murmurhash3.c

/* This is MurmurHash3. The original C++ code was placed in the public domain
 * by its author, Austin Appleby.
 *
 * SPDX-License-Identifier: CC0-1.0
 * Source: https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp */

#include "murmurhash3.h"
#include "string.h"

static inline uint32_t fmix(uint32_t h)
{
    h ^= h >> 16;
    h *= 0x85ebca6b;
    h ^= h >> 13;
    h *= 0xc2b2ae35;
    h ^= h >> 16;

    return h;
}

static inline uint32_t rotl32(uint32_t x, int8_t r)
{
    return (x << r) | (x >> (32 - r));
}

uint32_t hash(const char* data, size_t len_)
{
    const int len = (int) len_;
    const int nblocks = len / 4;

    uint32_t h1 = 0xc062fb4a;

    uint32_t c1 = 0xcc9e2d51;
    uint32_t c2 = 0x1b873593;

    //----------
    // body

    for(int i = 0; i < nblocks; ++i)
    {
        uint32_t k1;
        memcpy(&k1, data + i * sizeof(k1), sizeof(k1));

        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*)(data + nblocks*4);

    uint32_t k1 = 0;

    switch(len & 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 ^= len;

    h1 = fmix(h1);

    return h1;
}