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gcsdk/steamextra/tier1/murmurhash3.cpp

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+//======= Copyright <20> Valve Corporation, All rights reserved. =================
+//
+// Public domain MurmurHash3 by Austin Appleby is a very solid general-purpose
+// hash with a 32-bit output. References:
+// http://code.google.com/p/smhasher/ (home of MurmurHash3)
+// https://sites.google.com/site/murmurhash/avalanche
+// http://www.strchr.com/hash_functions 
+//
+//=============================================================================
+
+#include <stdafx.h>
+#include "murmurhash3.h"
+
+//-----------------------------------------------------------------------------
+
+uint32 MurmurHash3_32( const void * key, size_t len, uint32 seed, bool bCaselessStringVariant )
+{
+	const uint8 * data = (const uint8*)key;
+	const ptrdiff_t nblocks = len / 4;
+	uint32 uSourceBitwiseAndMask = 0xDFDFDFDF | ((uint32)bCaselessStringVariant - 1);
+
+	uint32 h1 = seed;
+
+	//----------
+	// body
+
+	const uint32 * blocks = (const uint32 *)(data + nblocks*4);
+
+	for(ptrdiff_t i = -nblocks; i; i++)
+	{
+		uint32 k1 = LittleDWord(blocks[i]);
+		k1 &= uSourceBitwiseAndMask;
+
+		k1 *= 0xcc9e2d51;
+		k1 = (k1 << 15) | (k1 >> 17);
+		k1 *= 0x1b873593;
+
+		h1 ^= k1;
+		h1 = (h1 << 13) | (h1 >> 19);
+		h1 = h1*5+0xe6546b64;
+	}
+
+	//----------
+	// tail
+
+	const uint8 * tail = (const uint8*)(data + nblocks*4);
+
+	uint32 k1 = 0;
+
+	switch(len & 3)
+	{
+	case 3: k1 ^= tail[2] << 16;
+	case 2: k1 ^= tail[1] << 8;
+	case 1: k1 ^= tail[0];
+		k1 &= uSourceBitwiseAndMask;
+		k1 *= 0xcc9e2d51;
+		k1 = (k1 << 15) | (k1 >> 17);
+		k1 *= 0x1b873593;
+		h1 ^= k1;
+	};
+
+	//----------
+	// finalization
+
+	h1 ^= len;
+
+	h1 ^= h1 >> 16;
+	h1 *= 0x85ebca6b;
+	h1 ^= h1 >> 13;
+	h1 *= 0xc2b2ae35;
+	h1 ^= h1 >> 16;
+
+	return h1;
+}