#region ============== License

/***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is HashTableHashing.MurmurHash2.
 *
 * The Initial Developer of the Original Code is
 * Davy Landman.
 * Portions created by the Initial Developer are Copyright (C) 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
 * of those above. If you wish to allow use of your version of this file only
 * under the terms of either the GPL or the LGPL, and not to allow others to
 * use your version of this file under the terms of the MPL, indicate your
 * decision by deleting the provisions above and replace them with the notice
 * and other provisions required by the GPL or the LGPL. If you do not delete
 * the provisions above, a recipient may use your version of this file under
 * the terms of any one of the MPL, the GPL or the LGPL.
 *
 * ***** END LICENSE BLOCK ***** */

#endregion

using System;
using System.Text;

namespace CodeImp.DoomBuilder
{
	public static class MurmurHash2
	{
		private const UInt32 m = 0x5bd1e995;
		private const Int32 r = 24;

		public static UInt32 Hash(string data) 
		{
			return Hash(Encoding.ASCII.GetBytes(data), 0xc58f1a7b);
		}

		private static unsafe UInt32 Hash(Byte[] data, UInt32 seed) 
		{
			Int32 length = data.Length;
			if(length == 0) return 0;

			UInt32 h = seed ^ (UInt32)length;
			Int32 remainingBytes = length & 3; // mod 4
			Int32 numberOfLoops = length >> 2; // div 4
			
			fixed(byte* firstByte = &(data[0])) 
			{
				UInt32* realData = (UInt32*)firstByte;
				while(numberOfLoops != 0) 
				{
					UInt32 k = *realData;
					k *= m;
					k ^= k >> r;
					k *= m;

					h *= m;
					h ^= k;
					numberOfLoops--;
					realData++;
				}

				switch(remainingBytes) 
				{
					case 3:
						h ^= (UInt16)(*realData);
						h ^= ((UInt32)(*(((Byte*)(realData)) + 2))) << 16;
						h *= m;
						break;
					case 2:
						h ^= (UInt16)(*realData);
						h *= m;
						break;
					case 1:
						h ^= *((Byte*)realData);
						h *= m;
						break;
				}
			}

			// 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;
		}
	}
}
