Function MurmurHash3_x86_32

src/fl/stl/hash.h:22–76

----------------------------------------------------------------------------- MurmurHash3 x86 32-bit ----------------------------------------------------------------------------- Based on the public‐domain implementation by Austin Appleby: https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp

// Based on the public‐domain implementation by Austin Appleby:
// https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp
static inline u32 MurmurHash3_x86_32(const void *key, fl::size len,
                                          u32 seed = 0) {

    FL_DISABLE_WARNING_PUSH;
    FL_DISABLE_WARNING_IMPLICIT_FALLTHROUGH;

    const fl::u8 *data = static_cast<const fl::u8 *>(key);
    const int nblocks = int(len / 4);

    u32 h1 = seed;
    const u32 c1 = 0xcc9e2d51;
    const u32 c2 = 0x1b873593;

    // body
    const u32 *blocks = reinterpret_cast<const u32 *>(data); // ok reinterpret cast
    for (int i = 0; i < nblocks; ++i) {
        u32 k1 = blocks[i];
        k1 *= c1;
        k1 = (k1 << 15) | (k1 >> 17);
        k1 *= c2;

        h1 ^= k1;
        h1 = (h1 << 13) | (h1 >> 19);
        h1 = h1 * 5 + 0xe6546b64;
    }

    // tail
    const fl::u8 *tail = data + (nblocks * 4);
    u32 k1 = 0;
    switch (len & 3) {
    case 3:
        k1 ^= u32(tail[2]) << 16;
    case 2:
        k1 ^= u32(tail[1]) << 8;
    case 1:
        k1 ^= u32(tail[0]);
        k1 *= c1;
        k1 = (k1 << 15) | (k1 >> 17);
        k1 *= c2;
        h1 ^= k1;
    }

    // finalization
    h1 ^= u32(len);
    // fmix32
    h1 ^= h1 >> 16;
    h1 *= 0x85ebca6b;
    h1 ^= h1 >> 13;
    h1 *= 0xc2b2ae35;
    h1 ^= h1 >> 16;

    return h1;

    FL_DISABLE_WARNING_POP;
}

//-----------------------------------------------------------------------------
// Fast, cheap 32-bit integer hash (Thomas Wang)