simhash算法c语言

以下是 simhash 算法的 C 语言实现示例：

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

#define MAX_NUM 1024
#define BITS_NUM 64

typedef unsigned long long uint64_t;

// 将字符串转换为 simhash 值
uint64_t simhash(char *s);

// 计算哈希值
uint64_t hash(char *s);

// 计算汉明距离
int hamming_distance(uint64_t x, uint64_t y);

int main() {
    char *s1 = "hello world";
    char *s2 = "hello wold";
    uint64_t simhash1 = simhash(s1);
    uint64_t simhash2 = simhash(s2);
    int distance = hamming_distance(simhash1, simhash2);
    printf("s1: %s\ns2: %s\nsimhash1: %llu\nsimhash2: %llu\ndistance: %d\n", s1, s2, simhash1, simhash2, distance);
    return 0;
}

uint64_t simhash(char *s) {
    // 计算特征向量
    int features[BITS_NUM] = {0};
    char *token = strtok(s, " ");
    while (token != NULL) {
        uint64_t h = hash(token);
        for (int i = 0; i < BITS_NUM; i++) {
            if ((h >> i) & 1) {
                features[i]++;
            } else {
                features[i]--;
            }
        }
        token = strtok(NULL, " ");
    }
    // 计算 simhash 值
    uint64_t simhash = 0;
    for (int i = 0; i < BITS_NUM; i++) {
        if (features[i] > 0) {
            simhash |= (1ull << i);
        }
    }
    return simhash;
}

uint64_t hash(char *s) {
    uint64_t h = 0;
    while (*s) {
        h = h * 131 + *s;
        s++;
    }
    return h;
}

int hamming_distance(uint64_t x, uint64_t y) {
    uint64_t z = x ^ y;
    int distance = 0;
    while (z) {
        distance++;
        z &= z - 1;
    }
    return distance;
}

代码中，simhash 函数计算字符串的 simhash 值，hash 函数计算字符串的哈希值，hamming_distance 函数计算两个 simhash 值的汉明距离。在 simhash 函数中，首先将字符串分词，计算每个词的哈希值，并根据哈希值的每一位更新特征向量，最后根据特征向量计算 simhash 值。