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1 // Copyright (c) 2013, the Dart project authors. Please see the AUTHORS file | |
2 // for details. All rights reserved. Use of this source code is governed by a | |
3 // BSD-style license that can be found in the LICENSE file. | |
4 | |
5 part of html_common; | |
6 | |
7 /** | |
8 * This is the [Jenkins hash function][1] but using masking to keep | |
9 * values in SMI range. | |
10 * | |
11 * [1]: http://en.wikipedia.org/wiki/Jenkins_hash_function | |
12 * | |
13 * Use: | |
14 * Hash each value with the hash of the previous value, then get the final | |
15 * hash by calling finish. | |
16 * | |
17 * var hash = 0; | |
18 * for (var value in values) { | |
19 * hash = JenkinsSmiHash.combine(hash, value.hashCode); | |
20 * } | |
21 * hash = JenkinsSmiHash.finish(hash); | |
22 */ | |
23 class JenkinsSmiHash { | |
24 // TODO: Bug 11617- This class should be optimized and standardized elsewhere. | |
25 | |
26 static int combine(int hash, int value) { | |
27 hash = 0x1fffffff & (hash + value); | |
28 hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10)); | |
29 return hash ^ (hash >> 6); | |
30 } | |
31 | |
32 static int finish(int hash) { | |
33 hash = 0x1fffffff & (hash + ((0x03ffffff & hash) << 3)); | |
34 hash = hash ^ (hash >> 11); | |
35 return 0x1fffffff & (hash + ((0x00003fff & hash) << 15)); | |
36 } | |
37 | |
38 static int hash2(a, b) => finish(combine(combine(0, a), b)); | |
39 | |
40 static int hash4(a, b, c, d) => | |
41 finish(combine(combine(combine(combine(0, a), b), c), d)); | |
42 } | |
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