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scala/java/c++使用murmur3计算hash值保持跨语言之间一致

饶德元
2023-12-01

目标:在java/scala中对word计算出无符号数字(uint64)的hash值,与c++中计算的hash值一样

 

方案:

因为java没有uint64,而c++的murmur3是用的uint64,所以java这边直接asLong会出现负数,所以需要取原始二进制值,转换成guava提供的无符号long

scala端:

import com.google.common.hash.Hashing
import com.google.common.primitives.UnsignedLong
...
private def hash(word: String): String = {
      UnsignedLong.valueOf(Hashing.murmur3_128().hashString(word,StandardCharsets.UTF_8).asLong().toBinaryString,2).toString
}

c++端:

uint64_t hash(const std::string& word) {
    int str_len = word.length();
    const char* c_origin = word.c_str();
    uint64_t res[2];
    const uint32_t seed = 0;
    MurmurHash3_x64_128(c_origin, str_len, seed, res);
    return res[0];
}

...


void MurmurHash3_x64_128 ( const void * key, const int len,
                           const uint32_t seed, void * out )
{
    const uint8_t * data = (const uint8_t*)key;
    const int nblocks = len / 16;
    int i;

    uint64_t h1 = seed;
    uint64_t h2 = seed;

    uint64_t c1 = BIG_CONSTANT(0x87c37b91114253d5);
    uint64_t c2 = BIG_CONSTANT(0x4cf5ad432745937f);

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

    const uint64_t * blocks = (const uint64_t *)(data);

    for(i = 0; i < nblocks; i++)
    {
        uint64_t k1 = getblock(blocks,i*2+0);
        uint64_t k2 = getblock(blocks,i*2+1);

        k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;

        h1 = ROTL64(h1,27); h1 += h2; h1 = h1*5+0x52dce729;

        k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

        h2 = ROTL64(h2,31); h2 += h1; h2 = h2*5+0x38495ab5;
    }

    //----------
    // tail

    const uint8_t * tail = (const uint8_t*)(data + nblocks*16);

    uint64_t k1 = 0;
    uint64_t k2 = 0;

    switch(len & 15)
    {
        case 15: k2 ^= (uint64_t)(tail[14]) << 48;
        case 14: k2 ^= (uint64_t)(tail[13]) << 40;
        case 13: k2 ^= (uint64_t)(tail[12]) << 32;
        case 12: k2 ^= (uint64_t)(tail[11]) << 24;
        case 11: k2 ^= (uint64_t)(tail[10]) << 16;
        case 10: k2 ^= (uint64_t)(tail[ 9]) << 8;
        case  9: k2 ^= (uint64_t)(tail[ 8]) << 0;
            k2 *= c2; k2  = ROTL64(k2,33); k2 *= c1; h2 ^= k2;

        case  8: k1 ^= (uint64_t)(tail[ 7]) << 56;
        case  7: k1 ^= (uint64_t)(tail[ 6]) << 48;
        case  6: k1 ^= (uint64_t)(tail[ 5]) << 40;
        case  5: k1 ^= (uint64_t)(tail[ 4]) << 32;
        case  4: k1 ^= (uint64_t)(tail[ 3]) << 24;
        case  3: k1 ^= (uint64_t)(tail[ 2]) << 16;
        case  2: k1 ^= (uint64_t)(tail[ 1]) << 8;
        case  1: k1 ^= (uint64_t)(tail[ 0]) << 0;
            k1 *= c1; k1  = ROTL64(k1,31); k1 *= c2; h1 ^= k1;
    };

    //----------
    // finalization

    h1 ^= len; h2 ^= len;

    h1 += h2;
    h2 += h1;

    h1 = fmix64(h1);
    h2 = fmix64(h2);

    h1 += h2;
    h2 += h1;

    ((uint64_t*)out)[0] = h1;
    ((uint64_t*)out)[1] = h2;
}

 

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