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Dogcows Code - chaz/yoink/blob - src/Moof/Hash.cc
2 /*******************************************************************************
4 Copyright (c) 2009, Charles McGarvey
7 Redistribution and use in source and binary forms, with or without
8 modification, are permitted provided that the following conditions are met:
10 * Redistributions of source code must retain the above copyright notice,
11 this list of conditions and the following disclaimer.
12 * Redistributions in binary form must reproduce the above copyright notice,
13 this list of conditions and the following disclaimer in the documentation
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35 // MurmurHash2, by Austin Appleby
36 // http://murmurhash.googlepages.com/
38 // This function is in the public domain.
40 // Note - This code makes a few assumptions about how your machine behaves -
42 // 1. We can read a 4-byte value from any address without crashing
43 // 2. sizeof(int) == 4
45 // And it has a few limitations -
47 // 1. It will not work incrementally.
48 // 2. It will not produce the same results on little-endian and big-endian
51 unsigned getHash::operator()(const void* key
, int len
, unsigned int seed
) const
53 // 'm' and 'r' are mixing constants generated offline.
54 // They're not really 'magic', they just happen to work well.
56 const unsigned int m
= 0x5bd1e995;
59 // Initialize the hash to a 'random' value
61 unsigned int h
= seed
^ len
;
63 // Mix 4 bytes at a time into the hash
65 const unsigned char* data
= (const unsigned char*)key
;
69 unsigned int k
= *(unsigned int*)data
;
82 // Handle the last few bytes of the input array
86 case 3: h
^= data
[2] << 16;
87 case 2: h
^= data
[1] << 8;
92 // Do a few final mixes of the hash to ensure the last few
93 // bytes are well-incorporated.
105 /** vim: set ts=4 sw=4 tw=80: *************************************************/
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