source: code/trunk/vendor/github.com/google/uuid/time.go@ 822

// Copyright 2016 Google Inc.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package uuid

import (
        "encoding/binary"
        "sync"
        "time"
)

// A Time represents a time as the number of 100's of nanoseconds since 15 Oct
// 1582.
type Time int64

const (
        lillian    = 2299160          // Julian day of 15 Oct 1582
        unix       = 2440587          // Julian day of 1 Jan 1970
        epoch      = unix - lillian   // Days between epochs
        g1582      = epoch * 86400    // seconds between epochs
        g1582ns100 = g1582 * 10000000 // 100s of a nanoseconds between epochs
)

var (
        timeMu   sync.Mutex
        lasttime uint64 // last time we returned
        clockSeq uint16 // clock sequence for this run

        timeNow = time.Now // for testing
)

// UnixTime converts t the number of seconds and nanoseconds using the Unix
// epoch of 1 Jan 1970.
func (t Time) UnixTime() (sec, nsec int64) {
        sec = int64(t - g1582ns100)
        nsec = (sec % 10000000) * 100
        sec /= 10000000
        return sec, nsec
}

// GetTime returns the current Time (100s of nanoseconds since 15 Oct 1582) and
// clock sequence as well as adjusting the clock sequence as needed.  An error
// is returned if the current time cannot be determined.
func GetTime() (Time, uint16, error) {
        defer timeMu.Unlock()
        timeMu.Lock()
        return getTime()
}

func getTime() (Time, uint16, error) {
        t := timeNow()

        // If we don't have a clock sequence already, set one.
        if clockSeq == 0 {
                setClockSequence(-1)
        }
        now := uint64(t.UnixNano()/100) + g1582ns100

        // If time has gone backwards with this clock sequence then we
        // increment the clock sequence
        if now <= lasttime {
                clockSeq = ((clockSeq + 1) & 0x3fff) | 0x8000
        }
        lasttime = now
        return Time(now), clockSeq, nil
}

// ClockSequence returns the current clock sequence, generating one if not
// already set.  The clock sequence is only used for Version 1 UUIDs.
//
// The uuid package does not use global static storage for the clock sequence or
// the last time a UUID was generated.  Unless SetClockSequence is used, a new
// random clock sequence is generated the first time a clock sequence is
// requested by ClockSequence, GetTime, or NewUUID.  (section 4.2.1.1)
func ClockSequence() int {
        defer timeMu.Unlock()
        timeMu.Lock()
        return clockSequence()
}

func clockSequence() int {
        if clockSeq == 0 {
                setClockSequence(-1)
        }
        return int(clockSeq & 0x3fff)
}

// SetClockSequence sets the clock sequence to the lower 14 bits of seq.  Setting to
// -1 causes a new sequence to be generated.
func SetClockSequence(seq int) {
        defer timeMu.Unlock()
        timeMu.Lock()
        setClockSequence(seq)
}

func setClockSequence(seq int) {
        if seq == -1 {
                var b [2]byte
                randomBits(b[:]) // clock sequence
                seq = int(b[0])<<8 | int(b[1])
        }
        oldSeq := clockSeq
        clockSeq = uint16(seq&0x3fff) | 0x8000 // Set our variant
        if oldSeq != clockSeq {
                lasttime = 0
        }
}

// Time returns the time in 100s of nanoseconds since 15 Oct 1582 encoded in
// uuid.  The time is only defined for version 1 and 2 UUIDs.
func (uuid UUID) Time() Time {
        time := int64(binary.BigEndian.Uint32(uuid[0:4]))
        time |= int64(binary.BigEndian.Uint16(uuid[4:6])) << 32
        time |= int64(binary.BigEndian.Uint16(uuid[6:8])&0xfff) << 48
        return Time(time)
}

// ClockSequence returns the clock sequence encoded in uuid.
// The clock sequence is only well defined for version 1 and 2 UUIDs.
func (uuid UUID) ClockSequence() int {
        return int(binary.BigEndian.Uint16(uuid[8:10])) & 0x3fff
}