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// Copyright 2023 Google Inc.  All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package uuid
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import "encoding/binary"
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// UUID version 6 is a field-compatible version of UUIDv1, reordered for improved DB locality.
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// It is expected that UUIDv6 will primarily be used in contexts where there are existing v1 UUIDs.
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// Systems that do not involve legacy UUIDv1 SHOULD consider using UUIDv7 instead.
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//
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// see https://datatracker.ietf.org/doc/html/draft-peabody-dispatch-new-uuid-format-03#uuidv6
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//
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// NewV6 returns a Version 6 UUID based on the current NodeID and clock
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// sequence, and the current time. If the NodeID has not been set by SetNodeID
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// or SetNodeInterface then it will be set automatically. If the NodeID cannot
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// be set NewV6 set NodeID is random bits automatically . If clock sequence has not been set by
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// SetClockSequence then it will be set automatically. If GetTime fails to
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// return the current NewV6 returns Nil and an error.
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func NewV6() (UUID, error) {
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	var uuid UUID
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	now, seq, err := GetTime()
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	if err != nil {
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		return uuid, err
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	}
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	/*
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	    0                   1                   2                   3
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	    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	   |                           time_high                           |
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	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	   |           time_mid            |      time_low_and_version     |
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	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	   |clk_seq_hi_res |  clk_seq_low  |         node (0-1)            |
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	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	   |                         node (2-5)                            |
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	   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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	*/
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	binary.BigEndian.PutUint64(uuid[0:], uint64(now))
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	binary.BigEndian.PutUint16(uuid[8:], seq)
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	uuid[6] = 0x60 | (uuid[6] & 0x0F)
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	uuid[8] = 0x80 | (uuid[8] & 0x3F)
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	nodeMu.Lock()
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	if nodeID == zeroID {
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		setNodeInterface("")
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	}
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	copy(uuid[10:], nodeID[:])
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	nodeMu.Unlock()
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	return uuid, nil
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}
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