/*]  Copyright (c) 2009-2010, Charles McGarvey  [**************************
**]  All rights reserved.
*
* vi:ts=4 sw=4 tw=75
*
* Distributable under the terms and conditions of the 2-clause BSD license;
* see the file COPYING for a complete text of the license.
*
**************************************************************************/

#include "hash.hh"


namespace moof {


// MurmurHash2, by Austin Appleby
// http://murmurhash.googlepages.com/

// This function is in the public domain.

// 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 hash_function::operator()(const void* key, int len,
								   unsigned int seed) const
{
	// '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;
} 


} // namespace moof