c语言实现simhash

Simhash是一种文本相似度计算算法，可以用于文本去重、聚类等应用。下面是C语言实现Simhash的一种方式：

1. 首先需要对文本进行分词，可以使用分词库或自己实现。

2. 对每个词进行哈希，得到一个64位的哈希值。

3. 统计每个词的出现次数，并计算每个词的权重。

4. 对所有的哈希值进行加权求和，得到一个64位的Simhash值。

5. 对Simhash值进行降维，将64位的值降到32位或16位。

以下是一个简单的C语言实现示例：

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

#define HASH_BITS 64
#define SIMHASH_BITS 32

typedef unsigned long long uint64_t;

typedef struct {
    char *word;     // 词
    uint64_t hash;  // 哈希值
    int weight;     // 权重
} Word;

Word *split_words(char *text, int *n) {
    // TODO: 实现分词
}

uint64_t hash_word(char *word) {
    // TODO: 实现哈希算法
}

uint64_t simhash(Word *words, int n) {
    int i, j;
    uint64_t hash, simhash = 0;
    int bit_count[HASH_BITS] = {0};
    for (i = 0; i < n; i++) {
        hash = words[i].hash;
        for (j = 0; j < HASH_BITS; j++) {
            if (hash & (1ULL << j)) {
                bit_count[j] += words[i].weight;
            } else {
                bit_count[j] -= words[i].weight;
            }
        }
    }
    for (i = 0; i < SIMHASH_BITS; i++) {
        if (bit_count[i] > 0) {
            simhash |= (1ULL << i);
        }
    }
    return simhash;
}

uint64_t simhash32(uint64_t simhash) {
    // 将64位的Simhash值降到32位
    uint64_t mask = (1ULL << SIMHASH_BITS) - 1;
    uint64_t simhash32 = 0;
    int i;
    for (i = 0; i < HASH_BITS; i += 2) {
        simhash32 |= (((simhash >> i) & 3) * (i + 1));
    }
    simhash32 &= mask;
    return simhash32;
}

int main() {
    char *text1 = "This is a test.";
    char *text2 = "This is another test.";
    Word *words1, *words2;
    int n1, n2, i;
    uint64_t hash1, hash2, simhash1, simhash2, simhash32_1, simhash32_2;
    words1 = split_words(text1, &n1);
    words2 = split_words(text2, &n2);
    for (i = 0; i < n1; i++) {
        words1[i].hash = hash_word(words1[i].word);
        words1[i].weight = 1;
    }
    for (i = 0; i < n2; i++) {
        words2[i].hash = hash_word(words2[i].word);
        words2[i].weight = 1;
    }
    simhash1 = simhash(words1, n1);
    simhash2 = simhash(words2, n2);
    simhash32_1 = simhash32(simhash1);
    simhash32_2 = simhash32(simhash2);
    printf("text1: %s\n", text1);
    printf("text2: %s\n", text2);
    printf("simhash1: %lld\n", simhash1);
    printf("simhash2: %lld\n", simhash2);
    printf("simhash32_1: %lld\n", simhash32_1);
    printf("simhash32_2: %lld\n", simhash32_2);
    if (simhash32_1 == simhash32_2) {
        printf("text1 and text2 are similar.\n");
    } else {
        printf("text1 and text2 are not similar.\n");
    }
    return 0;
}

需要注意的是，上述代码中的分词、哈希算法和权重计算都需要根据具体的应用场景进行优化。同时，Simhash算法也有很多变体和改进，需要根据实际情况选择合适的算法。