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[awesomized/libmemcached] / libhashkit / one_at_a_time.cc
1 /* vim:expandtab:shiftwidth=2:tabstop=2:smarttab:
2 *
3 * HashKit library
4 *
5 * Copyright (C) 2011-2012 Data Differential, http://datadifferential.com/
6 * Copyright (C) 2006-2009 Brian Aker All rights reserved.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions are
10 * met:
11 *
12 * * Redistributions of source code must retain the above copyright
13 * notice, this list of conditions and the following disclaimer.
14 *
15 * * Redistributions in binary form must reproduce the above
16 * copyright notice, this list of conditions and the following disclaimer
17 * in the documentation and/or other materials provided with the
18 * distribution.
19 *
20 * * The names of its contributors may not be used to endorse or
21 * promote products derived from this software without specific prior
22 * written permission.
23 *
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
25 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
26 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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36 */
37
38
39 /*
40 This has is Jenkin's "One at A time Hash".
41 http://en.wikipedia.org/wiki/Jenkins_hash_function
42 */
43
44 #include <libhashkit/common.h>
45
46 uint32_t hashkit_one_at_a_time(const char *key, size_t key_length, void *context)
47 {
48 const char *ptr= key;
49 uint32_t value= 0;
50 (void)context;
51
52 while (key_length--)
53 {
54 uint32_t val= (uint32_t) *ptr++;
55 value += val;
56 value += (value << 10);
57 value ^= (value >> 6);
58 }
59 value += (value << 3);
60 value ^= (value >> 11);
61 value += (value << 15);
62
63 return value;
64 }