87 lines
1.9 KiB
C++
87 lines
1.9 KiB
C++
|
//-----------------------------------------------------------------------------
|
||
|
|
// MurmurHash2 was written by Austin Appleby, and is placed in the public
|
||
|
|
// domain. The author hereby disclaims copyright to this source code.
|
||
|
|
|
||
|
|
// 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.
|
||
|
|
|
||
|
|
#include "MurmurHash2.h"
|
||
|
|
|
||
|
|
//-----------------------------------------------------------------------------
|
||
|
|
// Platform-specific functions and macros
|
||
|
|
|
||
|
|
// Microsoft Visual Studio
|
||
|
|
|
||
|
|
#if defined(_MSC_VER)
|
||
|
|
|
||
|
|
#define BIG_CONSTANT(x) (x)
|
||
|
|
|
||
|
|
// Other compilers
|
||
|
|
|
||
|
|
#else // defined(_MSC_VER)
|
||
|
|
|
||
|
|
#define BIG_CONSTANT(x) (x##LLU)
|
||
|
|
|
||
|
|
#endif // !defined(_MSC_VER)
|
||
|
|
|
||
|
|
//-----------------------------------------------------------------------------
|
||
|
|
|
||
|
|
uint64_t MurmurHash2 ( const void* key, int len, uint32_t seed )
|
||
|
|
{
|
||
|
|
// 'm' and 'r' are mixing constants generated offline.
|
||
|
|
// They're not really 'magic', they just happen to work well.
|
||
|
|
|
||
|
|
const uint32_t m = 0x5bd1e995;
|
||
|
|
const int r = 24;
|
||
|
|
|
||
|
|
// Initialize the hash to a 'random' value
|
||
|
|
|
||
|
|
uint32_t h = seed ^ len;
|
||
|
|
|
||
|
|
// Mix 4 bytes at a time into the hash
|
||
|
|
const auto* data = (const unsigned char*) key;
|
||
|
|
while(len >= 4)
|
||
|
|
{
|
||
|
|
uint32_t k = *(uint32_t*)data;
|
||
|
|
|
||
|
|
k *= m;
|
||
|
|
k ^= k >> r;
|
||
|
|
k *= m;
|
||
|
|
|
||
|
|
h *= m;
|
||
|
|
h ^= k;
|
||
|
|
|
||
|
|
data += 4*sizeof(char);
|
||
|
|
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;
|
||
|
|
}
|
||
|
|
|
||
|
|
//-----------------------------------------------------------------------------
|