murmurhash.c
No OneTemporary
Actions

Authored By

Unknown

Size

1 KB

Referenced Files

None

Subscribers

None

murmurhash.c
View Options

	//-----------------------------------------------------------------------------
	// 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
	// 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.

	unsigned int murmurhash2(const void * key, int len, const unsigned int 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;
	}