bx/include/bx/hash.h

/*
 * Copyright 2010-2011 Branimir Karadzic. All rights reserved.
 * License: http://www.opensource.org/licenses/BSD-2-Clause
 */

#ifndef __BX_HASH_H__
#define __BX_HASH_H__

#include "bx.h"

namespace bx
{
	// MurmurHash2 was written by Austin Appleby, and is placed in the public
	// domain. The author hereby disclaims copyright to this source code.
	#define MURMUR_M 0x5bd1e995
	#define MURMUR_R 24

	#define mmix(_h, _k) { _k *= MURMUR_M; _k ^= _k >> MURMUR_R; _k *= MURMUR_M; _h *= MURMUR_M; _h ^= _k; }

	class HashMurmur2A
	{
	public:
		void begin(uint32_t _seed = 0)
		{
			m_hash = _seed;
			m_tail = 0;
			m_count = 0;
			m_size = 0;
		}

		void add(const void* _data, int _len)
		{
			const uint8_t* data = (uint8_t*)_data;
			m_size += _len;

			mixTail(data, _len);

			while(_len >= 4)
			{
				uint32_t kk = *(uint32_t*)data;

				mmix(m_hash, kk);

				data += 4;
				_len -= 4;
			}

			mixTail(data, _len);
		}

		uint32_t end()
		{
			mmix(m_hash, m_tail);
			mmix(m_hash, m_size);

			m_hash ^= m_hash >> 13;
			m_hash *= MURMUR_M;
			m_hash ^= m_hash >> 15;

			return m_hash;
		}

	private:
		void mixTail(const uint8_t*& _data, int& _len)
		{
			while( _len && ((_len<4) || m_count) )
			{
				m_tail |= (*_data++) << (m_count * 8);

				m_count++;
				_len--;

				if(m_count == 4)
				{
					mmix(m_hash, m_tail);
					m_tail = 0;
					m_count = 0;
				}
			}
		}

		uint32_t m_hash;
		uint32_t m_tail;
		uint32_t m_count;
		uint32_t m_size;
	};

} // namespace bx

#endif // __BX_HASH_H__