Add MurmurHash3 implementation to hash.h/add hash.cpp.

1 files changed, 58 insertions, 0 deletions

diff --git a/src/hash.cpp b/src/hash.cpp
new file mode 100644
index 0000000000..bddd8abf38
--- /dev/null
+++ b/src/hash.cpp
@@ -0,0 +1,58 @@
+#include "hash.h"
+
+inline uint32_t ROTL32 ( uint32_t x, int8_t r )
+{
+    return (x << r) | (x >> (32 - r));
+}
+
+unsigned int MurmurHash3(unsigned int nHashSeed, const std::vector<unsigned char>& vDataToHash)
+{
+    // The following is MurmurHash3 (x86_32), see http://code.google.com/p/smhasher/source/browse/trunk/MurmurHash3.cpp
+    uint32_t h1 = nHashSeed;
+    const uint32_t c1 = 0xcc9e2d51;
+    const uint32_t c2 = 0x1b873593;
+
+    const int nblocks = vDataToHash.size() / 4;
+
+    //----------
+    // body
+    const uint32_t * blocks = (const uint32_t *)(&vDataToHash[0] + nblocks*4);
+
+    for(int i = -nblocks; i; i++)
+    {
+        uint32_t k1 = blocks[i];
+
+        k1 *= c1;
+        k1 = ROTL32(k1,15);
+        k1 *= c2;
+
+        h1 ^= k1;
+        h1 = ROTL32(h1,13); 
+        h1 = h1*5+0xe6546b64;
+    }
+
+    //----------
+    // tail
+    const uint8_t * tail = (const uint8_t*)(&vDataToHash[0] + nblocks*4);
+
+    uint32_t k1 = 0;
+
+    switch(vDataToHash.size() & 3)
+    {
+    case 3: k1 ^= tail[2] << 16;
+    case 2: k1 ^= tail[1] << 8;
+    case 1: k1 ^= tail[0];
+            k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
+    };
+
+    //----------
+    // finalization
+    h1 ^= vDataToHash.size();
+    h1 ^= h1 >> 16;
+    h1 *= 0x85ebca6b;
+    h1 ^= h1 >> 13;
+    h1 *= 0xc2b2ae35;
+    h1 ^= h1 >> 16;
+
+    return h1;
+}