X-Git-Url: https://git.dogcows.com/gitweb?p=chaz%2Fyoink;a=blobdiff_plain;f=src%2Fmoof%2Fhash.cc;fp=src%2Fmoof%2Fhash.cc;h=dbbc9befae9b337a352ab65591b84bd81ba69d13;hp=0000000000000000000000000000000000000000;hb=831f04d4bc19a390415ac0bbac4331c7a65509bc;hpb=299af4f2047e767e5d79501c26444473bda64c64

diff --git a/src/moof/hash.cc b/src/moof/hash.cc
new file mode 100644
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--- /dev/null
+++ b/src/moof/hash.cc
@@ -0,0 +1,88 @@
+
+/*]  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
+