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/*
"Murmur" hash provided by Austin, tanjent@gmail.com
http://murmurhash.googlepages.com/
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.
Updated to murmur2 hash - BP
*/
#include <libhashkit/common.h>
#ifdef HAVE_MURMUR_HASH
uint32_t hashkit_murmur(const char *key, size_t length, void *context)
{
/*
'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 uint32_t seed= (0xdeadbeef * (uint32_t)length);
const int r= 24;
// Initialize the hash to a 'random' value
uint32_t h= seed ^ (uint32_t)length;
// Mix 4 bytes at a time into the hash
const unsigned char * data= (const unsigned char *)key;
(void)context;
while(length >= 4)
{
unsigned int k = *(unsigned int *)data;
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
data += 4;
length -= 4;
}
// Handle the last few bytes of the input array
switch(length)
{
case 3: h ^= ((uint32_t)data[2]) << 16;
case 2: h ^= ((uint32_t)data[1]) << 8;
case 1: h ^= data[0];
h *= m;
default: break;
};
/*
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;
}
#else
uint32_t hashkit_murmur(const char *, size_t , void *)
{
return 0;
}
#endif
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