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//
// MurmurHash3, by Austin Appleby
//
// Originals at:
// http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
// http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.h
//
// Notes:
// 1) this code assumes 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) It produces different results on little-endian and big-endian machines.
//
// Adopted for VW and contributed by Ariel Faigon.
//
//-----------------------------------------------------------------------------
// MurmurHash3 was written by Austin Appleby, and is placed in the public
// domain. The author hereby disclaims copyright to this source code.
// Note - The x86 and x64 versions do _not_ produce the same results, as the
// algorithms are optimized for their respective platforms. You can still
// compile and run any of them on any platform, but your performance with the
// non-native version will be less than optimal.
//-----------------------------------------------------------------------------
#include <sys/types.h> /* defines size_t */
// Platform-specific functions and macros
#if defined(_MSC_VER) // Microsoft Visual Studio
# include <stdint.h>
# include <stdlib.h>
# define ROTL32(x,y) _rotl(x,y)
# define BIG_CONSTANT(x) (x)
#else // Other compilers
# include <stdint.h> /* defines uint32_t etc */
inline uint32_t rotl32(uint32_t x, int8_t r)
{
return (x << r) | (x >> (32 - r));
}
# define ROTL32(x,y) rotl32(x,y)
# define BIG_CONSTANT(x) (x##LLU)
#endif // !defined(_MSC_VER)
namespace MURMUR_HASH_3 {
//-----------------------------------------------------------------------------
// Block read - if your platform needs to do endian-swapping or can only
// handle aligned reads, do the conversion here
static inline uint32_t getblock(const uint32_t * p, int i)
{
return p[i];
}
//-----------------------------------------------------------------------------
// Finalization mix - force all bits of a hash block to avalanche
static inline uint32_t fmix(uint32_t h)
{
h ^= h >> 16;
h *= 0x85ebca6b;
h ^= h >> 13;
h *= 0xc2b2ae35;
h ^= h >> 16;
return h;
}
}
//-----------------------------------------------------------------------------
uint32_t uniform_hash(const void * key, size_t len, uint32_t seed)
{
const uint8_t * data = (const uint8_t*)key;
const int nblocks = (int)len / 4;
uint32_t h1 = seed;
const uint32_t c1 = 0xcc9e2d51;
const uint32_t c2 = 0x1b873593;
// --- body
const uint32_t * blocks = (const uint32_t *)(data + nblocks * 4);
for (int i = -nblocks; i; i++) {
uint32_t k1 = MURMUR_HASH_3::getblock(blocks, i);
k1 *= c1;
k1 = ROTL32(k1, 15);
k1 *= c2;
h1 ^= k1;
h1 = ROTL32(h1, 13);
h1 = h1 * 5 + 0xe6546b64;
}
// --- tail
const uint8_t * tail = (const uint8_t*)(data + nblocks * 4);
uint32_t k1 = 0;
switch (len & 3) {
case 3: k1 ^= tail[2] << 16;
case 2: k1 ^= tail[1] << 8;
case 1: k1 ^= tail[0];
k1 *= c1; k1 = ROTL32(k1, 15); k1 *= c2; h1 ^= k1;
}
// --- finalization
h1 ^= len;
return MURMUR_HASH_3::fmix(h1);
}
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