simhash算法c语言

以下是simhash算法的C语言实现代码：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define HASH_BITS 64
#define BLOCK_SIZE 4

typedef unsigned long long uint64_t;

typedef struct {
    uint64_t hash[HASH_BITS/BLOCK_SIZE];
} SimHash;

uint64_t murmur_hash(const char *data, uint64_t len, uint64_t seed) {
    const uint64_t m = 0xc6a4a7935bd1e995ull;
    const int r = 47;

    uint64_t h = seed ^ (len * m);

    const uint64_t *data64 = (const uint64_t*)data;
    const uint64_t *end64 = data64 + (len/8);

    while (data64 != end64) {
        uint64_t k = *data64++;

        k *= m;
        k ^= k >> r;
        k *= m;

        h ^= k;
        h *= m;
    }

    const unsigned char *data8 = (const unsigned char*)data64;

    switch (len & 7) {
        case 7: h ^= ((uint64_t)data8[6]) << 48;
        case 6: h ^= ((uint64_t)data8[5]) << 40;
        case 5: h ^= ((uint64_t)data8[4]) << 32;
        case 4: h ^= ((uint64_t)data8[3]) << 24;
        case 3: h ^= ((uint64_t)data8[2]) << 16;
        case 2: h ^= ((uint64_t)data8[1]) << 8;
        case 1: h ^= ((uint64_t)data8[0]);
                h *= m;
    }

    h ^= h >> r;
    h *= m;
    h ^= h >> r;

    return h;
}

void simhash(const char *data, uint64_t len, SimHash *hash) {
    memset(hash, 0, sizeof(SimHash));
    for (int i = 0; i < len; i++) {
        uint64_t h = murmur_hash(data + i, 1, i);
        for (int j = 0; j < HASH_BITS; j += BLOCK_SIZE) {
            uint64_t bit = (h >> j) & ((1ull << BLOCK_SIZE) - 1);
            hash->hash[j/BLOCK_SIZE] += bit;
        }
    }
    for (int i = 0; i < HASH_BITS; i += BLOCK_SIZE) {
        uint64_t bit = (hash->hash[i/BLOCK_SIZE] > (len/2)) ? 1 : 0;
        hash->hash[i/BLOCK_SIZE] = bit;
    }
}

int hamming_distance(SimHash *a, SimHash *b) {
    int distance = 0;
    for (int i = 0; i < HASH_BITS/BLOCK_SIZE; i++) {
        uint64_t diff = a->hash[i] ^ b->hash[i];
        while (diff) {
            distance++;
            diff &= diff - 1;
        }
    }
    return distance;
}

int main() {
    char *data1 = "This is a test sentence";
    char *data2 = "This is another test sentence";
    char *data3 = "This is a completely different sentence";

    SimHash hash1, hash2, hash3;

    simhash(data1, strlen(data1), &hash1);
    simhash(data2, strlen(data2), &hash2);
    simhash(data3, strlen(data3), &hash3);

    printf("Hamming distance between sentence 1 and 2 is %d\n", hamming_distance(&hash1, &hash2));
    printf("Hamming distance between sentence 1 and 3 is %d\n", hamming_distance(&hash1, &hash3));
    printf("Hamming distance between sentence 2 and 3 is %d\n", hamming_distance(&hash2, &hash3));

    return 0;
}

该代码实现了simhash算法的核心部分，包括murmur哈希函数、simhash函数和hamming_distance函数。其中，simhash函数计算给定字符串的hash值，hamming_distance函数计算两个hash值之间的汉明距离。可以通过调用simhash函数计算文本的hash值，并通过hamming_distance函数计算文本之间的相似度。