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109 lines
3.1 KiB
C#
109 lines
3.1 KiB
C#
#region ============== License
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/***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is HashTableHashing.MurmurHash2.
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*
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* The Initial Developer of the Original Code is
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* Davy Landman.
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* Portions created by the Initial Developer are Copyright (C) 2009
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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*
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#endregion
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using System;
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using System.Text;
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namespace CodeImp.DoomBuilder
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{
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internal static class MurmurHash2
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{
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private const UInt32 m = 0x5bd1e995;
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private const Int32 r = 24;
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public static UInt32 Hash(string data)
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{
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return Hash(Encoding.ASCII.GetBytes(data), 0xc58f1a7b);
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}
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private static unsafe UInt32 Hash(Byte[] data, UInt32 seed)
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{
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Int32 length = data.Length;
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if(length == 0) return 0;
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UInt32 h = seed ^ (UInt32)length;
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Int32 remainingBytes = length & 3; // mod 4
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Int32 numberOfLoops = length >> 2; // div 4
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fixed(byte* firstByte = &(data[0]))
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{
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UInt32* realData = (UInt32*)firstByte;
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while(numberOfLoops != 0)
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{
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UInt32 k = *realData;
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k *= m;
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k ^= k >> r;
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k *= m;
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h *= m;
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h ^= k;
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numberOfLoops--;
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realData++;
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}
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switch(remainingBytes)
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{
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case 3:
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h ^= (UInt16)(*realData);
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h ^= ((UInt32)(*(((Byte*)(realData)) + 2))) << 16;
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h *= m;
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break;
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case 2:
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h ^= (UInt16)(*realData);
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h *= m;
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break;
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case 1:
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h ^= *((Byte*)realData);
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h *= m;
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break;
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}
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}
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// Do a few final mixes of the hash to ensure the last few
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// bytes are well-incorporated.
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h ^= h >> 13;
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h *= m;
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h ^= h >> 15;
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return h;
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}
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}
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}
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