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// Tweaked for VW and contributed by Ariel Faigon.
// Original at: http://murmurhash.googlepages.com/
//
// Based on 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
// (i.e non aligned access is supported) - this is not a problem
// on Intel/x86/AMD64 machines (including new Macs)
// 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.
//
#include <stdint.h> /* defines uint32_t etc */
#include <sys/types.h> /* defines size_t */
#define MIX(h,k,m) { k *= m; k ^= k >> r; k *= m; h *= m; h ^= k; }
uint32_t uniform_hash( const void *key, size_t len, uint32_t 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;
}
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