src/hash.cpp


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#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;
    if (vDataToHash.size() > 0)
    {
        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;
}