the day specified by t. func (t Time) Clock() (hour, min, sec int) { return absClock(t.abs()) } // absClock is like clock but operates on an absolute time. func absClock(abs uint64) (hour, min, sec int) { sec = int(abs % secondsPerDay) hour = sec / secondsPerHour sec -= hour * secondsPerHour min = sec / secondsPerMinute sec -= min * secondsPerMinute return } // Hour returns the hour within the day specified by t, in the range [0, 23]. func (t Time) Hour() int { return int(t.abs()%secondsPerDay) / secondsPerHour } // Minute returns the minute offset within the hour specified by t, in the range [0, 59]. func (t Time) Minute() int { return int(t.abs()%secondsPerHour) / secondsPerMinute } // Second returns the second offset within the minute specified by t, in the range [0, 59]. func (t Time) Second() int { return int(t.abs() % secondsPerMinute) } // Nanosecond returns the nanosecond offset within the second specified by t, // in the range [0, 999999999]. func (t Time) Nanosecond() int { return int(t.nsec()) } // YearDay returns the day of the year specified by t, in the range [1,365] for non-leap years, // and [1,366] in leap years. func (t Time) YearDay() int { _, _, _, yday := t.date(false) return yday + 1 } // A Duration represents the elapsed time between two instants // as an int64 nanosecond count. The representation limits the // largest representable duration to approximately 290 years. type Duration int64 const ( minDuration Duration = -1 << 63 maxDuration Duration = 1<<63 - 1 ) // Common durations. There is no definition for units of Day or larger // to avoid confusion across daylight savings time zone transitions. // // To count the number of units in a Duration, divide: // second := time.Second // fmt.Print(int64(second/time.Millisecond)) // prints 1000 // // To convert an integer number of units to a Duration, multiply: // seconds := 10 // fmt.Print(time.Duration(seconds)*time.Second) // prints 10s // const ( Nanosecond Duration = 1 Microsecond = 1000 * Nanosecond Millisecond = 1000 * Microsecond Second = 1000 * Millisecond Minute = 60 * Second Hour = 60 * Minute ) // String returns a string representing the duration in the form "72h3m0.5s". // Leading zero units are omitted. As a special case, durations less than one // second format use a smaller unit (milli-, micro-, or nanoseconds) to ensure // that the leading digit is non-zero. The zero duration formats as 0s. func (d Duration) String() string { // Largest time is 2540400h10m10.000000000s var buf [32]byte w := len(buf) u := uint64(d) neg := d < 0 if neg { u = -u } if u < uint64(Second) { // Special case: if duration is smaller than a second, // use smaller units, like 1.2ms var prec int w-- buf[w] = 's' w-- switch { case u == 0: return "0s" case u < uint64(Microsecond): // print nanoseconds prec = 0 buf[w] = 'n' case u < uint64(Millisecond): // print microseconds prec = 3 // U+00B5 'µ' micro sign == 0xC2 0xB5 w-- // Need room for two bytes. copy(buf[w:], "µ") default: // print milliseconds prec = 6 buf[w] = 'm' } w, u = fmtFrac(buf[:w], u, prec) w = fmtInt(buf[:w], u) } else { w-- buf[w] = 's' w, u = fmtFrac(buf[:w], u, 9) // u is now integer seconds w = fmtInt(buf[:w], u%60) u /= 60 // u is now integer minutes if u > 0 { w-- buf[w] = 'm' w = fmtInt(buf[:w], u%60) u /= 60 // u is now integer hours // Stop at hours because days can be different lengths. if u > 0 { w-- buf[w] = 'h' w = fmtInt(buf[:w], u) } } } if neg { w-- buf[w] = '-' } return string(buf[w:]) } // fmtFrac formats the fraction of v/10**prec (e.g., ".12345") into the // tail of buf, omitting trailing zeros. It omits the decimal // point too when the fraction is 0. It returns the index where the // output bytes begin and the value v/10**prec. func fmtFrac(buf []byte, v uint64, prec int) (nw int, nv uint64) { // Omit trailing zeros up to and including decimal point. w := len(buf) print := false for i := 0; i < prec; i++ { digit := v % 10 print = print || digit != 0 if print { w-- buf[w] = byte(digit) + '0' } v /= 10 } if print { w-- buf[w] = '.' } return w, v } // fmtInt formats v into the tail of buf. // It returns the index where the output begins. func fmtInt(buf []byte, v uint64) int { w := len(buf) if v == 0 { w-- buf[w] = '0' } else { for v > 0 { w-- buf[w] = byte(v%10) + '0' v /= 10 } } return w } // Nanoseconds returns the duration as an integer nanosecond count. func (d Duration) Nanoseconds() int64 { return int64(d) } // These methods return float64 because the dominant // use case is for printing a floating point number like 1.5s, and // a truncation to integer would make them not useful in those cases. // Splitting the integer and fraction ourselves guarantees that // converting the returned float64 to an integer rounds the same // way that a pure integer conversion would have, even in cases // where, say, float64(d.Nanoseconds())/1e9 would have rounded // differently. // Seconds returns the duration as a floating point number of seconds. func (d Duration) Seconds() float64 { sec := d / Second nsec := d % Second return float64(sec) + float64(nsec)/1e9 } // Minutes returns the duration as a floating point number of minutes. func (d Duration) Minutes() float64 { min := d / Minute nsec := d % Minute return float64(min) + float64(nsec)/(60*1e9) } // Hours returns the duration as a floating point number of hours. func (d Duration) Hours() float64 { hour := d / Hour nsec := d % Hour return float64(hour) + float64(nsec)/(60*60*1e9) } // Truncate returns the result of rounding d toward zero to a multiple of m. // If m <= 0, Truncate returns d unchanged. func (d Duration) Truncate(m Duration) Duration { if m <= 0 { return d } return d - d%m } // lessThanHalf reports whether x+x < y but avoids overflow, // assuming x and y are both positive (Duration is signed). func lessThanHalf(x, y Duration) bool { return uint64(x)+uint64(x) < uint64(y) } // Round returns the result of rounding d to the nearest multiple of m. // The rounding behavior for halfway values is to round away from zero. // If the result exceeds the maximum (or minimum) // value that can be stored in a Duration, // Round returns the maximum (or minimum) duration. // If m <= 0, Round returns d unchanged. func (d Duration) Round(m Duration) Duration { if m <= 0 { return d } r := d % m if d < 0 { r = -r if lessThanHalf(r, m) { return d + r } if d1 := d - m + r; d1 < d { return d1 } return minDuration // overflow } if lessThanHalf(r, m) { return d - r } if d1 := d + m - r; d1 > d { return d1 } return maxDuration // overflow } // Add returns the time t+d. func (t Time) Add(d Duration) Time { dsec := int64(d / 1e9) nsec := t.nsec() + int32(d%1e9) if nsec >= 1e9 { dsec++ nsec -= 1e9 } else if nsec < 0 { dsec-- nsec += 1e9 } t.wall = t.wall&^nsecMask | uint64(nsec) // update nsec t.addSec(dsec) if t.wall&hasMonotonic != 0 { te := t.ext + int64(d) if d < 0 && te > t.ext || d > 0 && te < t.ext { // Monotonic clock reading now out of range; degrade to wall-only. t.stripMono() } else { t.ext = te } } return t } // Sub returns the duration t-u. If the result exceeds the maximum (or minimum) // value that can be stored in a Duration, the maximum (or minimum) duration // will be returned. // To compute t-d for a duration d, use t.Add(-d). func (t Time) Sub(u Time) Duration { if t.wall&u.wall&hasMonotonic != 0 { te := t.ext ue := u.ext d := Duration(te - ue) if d < 0 && te > ue { return maxDuration // t - u is positive out of range } if d > 0 && te < ue { return minDuration // t - u is negative out of range } return d } d := Duration(t.sec()-u.sec())*Second + Duration(t.nsec()-u.nsec()) // Check for overflow or underflow. switch { case u.Add(d).Equal(t): return d // d is correct case t.Before(u): return minDuration // t - u is negative out of range default: return maxDuration // t - u is positive out of range } } // Since returns the time elapsed since t. // It is shorthand for time.Now().Sub(t). func Since(t Time) Duration { return Now().Sub(t) } // Until returns the duration until t. // It is shorthand for t.Sub(time.Now()). func Until(t Time) Duration { return t.Sub(Now()) } // AddDate returns the time corresponding to adding the // given number of years, months, and days to t. // For example, AddDate(-1, 2, 3) applied to January 1, 2011 // returns March 4, 2010. // // AddDate normalizes its result in the same way that Date does, // so, for example, adding one month to October 31 yields // December 1, the normalized form for November 31. func (t Time) AddDate(years int, months int, days int) Time { year, month, day := t.Date() hour, min, sec := t.Clock() return Date(year+years, month+Month(months), day+days, hour, min, sec, int(t.nsec()), t.Location()) } const ( secondsPerMinute = 60 secondsPerHour = 60 * 60 secondsPerDay = 24 * secondsPerHour secondsPerWeek = 7 * secondsPerDay daysPer400Years = 365*400 + 97 daysPer100Years = 365*100 + 24 daysPer4Years = 365*4 + 1 ) // date computes the year, day of year, and when full=true, // the month and day in which t occurs. func (t Time) date(full bool) (year int, month Month, day int, yday int) { return absDate(t.abs(), full) } // absDate is like date but operates on an absolute time. func absDate(abs uint64, full bool) (year int, month Month, day int, yday int) { // Split into time and day. d := abs / secondsPerDay // Account for 400 year cycles. n := d / daysPer400Years y := 400 * n d -= daysPer400Years * n // Cut off 100-year cycles. // The last cycle has one extra leap year, so on the last day // of that year, day / daysPer100Years will be 4 instead of 3. // Cut it back down to 3 by subtracting n>>2. n = d / daysPer100Years n -= n >> 2 y += 100 * n d -= daysPer100Years * n // Cut off 4-year cycles. // The last cycle has a missing leap year, which does not // affect the computation. n = d / daysPer4Years y += 4 * n d -= daysPer4Years * n // Cut off years within a 4-year cycle. // The last year is a leap year, so on the last day of that year, // day / 365 will be 4 instead of 3. Cut it back down to 3 // by subtracting n>>2. n = d / 365 n -= n >> 2 y += n d -= 365 * n year = int(int64(y) + absoluteZeroYear) yday = int(d) if !full { return } day = yday if isLeap(year) { // Leap year switch { case day > 31+29-1: // After leap day; pretend it wasn't there. day-- case day == 31+29-1: // Leap day. month = February day = 29 return } } // Estimate month on assumption that every month has 31 days. // The estimate may be too low by at most one month, so adjust. month = Month(day / 31) end := int(daysBefore[month+1]) var begin int if day >= end { month++ begin = end } else { begin = int(daysBefore[month]) } month++ // because January is 1 day = day - begin + 1 return } // daysBefore[m] counts the number of days in a non-leap year // before month m begins. There is an entry for m=12, counting // the number of days before January of next year (365). var daysBefore = [...]int32{ 0, 31, 31 + 28, 31 + 28 + 31, 31 + 28 + 31 + 30, 31 + 28 + 31 + 30 + 31, 31 + 28 + 31 + 30 + 31 + 30, 31 + 28 + 31 + 30 + 31 + 30 + 31, 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31, 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30, 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31, 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30, 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31, } func daysIn(m Month, year int) int { if m == February && isLeap(year) { return 29 } return int(daysBefore[m] - daysBefore[m-1]) } // Provided by package runtime. func now() (sec int64, nsec int32, mono int64) // Now returns the current local time. func Now() Time { sec, nsec, mono := now() sec += unixToInternal - minWall if uint64(sec)>>33 != 0 { return Time{uint64(nsec), sec + minWall, Local} } return Time{hasMonotonic | uint64(sec)<<nsecShift | uint64(nsec), mono, Local} } func unixTime(sec int64, nsec int32) Time { return Time{uint64(nsec), sec + unixToInternal, Local} } // UTC returns t with the location set to UTC. func (t Time) UTC() Time { t.setLoc(&utcLoc) return t } // Local returns t with the location set to local time. func (t Time) Local() Time { t.setLoc(Local) return t } // In returns a copy of t representating the same time instant, but // with the copy's location information set to loc for display // purposes. // // In panics if loc is nil. func (t Time) In(loc *Location) Time { if loc == nil { panic("time: missing Location in call to Time.In") } t.setLoc(loc) return t } // Location returns the time zone information associated with t. func (t Time) Location() *Location { l := t.loc if l == nil { l = UTC } return l } // Zone computes the time zone in effect at time t, returning the abbreviated // name of the zone (such as "CET") and its offset in seconds east of UTC. func (t Time) Zone() (name string, offset int) { name, offset, _, _ = t.loc.lookup(t.unixSec()) return } // Unix returns t as a Unix time, the number of seconds elapsed // since January 1, 1970 UTC. The result does not depend on the // location associated with t. func (t Time) Unix() int64 { return t.unixSec() } // UnixNano returns t as a Unix time, the number of nanoseconds elapsed // since January 1, 1970 UTC. The result is undefined if the Unix time // in nanoseconds cannot be represented by an int64 (a date before the year // 1678 or after 2262). Note that this means the result of calling UnixNano // on the zero Time is undefined. The result does not depend on the // location associated with t. func (t Time) UnixNano() int64 { return (t.unixSec())*1e9 + int64(t.nsec()) } const timeBinaryVersion byte = 1 // MarshalBinary implements the encoding.BinaryMarshaler interface. func (t Time) MarshalBinary() ([]byte, error) { var offsetMin int16 // minutes east of UTC. -1 is UTC. if t.Location() == UTC { offsetMin = -1 } else { _, offset := t.Zone() if offset%60 != 0 { return nil, errors.New("Time.MarshalBinary: zone offset has fractional minute") } offset /= 60 if offset < -32768 || offset == -1 || offset > 32767 { return nil, errors.New("Time.MarshalBinary: unexpected zone offset") } offsetMin = int16(offset) } sec := t.sec() nsec := t.nsec() enc := []byte{ timeBinaryVersion, // byte 0 : version byte(sec >> 56), // bytes 1-8: seconds byte(sec >> 48), byte(sec >> 40), byte(sec >> 32), byte(sec >> 24), byte(sec >> 16), byte(sec >> 8), byte(sec), byte(nsec >> 24), // bytes 9-12: nanoseconds byte(nsec >> 16), byte(nsec >> 8), byte(nsec), byte(offsetMin >> 8), // bytes 13-14: zone offset in minutes byte(offsetMin), } return enc, nil } // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. func (t *Time) UnmarshalBinary(data []byte) error { buf := data if len(buf) == 0 { return errors.New("Time.UnmarshalBinary: no data") } if buf[0] != timeBinaryVersion { return errors.New("Time.UnmarshalBinary: unsupported version") } if len(buf) != /*version*/ 1+ /*sec*/ 8+ /*nsec*/ 4+ /*zone offset*/ 2 { return errors.New("Time.UnmarshalBinary: invalid length") } buf = buf[1:] sec := int64(buf[7]) | int64(buf[6])<<8 | int64(buf[5])<<16 | int64(buf[4])<<24 | int64(buf[3])<<32 | int64(buf[2])<<40 | int64(buf[1])<<48 | int64(buf[0])<<56 buf = buf[8:] nsec := int32(buf[3]) | int32(buf[2])<<8 | int32(buf[1])<<16 | int32(buf[0])<<24 buf = buf[4:] offset := int(int16(buf[1])|int16(buf[0])<<8) * 60 *t = Time{} t.wall = uint64(nsec) t.ext = sec if offset == -1*60 { t.setLoc(&utcLoc) } else if _, localoff, _, _ := Local.lookup(t.unixSec()); offset == localoff { t.setLoc(Local) } else { t.setLoc(FixedZone("", offset)) } return nil } // TODO(rsc): Remove GobEncoder, GobDecoder, MarshalJSON, UnmarshalJSON in Go 2. // The same semantics will be provided by the generic MarshalBinary, MarshalText, // UnmarshalBinary, UnmarshalText. // GobEncode implements the gob.GobEncoder interface. func (t Time) GobEncode() ([]byte, error) { return t.MarshalBinary() } // GobDecode implements the gob.GobDecoder interface. func (t *Time) GobDecode(data []byte) error { return t.UnmarshalBinary(data) } // MarshalJSON implements the json.Marshaler interface. // The time is a quoted string in RFC 3339 format, with sub-second precision added if present. func (t Time) MarshalJSON() ([]byte, error) { if y := t.Year(); y < 0 || y >= 10000 { // RFC 3339 is clear that years are 4 digits exactly. // See golang.org/issue/4556#c15 for more discussion. return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]") } b := make([]byte, 0, len(RFC3339Nano)+2) b = append(b, '"') b = t.AppendFormat(b, RFC3339Nano) b = append(b, '"') return b, nil } // UnmarshalJSON implements the json.Unmarshaler interface. // The time is expected to be a quoted string in RFC 3339 format. func (t *Time) UnmarshalJSON(data []byte) error { // Ignore null, like in the main JSON package. if string(data) == "null" { return nil } // Fractional seconds are handled implicitly by Parse. var err error *t, err = Parse(`"`+RFC3339+`"`, string(data)) return err } // MarshalText implements the encoding.TextMarshaler interface. // The time is formatted in RFC 3339 format, with sub-second precision added if present. func (t Time) MarshalText() ([]byte, error) { if y := t.Year(); y < 0 || y >= 10000 { return nil, errors.New("Time.MarshalText: year outside of range [0,9999]") } b := make([]byte, 0, len(RFC3339Nano)) return t.AppendFormat(b, RFC3339Nano), nil } // UnmarshalText implements the encoding.TextUnmarshaler interface. // The time is expected to be in RFC 3339 format. func (t *Time) UnmarshalText(data []byte) error { // Fractional seconds are handled implicitly by Parse. var err error *t, err = Parse(RFC3339, string(data)) return err } // Unix returns the local Time corresponding to the given Unix time, // sec seconds and nsec nanoseconds since January 1, 1970 UTC. // It is valid to pass nsec outside the range [0, 999999999]. // Not all sec values have a corresponding time value. One such // value is 1<<63-1 (the largest int64 value). func Unix(sec int64, nsec int64) Time { if nsec < 0 || nsec >= 1e9 { n := nsec / 1e9 sec += n nsec -= n * 1e9 if nsec < 0 { nsec += 1e9 sec-- } } return unixTime(sec, int32(nsec)) } func isLeap(year int) bool { return year%4 == 0 && (year%100 != 0 || year%400 == 0) } // norm returns nhi, nlo such that // hi * base + lo == nhi * base + nlo // 0 <= nlo < base func norm(hi, lo, base int) (nhi, nlo int) { if lo < 0 { n := (-lo-1)/base + 1 hi -= n lo += n * base } if lo >= base { n := lo / base hi += n lo -= n * base } return hi, lo } // Date returns the Time corresponding to // yyyy-mm-dd hh:mm:ss + nsec nanoseconds // in the appropriate zone for that time in the given location. // // The month, day, hour, min, sec, and nsec values may be outside // their usual ranges and will be normalized during the conversion. // For example, October 32 converts to November 1. // // A daylight savings time transition skips or repeats times. // For example, in the United States, March 13, 2011 2:15am never occurred, // while November 6, 2011 1:15am occurred twice. In such cases, the // choice of time zone, and therefore the time, is not well-defined. // Date returns a time that is correct in one of the two zones involved // in the transition, but it does not guarantee which. // // Date panics if loc is nil. func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) Time { if loc == nil { panic("time: missing Location in call to Date") } // Normalize month, overflowing into year. m := int(month) - 1 year, m = norm(year, m, 12) month = Month(m) + 1 // Normalize nsec, sec, min, hour, overflowing into day. sec, nsec = norm(sec, nsec, 1e9) min, sec = norm(min, sec, 60) hour, min = norm(hour, min, 60) day, hour = norm(day, hour, 24) y := uint64(int64(year) - absoluteZeroYear) // Compute days since the absolute epoch. // Add in days from 400-year cycles. n := y / 400 y -= 400 * n d := daysPer400Years * n // Add in 100-year cycles. n = y / 100 y -= 100 * n d += daysPer100Years * n // Add in 4-year cycles. n = y / 4 y -= 4 * n d += daysPer4Years * n // Add in non-leap years. n = y d += 365 * n // Add in days before this month. d += uint64(daysBefore[month-1]) if isLeap(year) && month >= March { d++ // February 29 } // Add in days before today. d += uint64(day - 1) // Add in time elapsed today. abs := d * secondsPerDay abs += uint64(hour*secondsPerHour + min*secondsPerMinute + sec) unix := int64(abs) + (absoluteToInternal + internalToUnix) // Look for zone offset for t, so we can adjust to UTC. // The lookup function expects UTC, so we pass t in the // hope that it will not be too close to a zone transition, // and then adjust if it is. _, offset, start, end := loc.lookup(unix) if offset != 0 { switch utc := unix - int64(offset); { case utc < start: _, offset, _, _ = loc.lookup(start - 1) case utc >= end: _, offset, _, _ = loc.lookup(end) } unix -= int64(offset) } t := unixTime(unix, int32(nsec)) t.setLoc(loc) return t } // Truncate returns the result of rounding t down to a multiple of d (since the zero time). // If d <= 0, Truncate returns t stripped of any monotonic clock reading but otherwise unchanged. // // Truncate operates on the time as an absolute duration since the // zero time; it does not operate on the presentation form of the // time. Thus, Truncate(Hour) may return a time with a non-zero // minute, depending on the time's Location. func (t Time) Truncate(d Duration) Time { t.stripMono() if d <= 0 { return t } _, r := div(t, d) return t.Add(-r) } // Round returns the result of rounding t to the nearest multiple of d (since the zero time). // The rounding behavior for halfway values is to round up. // If d <= 0, Round returns t stripped of any monotonic clock reading but otherwise unchanged. // // Round operates on the time as an absolute duration since the // zero time; it does not operate on the presentation form of the // time. Thus, Round(Hour) may return a time with a non-zero // minute, depending on the time's Location. func (t Time) Round(d Duration) Time { t.stripMono() if d <= 0 { return t } _, r := div(t, d) if lessThanHalf(r, d) { return t.Add(-r) } return t.Add(d - r) } // div divides t by d and returns the quotient parity and remainder. // We don't use the quotient parity anymore (round half up instead of round to even) // but it's still here in case we change our minds. func div(t Time, d Duration) (qmod2 int, r Duration) { neg := false nsec := t.nsec() sec := t.sec() if sec < 0 { // Operate on absolute value. neg = true sec = -sec nsec = -nsec if nsec < 0 { nsec += 1e9 sec-- // sec >= 1 before the -- so safe } } switch { // Special case: 2d divides 1 second. case d < Second && Second%(d+d) == 0: qmod2 = int(nsec/int32(d)) & 1 r = Duration(nsec % int32(d)) // Special case: d is a multiple of 1 second. case d%Second == 0: d1 := int64(d / Second) qmod2 = int(sec/d1) & 1 r = Duration(sec%d1)*Second + Duration(nsec) // General case. // This could be faster if more cleverness were applied, // but it's really only here to avoid special case restrictions in the API. // No one will care about these cases. default: // Compute nanoseconds as 128-bit number. sec := uint64(sec) tmp := (sec >> 32) * 1e9 u1 := tmp >> 32 u0 := tmp << 32 tmp = (sec & 0xFFFFFFFF) * 1e9 u0x, u0 := u0, u0+tmp if u0 < u0x { u1++ } u0x, u0 = u0, u0+uint64(nsec) if u0 < u0x { u1++ } // Compute remainder by subtracting r<<k for decreasing k. // Quotient parity is whether we subtract on last round. d1 := uint64(d) for d1>>63 != 1 { d1 <<= 1 } d0 := uint64(0) for { qmod2 = 0 if u1 > d1 || u1 == d1 && u0 >= d0 { // subtract qmod2 = 1 u0x, u0 = u0, u0-d0 if u0 > u0x { u1-- } u1 -= d1 } if d1 == 0 && d0 == uint64(d) { break } d0 >>= 1 d0 |= (d1 & 1) << 63 d1 >>= 1 } r = Duration(u0) } if neg && r != 0 { // If input was negative and not an exact multiple of d, we computed q, r such that // q*d + r = -t // But the right answers are given by -(q-1), d-r: // q*d + r = -t // -q*d - r = t // -(q-1)*d + (d - r) = t qmod2 ^= 1 r = d - r } return }