70 lines
1.5 KiB
C
70 lines
1.5 KiB
C
#ifndef __CXXMPH_MURMUR_HASH2__
|
|
#define __CXXMPH_MURMUR_HASH2__
|
|
|
|
//-----------------------------------------------------------------------------
|
|
// MurmurHash2, by Austin Appleby
|
|
|
|
// Note - This code makes a few assumptions about how your machine behaves -
|
|
|
|
// 1. We can read a 4-byte value from any address without crashing
|
|
// 2. sizeof(int) == 4
|
|
|
|
// And it has a few limitations -
|
|
|
|
// 1. It will not work incrementally.
|
|
// 2. It will not produce the same results on little-endian and big-endian
|
|
// machines.
|
|
|
|
unsigned int MurmurHash2 ( const void * key, int len, unsigned int seed )
|
|
{
|
|
// 'm' and 'r' are mixing constants generated offline.
|
|
// They're not really 'magic', they just happen to work well.
|
|
|
|
const unsigned int m = 0x5bd1e995;
|
|
const int r = 24;
|
|
|
|
// Initialize the hash to a 'random' value
|
|
|
|
unsigned int h = seed ^ len;
|
|
|
|
// Mix 4 bytes at a time into the hash
|
|
|
|
const unsigned char * data = (const unsigned char *)key;
|
|
|
|
while(len >= 4)
|
|
{
|
|
unsigned int k = *(unsigned int *)data;
|
|
|
|
k *= m;
|
|
k ^= k >> r;
|
|
k *= m;
|
|
|
|
h *= m;
|
|
h ^= k;
|
|
|
|
data += 4;
|
|
len -= 4;
|
|
}
|
|
|
|
// Handle the last few bytes of the input array
|
|
|
|
switch(len)
|
|
{
|
|
case 3: h ^= data[2] << 16;
|
|
case 2: h ^= data[1] << 8;
|
|
case 1: h ^= data[0];
|
|
h *= m;
|
|
};
|
|
|
|
// Do a few final mixes of the hash to ensure the last few
|
|
// bytes are well-incorporated.
|
|
|
|
h ^= h >> 13;
|
|
h *= m;
|
|
h ^= h >> 15;
|
|
|
|
return h;
|
|
}
|
|
|
|
#endif // __CXXMPH_MURMUR_HASH2__
|