// 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 ( _ // for go:linkname ) // 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. // // Representations of a Time value saved by the GobEncode, MarshalBinary, // MarshalJSON, and MarshalText methods store the Time.Location's offset, but not // the location name. They therefore lose information about Daylight Saving Time. // // 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 ( *Time) () int32 { return int32(.wall & nsecMask) } // sec returns the time's seconds since Jan 1 year 1. func ( *Time) () int64 { if .wall&hasMonotonic != 0 { return wallToInternal + int64(.wall<<1>>(nsecShift+1)) } return .ext } // unixSec returns the time's seconds since Jan 1 1970 (Unix time). func ( *Time) () int64 { return .sec() + internalToUnix } // addSec adds d seconds to the time. func ( *Time) ( int64) { if .wall&hasMonotonic != 0 { := int64(.wall << 1 >> (nsecShift + 1)) := + if 0 <= && <= 1<<33-1 { .wall = .wall&nsecMask | uint64()<<nsecShift | hasMonotonic return } // Wall second now out of range for packed field. // Move to ext. .stripMono() } // TODO: Check for overflow. .ext += } // setLoc sets the location associated with the time. func ( *Time) ( *Location) { if == &utcLoc { = nil } .stripMono() .loc = } // stripMono strips the monotonic clock reading in t. func ( *Time) () { if .wall&hasMonotonic != 0 { .ext = .sec() .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 ( *Time) ( int64) { if .wall&hasMonotonic == 0 { := .ext if < minWall || maxWall < { return } .wall |= hasMonotonic | uint64(-minWall)<<nsecShift } .ext = } // 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 ( *Time) () int64 { if .wall&hasMonotonic == 0 { return 0 } return .ext } // After reports whether the time instant t is after u. func ( Time) ( Time) bool { if .wall&.wall&hasMonotonic != 0 { return .ext > .ext } := .sec() := .sec() return > || == && .nsec() > .nsec() } // Before reports whether the time instant t is before u. func ( Time) ( Time) bool { if .wall&.wall&hasMonotonic != 0 { return .ext < .ext } := .sec() := .sec() return < || == && .nsec() < .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 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 ( Time) ( Time) bool { if .wall&.wall&hasMonotonic != 0 { return .ext == .ext } return .sec() == .sec() && .nsec() == .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 ) // String returns the English name of the month ("January", "February", ...). func ( Month) () string { if January <= && <= December { return longMonthNames[-1] } := make([]byte, 20) := fmtInt(, uint64()) return "%!Month(" + string([:]) + ")" } // A Weekday specifies a day of the week (Sunday = 0, ...). type Weekday int const ( Sunday Weekday = iota Monday Tuesday Wednesday Thursday Friday Saturday ) // String returns the English name of the day ("Sunday", "Monday", ...). func ( Weekday) () string { if Sunday <= && <= Saturday { return longDayNames[] } := make([]byte, 20) := fmtInt(, uint64()) return "%!Weekday(" + string([:]) + ")" } // 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 ( Time) () bool { return .sec() == 0 && .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 ( Time) () uint64 { := .loc // Avoid function calls when possible. if == nil || == &localLoc { = .get() } := .unixSec() if != &utcLoc { if .cacheZone != nil && .cacheStart <= && < .cacheEnd { += int64(.cacheZone.offset) } else { , , , := .lookup() += int64() } } return uint64( + (unixToInternal + internalToAbsolute)) } // locabs is a combination of the Zone and abs methods, // extracting both return values from a single zone lookup. func ( Time) () ( string, int, uint64) { := .loc if == nil || == &localLoc { = .get() } // Avoid function call if we hit the local time cache. := .unixSec() if != &utcLoc { if .cacheZone != nil && .cacheStart <= && < .cacheEnd { = .cacheZone.name = .cacheZone.offset } else { , , _, _ = .lookup() } += int64() } else { = "UTC" } = uint64( + (unixToInternal + internalToAbsolute)) return } // Date returns the year, month, and day in which t occurs. func ( Time) () ( int, Month, int) { , , , _ = .date(true) return } // Year returns the year in which t occurs. func ( Time) () int { , , , := .date(false) return } // Month returns the month of the year specified by t. func ( Time) () Month { , , , := .date(true) return } // Day returns the day of the month specified by t. func ( Time) () int { , , , := .date(true) return } // Weekday returns the day of the week specified by t. func ( Time) () Weekday { return absWeekday(.abs()) } // absWeekday is like Weekday but operates on an absolute time. func absWeekday( uint64) Weekday { // January 1 of the absolute year, like January 1 of 2001, was a Monday. := ( + uint64(Monday)*secondsPerDay) % secondsPerWeek return Weekday(int() / 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 ( Time) () (, int) { // According to the rule that the first calendar week of a calendar year is // the week including the first Thursday of that year, and that the last one is // the week immediately preceding the first calendar week of the next calendar year. // See https://www.iso.org/obp/ui#iso:std:iso:8601:-1:ed-1:v1:en:term:3.1.1.23 for details. // weeks start with Monday // Monday Tuesday Wednesday Thursday Friday Saturday Sunday // 1 2 3 4 5 6 7 // +3 +2 +1 0 -1 -2 -3 // the offset to Thursday := .abs() := Thursday - absWeekday() // handle Sunday if == 4 { = -3 } // find the Thursday of the calendar week += uint64() * secondsPerDay , , , := absDate(, false) return , /7 + 1 } // Clock returns the hour, minute, and second within the day specified by t. func ( Time) () (, , int) { return absClock(.abs()) } // absClock is like clock but operates on an absolute time. func absClock( uint64) (, , int) { = int( % secondsPerDay) = / secondsPerHour -= * secondsPerHour = / secondsPerMinute -= * secondsPerMinute return } // Hour returns the hour within the day specified by t, in the range [0, 23]. func ( Time) () int { return int(.abs()%secondsPerDay) / secondsPerHour } // Minute returns the minute offset within the hour specified by t, in the range [0, 59]. func ( Time) () int { return int(.abs()%secondsPerHour) / secondsPerMinute } // Second returns the second offset within the minute specified by t, in the range [0, 59]. func ( Time) () int { return int(.abs() % secondsPerMinute) } // Nanosecond returns the nanosecond offset within the second specified by t, // in the range [0, 999999999]. func ( Time) () int { return int(.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 ( Time) () int { , , , := .date(false) return + 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 ( Duration) () string { // Largest time is 2540400h10m10.000000000s var [32]byte := len() := uint64() := < 0 if { = - } if < uint64(Second) { // Special case: if duration is smaller than a second, // use smaller units, like 1.2ms var int -- [] = 's' -- switch { case == 0: return "0s" case < uint64(Microsecond): // print nanoseconds = 0 [] = 'n' case < uint64(Millisecond): // print microseconds = 3 // U+00B5 'µ' micro sign == 0xC2 0xB5 -- // Need room for two bytes. copy([:], "µ") default: // print milliseconds = 6 [] = 'm' } , = fmtFrac([:], , ) = fmtInt([:], ) } else { -- [] = 's' , = fmtFrac([:], , 9) // u is now integer seconds = fmtInt([:], %60) /= 60 // u is now integer minutes if > 0 { -- [] = 'm' = fmtInt([:], %60) /= 60 // u is now integer hours // Stop at hours because days can be different lengths. if > 0 { -- [] = 'h' = fmtInt([:], ) } } } if { -- [] = '-' } return string([:]) } // 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( []byte, uint64, int) ( int, uint64) { // Omit trailing zeros up to and including decimal point. := len() := false for := 0; < ; ++ { := % 10 = || != 0 if { -- [] = byte() + '0' } /= 10 } if { -- [] = '.' } return , } // fmtInt formats v into the tail of buf. // It returns the index where the output begins. func fmtInt( []byte, uint64) int { := len() if == 0 { -- [] = '0' } else { for > 0 { -- [] = byte(%10) + '0' /= 10 } } return } // Nanoseconds returns the duration as an integer nanosecond count. func ( Duration) () int64 { return int64() } // Microseconds returns the duration as an integer microsecond count. func ( Duration) () int64 { return int64() / 1e3 } // Milliseconds returns the duration as an integer millisecond count. func ( Duration) () int64 { return int64() / 1e6 } // 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 ( Duration) () float64 { := / Second := % Second return float64() + float64()/1e9 } // Minutes returns the duration as a floating point number of minutes. func ( Duration) () float64 { := / Minute := % Minute return float64() + float64()/(60*1e9) } // Hours returns the duration as a floating point number of hours. func ( Duration) () float64 { := / Hour := % Hour return float64() + float64()/(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 ( Duration) ( Duration) Duration { if <= 0 { return } return - % } // lessThanHalf reports whether x+x < y but avoids overflow, // assuming x and y are both positive (Duration is signed). func lessThanHalf(, Duration) bool { return uint64()+uint64() < uint64() } // 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 ( Duration) ( Duration) Duration { if <= 0 { return } := % if < 0 { = - if lessThanHalf(, ) { return + } if := - + ; < { return } return minDuration // overflow } if lessThanHalf(, ) { return - } if := + - ; > { return } return maxDuration // overflow } // Add returns the time t+d. func ( Time) ( Duration) Time { := int64( / 1e9) := .nsec() + int32(%1e9) if >= 1e9 { ++ -= 1e9 } else if < 0 { -- += 1e9 } .wall = .wall&^nsecMask | uint64() // update nsec .addSec() if .wall&hasMonotonic != 0 { := .ext + int64() if < 0 && > .ext || > 0 && < .ext { // Monotonic clock reading now out of range; degrade to wall-only. .stripMono() } else { .ext = } } return } // 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 ( Time) ( Time) Duration { if .wall&.wall&hasMonotonic != 0 { := .ext := .ext := Duration( - ) if < 0 && > { return maxDuration // t - u is positive out of range } if > 0 && < { return minDuration // t - u is negative out of range } return } := Duration(.sec()-.sec())*Second + Duration(.nsec()-.nsec()) // Check for overflow or underflow. switch { case .Add().Equal(): return // d is correct case .Before(): 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 ( Time) Duration { var Time if .wall&hasMonotonic != 0 { // Common case optimization: if t has monotonic time, then Sub will use only it. = Time{hasMonotonic, runtimeNano() - startNano, nil} } else { = Now() } return .Sub() } // Until returns the duration until t. // It is shorthand for t.Sub(time.Now()). func ( Time) Duration { var Time if .wall&hasMonotonic != 0 { // Common case optimization: if t has monotonic time, then Sub will use only it. = Time{hasMonotonic, runtimeNano() - startNano, nil} } else { = Now() } return .Sub() } // 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 ( Time) ( int, int, int) Time { , , := .Date() , , := .Clock() return Date(+, +Month(), +, , , , int(.nsec()), .Location()) } const ( secondsPerMinute = 60 secondsPerHour = 60 * secondsPerMinute 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 ( Time) ( bool) ( int, Month, int, int) { return absDate(.abs(), ) } // absDate is like date but operates on an absolute time. func absDate( uint64, bool) ( int, Month, int, int) { // Split into time and day. := / secondsPerDay // Account for 400 year cycles. := / daysPer400Years := 400 * -= daysPer400Years * // 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. = / daysPer100Years -= >> 2 += 100 * -= daysPer100Years * // Cut off 4-year cycles. // The last cycle has a missing leap year, which does not // affect the computation. = / daysPer4Years += 4 * -= daysPer4Years * // 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. = / 365 -= >> 2 += -= 365 * = int(int64() + absoluteZeroYear) = int() if ! { return } = if isLeap() { // Leap year switch { case > 31+29-1: // After leap day; pretend it wasn't there. -- case == 31+29-1: // Leap day. = February = 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( / 31) := int(daysBefore[+1]) var int if >= { ++ = } else { = int(daysBefore[]) } ++ // because January is 1 = - + 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( Month, int) int { if == February && isLeap() { return 29 } return int(daysBefore[] - daysBefore[-1]) } // daysSinceEpoch takes a year and returns the number of days from // the absolute epoch to the start of that year. // This is basically (year - zeroYear) * 365, but accounting for leap days. func daysSinceEpoch( int) uint64 { := uint64(int64() - absoluteZeroYear) // Add in days from 400-year cycles. := / 400 -= 400 * := daysPer400Years * // Add in 100-year cycles. = / 100 -= 100 * += daysPer100Years * // Add in 4-year cycles. = / 4 -= 4 * += daysPer4Years * // Add in non-leap years. = += 365 * return } // Provided by package runtime. func now() ( int64, int32, int64) // runtimeNano returns the current value of the runtime clock in nanoseconds. //go:linkname runtimeNano runtime.nanotime func runtimeNano() int64 // Monotonic times are reported as offsets from startNano. // We initialize startNano to runtimeNano() - 1 so that on systems where // monotonic time resolution is fairly low (e.g. Windows 2008 // which appears to have a default resolution of 15ms), // we avoid ever reporting a monotonic time of 0. // (Callers may want to use 0 as "time not set".) var startNano int64 = runtimeNano() - 1 // Now returns the current local time. func () Time { , , := now() -= startNano += unixToInternal - minWall if uint64()>>33 != 0 { return Time{uint64(), + minWall, Local} } return Time{hasMonotonic | uint64()<<nsecShift | uint64(), , Local} } func unixTime( int64, int32) Time { return Time{uint64(), + unixToInternal, Local} } // UTC returns t with the location set to UTC. func ( Time) () Time { .setLoc(&utcLoc) return } // Local returns t with the location set to local time. func ( Time) () Time { .setLoc(Local) return } // In returns a copy of t representing the same time instant, but // with the copy's location information set to loc for display // purposes. // // In panics if loc is nil. func ( Time) ( *Location) Time { if == nil { panic("time: missing Location in call to Time.In") } .setLoc() return } // Location returns the time zone information associated with t. func ( Time) () *Location { := .loc if == nil { = UTC } return } // 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 ( Time) () ( string, int) { , , _, _ = .loc.lookup(.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. // Unix-like operating systems often record time as a 32-bit // count of seconds, but since the method here returns a 64-bit // value it is valid for billions of years into the past or future. func ( Time) () int64 { return .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 ( Time) () int64 { return (.unixSec())*1e9 + int64(.nsec()) } const timeBinaryVersion byte = 1 // MarshalBinary implements the encoding.BinaryMarshaler interface. func ( Time) () ([]byte, error) { var int16 // minutes east of UTC. -1 is UTC. if .Location() == UTC { = -1 } else { , := .Zone() if %60 != 0 { return nil, errors.New("Time.MarshalBinary: zone offset has fractional minute") } /= 60 if < -32768 || == -1 || > 32767 { return nil, errors.New("Time.MarshalBinary: unexpected zone offset") } = int16() } := .sec() := .nsec() := []byte{ timeBinaryVersion, // byte 0 : version byte( >> 56), // bytes 1-8: seconds byte( >> 48), byte( >> 40), byte( >> 32), byte( >> 24), byte( >> 16), byte( >> 8), byte(), byte( >> 24), // bytes 9-12: nanoseconds byte( >> 16), byte( >> 8), byte(), byte( >> 8), // bytes 13-14: zone offset in minutes byte(), } return , nil } // UnmarshalBinary implements the encoding.BinaryUnmarshaler interface. func ( *Time) ( []byte) error { := if len() == 0 { return errors.New("Time.UnmarshalBinary: no data") } if [0] != timeBinaryVersion { return errors.New("Time.UnmarshalBinary: unsupported version") } if len() != /*version*/ 1+ /*sec*/ 8+ /*nsec*/ 4+ /*zone offset*/ 2 { return errors.New("Time.UnmarshalBinary: invalid length") } = [1:] := int64([7]) | int64([6])<<8 | int64([5])<<16 | int64([4])<<24 | int64([3])<<32 | int64([2])<<40 | int64([1])<<48 | int64([0])<<56 = [8:] := int32([3]) | int32([2])<<8 | int32([1])<<16 | int32([0])<<24 = [4:] := int(int16([1])|int16([0])<<8) * 60 * = Time{} .wall = uint64() .ext = if == -1*60 { .setLoc(&utcLoc) } else if , , , := Local.lookup(.unixSec()); == { .setLoc(Local) } else { .setLoc(FixedZone("", )) } 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 ( Time) () ([]byte, error) { return .MarshalBinary() } // GobDecode implements the gob.GobDecoder interface. func ( *Time) ( []byte) error { return .UnmarshalBinary() } // MarshalJSON implements the json.Marshaler interface. // The time is a quoted string in RFC 3339 format, with sub-second precision added if present. func ( Time) () ([]byte, error) { if := .Year(); < 0 || >= 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]") } := make([]byte, 0, len(RFC3339Nano)+2) = append(, '"') = .AppendFormat(, RFC3339Nano) = append(, '"') return , nil } // UnmarshalJSON implements the json.Unmarshaler interface. // The time is expected to be a quoted string in RFC 3339 format. func ( *Time) ( []byte) error { // Ignore null, like in the main JSON package. if string() == "null" { return nil } // Fractional seconds are handled implicitly by Parse. var error *, = Parse(`"`+RFC3339+`"`, string()) return } // MarshalText implements the encoding.TextMarshaler interface. // The time is formatted in RFC 3339 format, with sub-second precision added if present. func ( Time) () ([]byte, error) { if := .Year(); < 0 || >= 10000 { return nil, errors.New("Time.MarshalText: year outside of range [0,9999]") } := make([]byte, 0, len(RFC3339Nano)) return .AppendFormat(, RFC3339Nano), nil } // UnmarshalText implements the encoding.TextUnmarshaler interface. // The time is expected to be in RFC 3339 format. func ( *Time) ( []byte) error { // Fractional seconds are handled implicitly by Parse. var error *, = Parse(RFC3339, string()) return } // 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 ( int64, int64) Time { if < 0 || >= 1e9 { := / 1e9 += -= * 1e9 if < 0 { += 1e9 -- } } return unixTime(, int32()) } func isLeap( int) bool { return %4 == 0 && (%100 != 0 || %400 == 0) } // norm returns nhi, nlo such that // hi * base + lo == nhi * base + nlo // 0 <= nlo < base func norm(, , int) (, int) { if < 0 { := (--1)/ + 1 -= += * } if >= { := / += -= * } return , } // 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 ( int, Month, , , , , int, *Location) Time { if == nil { panic("time: missing Location in call to Date") } // Normalize month, overflowing into year. := int() - 1 , = norm(, , 12) = Month() + 1 // Normalize nsec, sec, min, hour, overflowing into day. , = norm(, , 1e9) , = norm(, , 60) , = norm(, , 60) , = norm(, , 24) // Compute days since the absolute epoch. := daysSinceEpoch() // Add in days before this month. += uint64(daysBefore[-1]) if isLeap() && >= March { ++ // February 29 } // Add in days before today. += uint64( - 1) // Add in time elapsed today. := * secondsPerDay += uint64(*secondsPerHour + *secondsPerMinute + ) := int64() + (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. , , , := .lookup() if != 0 { switch := - int64(); { case < : _, , _, _ = .lookup( - 1) case >= : _, , _, _ = .lookup() } -= int64() } := unixTime(, int32()) .setLoc() return } // 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 ( Time) ( Duration) Time { .stripMono() if <= 0 { return } , := div(, ) return .Add(-) } // 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 ( Time) ( Duration) Time { .stripMono() if <= 0 { return } , := div(, ) if lessThanHalf(, ) { return .Add(-) } return .Add( - ) } // 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( Time, Duration) ( int, Duration) { := false := .nsec() := .sec() if < 0 { // Operate on absolute value. = true = - = - if < 0 { += 1e9 -- // sec >= 1 before the -- so safe } } switch { // Special case: 2d divides 1 second. case < Second && Second%(+) == 0: = int(/int32()) & 1 = Duration( % int32()) // Special case: d is a multiple of 1 second. case %Second == 0: := int64( / Second) = int(/) & 1 = Duration(%)*Second + Duration() // 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. := uint64() := ( >> 32) * 1e9 := >> 32 := << 32 = ( & 0xFFFFFFFF) * 1e9 , := , + if < { ++ } , = , +uint64() if < { ++ } // Compute remainder by subtracting r<<k for decreasing k. // Quotient parity is whether we subtract on last round. := uint64() for >>63 != 1 { <<= 1 } := uint64(0) for { = 0 if > || == && >= { // subtract = 1 , = , - if > { -- } -= } if == 0 && == uint64() { break } >>= 1 |= ( & 1) << 63 >>= 1 } = Duration() } if && != 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 ^= 1 = - } return }