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khenaidoo59ce9dd2019-11-11 13:05:32 -05001// Copyright 2015 The etcd Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7// http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14
15package mvcc
16
17import "encoding/binary"
18
19// revBytesLen is the byte length of a normal revision.
20// First 8 bytes is the revision.main in big-endian format. The 9th byte
21// is a '_'. The last 8 bytes is the revision.sub in big-endian format.
22const revBytesLen = 8 + 1 + 8
23
24// A revision indicates modification of the key-value space.
25// The set of changes that share same main revision changes the key-value space atomically.
26type revision struct {
27 // main is the main revision of a set of changes that happen atomically.
28 main int64
29
30 // sub is the sub revision of a change in a set of changes that happen
31 // atomically. Each change has different increasing sub revision in that
32 // set.
33 sub int64
34}
35
36func (a revision) GreaterThan(b revision) bool {
37 if a.main > b.main {
38 return true
39 }
40 if a.main < b.main {
41 return false
42 }
43 return a.sub > b.sub
44}
45
46func newRevBytes() []byte {
47 return make([]byte, revBytesLen, markedRevBytesLen)
48}
49
50func revToBytes(rev revision, bytes []byte) {
51 binary.BigEndian.PutUint64(bytes, uint64(rev.main))
52 bytes[8] = '_'
53 binary.BigEndian.PutUint64(bytes[9:], uint64(rev.sub))
54}
55
56func bytesToRev(bytes []byte) revision {
57 return revision{
58 main: int64(binary.BigEndian.Uint64(bytes[0:8])),
59 sub: int64(binary.BigEndian.Uint64(bytes[9:])),
60 }
61}
62
63type revisions []revision
64
65func (a revisions) Len() int { return len(a) }
66func (a revisions) Less(i, j int) bool { return a[j].GreaterThan(a[i]) }
67func (a revisions) Swap(i, j int) { a[i], a[j] = a[j], a[i] }