1 // Copyright 2018 The gVisor 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 15 // Package jenkins implements Jenkins's one_at_a_time, non-cryptographic hash
16 // functions created by by Bob Jenkins.
17 //
18 // See https://en.wikipedia.org/wiki/Jenkins_hash_function#cite_note-dobbsx-1
19 package jenkins
20 21 import (
22 "hash"
23 )
24 25 // Sum32 represents Jenkins's one_at_a_time hash.
26 //
27 // Use the Sum32 type directly (as opposed to New32 below)
28 // to avoid allocations.
29 type Sum32 uint32
30 31 // New32 returns a new 32-bit Jenkins's one_at_a_time hash.Hash.
32 //
33 // Its Sum method will lay the value out in big-endian byte order.
34 func New32() hash.Hash32 {
35 var s Sum32
36 return &s
37 }
38 39 // Reset resets the hash to its initial state.
40 func (s *Sum32) Reset() { *s = 0 }
41 42 // Sum32 returns the hash value
43 func (s *Sum32) Sum32() uint32 {
44 sCopy := *s
45 46 sCopy += sCopy << 3
47 sCopy ^= sCopy >> 11
48 sCopy += sCopy << 15
49 50 return uint32(sCopy)
51 }
52 53 // Write adds more data to the running hash.
54 //
55 // It never returns an error.
56 func (s *Sum32) Write(data []byte) (int, error) {
57 sCopy := *s
58 for _, b := range data {
59 sCopy += Sum32(b)
60 sCopy += sCopy << 10
61 sCopy ^= sCopy >> 6
62 }
63 *s = sCopy
64 return len(data), nil
65 }
66 67 // Size returns the number of bytes Sum will return.
68 func (s *Sum32) Size() int { return 4 }
69 70 // BlockSize returns the hash's underlying block size.
71 func (s *Sum32) BlockSize() int { return 1 }
72 73 // Sum appends the current hash to in and returns the resulting slice.
74 //
75 // It does not change the underlying hash state.
76 func (s *Sum32) Sum(in []byte) []byte {
77 v := s.Sum32()
78 return append(in, byte(v>>24), byte(v>>16), byte(v>>8), byte(v))
79 }
80