将MD5结果转换为C中的整数 [英] Converting MD5 result into an integer in C

问题描述

我的目标是使用MD5结果的结果来索引哈希表.我想对其执行模数运算，以在表中找到合适的插槽.我尝试将其强制转换为无符号的long long类型.当我打印结果时，对于相同的MD5哈希，每次都会得到一个不同的数字. MD5哈希最初是一个无符号的char *.有人可以告诉我我在做什么错吗?

My goal is to use the result of an MD5 result to index a hash table. I want to perform a Modulo operation on it to find the appropriate slot in the table. I have tried casting it as an unsigned long long type. When I printed the result, I got a different number every time for the same MD5 hash. The MD5 hash is initially an unsigned char *. Can someone tell me what I am doing wrong?

这是我的功能:

int get_fp_slot(unsigned char * fingerprint, int size)
{
return (unsigned long long)fingerprint % size;
}

推荐答案

MD5哈希是一个128位数字.因此，为了获得最佳性能，您可能应该保留所有128位.

An MD5 hash is a 128 bit number. So for best performance you should probably keep all 128 bits.

鉴于您的函数将128位哈希作为字符串，因此您需要将该字符串解析为4个整数的序列.您的字符串可能看起来像这样:

Given that your function takes the 128 bit hash as a character string, you need to parse that string into a series of 4 integers. Your string probably looks something like this:

79054025255fb1a26e4bc422aef54eb4

这是一个32字节的十六进制字符串.如果是这样，您可以像这样提取二进制版本:

That is a 32 byte hexadecimal string. If so, you extract the binary version like this:

int v1, v2, v3, v4;
sscanf( &fingerprint[0], "%x", &v1 );
sscanf( &fingerprint[8], "%x", &v2 );
sscanf( &fingerprint[16], "%x", &v3 );
sscanf( &fingerprint[24], "%x", &v4 );

您现在要做的事情实际上取决于您希望哈希值有多好.如果您确实需要使用32位数字，则只需对所有这些数字进行XOR:

What you do now really depends on how good you want your hash to be. If you really need to use a 32 bit number then just XOR all those numbers together:

int hash = v1 ^ v2 ^ v3 ^v4;

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