vendor/github.com/google/uuid/version1.go

// 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"
)

// NewUUID returns a Version 1 UUID based on the current NodeID and clock
// sequence, and the current time.  If the NodeID has not been set by SetNodeID
// or SetNodeInterface then it will be set automatically.  If the NodeID cannot
// be set NewUUID returns nil.  If clock sequence has not been set by
// SetClockSequence then it will be set automatically.  If GetTime fails to
// return the current NewUUID returns nil and an error.
//
// In most cases, New should be used.
func NewUUID() (UUID, error) {
	nodeMu.Lock()
	if nodeID == zeroID {
		setNodeInterface("")
	}
	nodeMu.Unlock()

	var uuid UUID
	now, seq, err := GetTime()
	if err != nil {
		return uuid, err
	}

	timeLow := uint32(now & 0xffffffff)
	timeMid := uint16((now >> 32) & 0xffff)
	timeHi := uint16((now >> 48) & 0x0fff)
	timeHi |= 0x1000 // Version 1

	binary.BigEndian.PutUint32(uuid[0:], timeLow)
	binary.BigEndian.PutUint16(uuid[4:], timeMid)
	binary.BigEndian.PutUint16(uuid[6:], timeHi)
	binary.BigEndian.PutUint16(uuid[8:], seq)
	copy(uuid[10:], nodeID[:])

	return uuid, nil
}