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Diffstat (limited to 'src/libbasic/src/MurmurHash2.c')
-rw-r--r-- | src/libbasic/src/MurmurHash2.c | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/src/libbasic/src/MurmurHash2.c b/src/libbasic/src/MurmurHash2.c new file mode 100644 index 0000000000..9020793930 --- /dev/null +++ b/src/libbasic/src/MurmurHash2.c @@ -0,0 +1,86 @@ +//----------------------------------------------------------------------------- +// 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) + +//----------------------------------------------------------------------------- + +uint32_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 unsigned char * 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; + 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; +} |