哈希算法MD5实现 c语言并给代码注释

好的，我知道了。以下是哈希算法MD5的C语言代码注释：

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

#define LEFTROTATE(x, c) (((x) << (c)) | ((x) >> (32 - (c))))

// 将输入字符串转换为二进制表示，并进行填充
// 对于较短的输入，填充到长度为 448 mod 512
// 然后在末尾添加一个长度为 64 位的二进制数，表示输入长度
uint8_t *md5(const char *message) {
    // 消息填充，以及长度记录
    size_t initial_len = strlen(message);
    uint8_t *msg = calloc(initial_len + 64, 1);
    memcpy(msg, message, initial_len);
    msg[initial_len] = 128;
    uint64_t bits_len = 8 * initial_len;
    memcpy(msg + initial_len + 56, &bits_len, 8);

    // 初始化 MD 缓冲区
    uint32_t h0 = 0x67452301;
    uint32_t h1 = 0xEFCDAB89;
    uint32_t h2 = 0x98BADCFE;
    uint32_t h3 = 0x10325476;

    // 循环压缩每个 512 位的消息块
    for (int i = 0; i < initial_len + 64; i += 64) {
        uint32_t *w = (uint32_t *)(msg + i);

        uint32_t a = h0;
        uint32_t b = h1;
        uint32_t c = h2;
        uint32_t d = h3;

        // 进行 64 次操作
        for (int j = 0; j < 64; ++j) {
            uint32_t f, g;

            if (j < 16) {
                f = (b & c) | ((~b) & d);
                g = j;
            } else if (j < 32) {
                f = (d & b) | ((~d) & c);
                g = (5 * j + 1) % 16;
            } else if (j < 48) {
                f = b ^ c ^ d;
                g = (3 * j + 5) % 16;
            } else {
                f = c ^ (b | (~d));
                g = (7 * j) % 16;
            }

            uint32_t temp = d;
            d = c;
            c = b;
            b += LEFTROTATE((a + f + k[j] + w[g]), r[j]);
            a = temp;
        }

        h0 += a;
        h1 += b;
        h2 += c;
        h3 += d;
    }

    // 将缓冲区拼接为最终的哈希值
    uint8_t *result = calloc(16, 1);
    memcpy(result, &h0, 4);
    memcpy(result + 4, &h1, 4);
    memcpy(result + 8, &h2, 4);
    memcpy(result + 12, &h3, 4);
    free(msg);
    return result;
}

int main() {
    char *message = "hello world";
    uint8_t *hash = md5(message);
    for (int i = 0; i < 16; ++i) {
        printf("%02x", hash[i]);
    }
    printf("\n");
    free(hash);
    return 0;
}

以上是哈希算法MD5的C语言实现代码，并进行了注释，希望能够帮助你。