What's the best hash function for a hex string?

Question

I'm looking to encode a set of hexadecimal values stored in strings using a hash function. Since the hex ''alphabet'' is composed of only 16 letters, what would be the best hash algorithm with the least amount of collisions?

Answer 1

Bit of a too general question, as you left out any constraints on the hash function, and/or what you're going to do with the hashes. (On a side note, hashing isn't an encoding)

That being said, having an alphabet of 16 letters, you need 4 bit to store each (i.e. you could build a XOR sum over each two letters crammed into a single byte, to get an 8-bit hash.
Of course, that can be extended to any other word length, too (but you left out too much information)

for instance like this:

uint8_t
hexhash(const char *str)
{
        uint8_t res = 0;
        while (*str && *(str+1)) {
                res ^= (fromchar(*str) << 4) | fromchar(*(str+1));
                str += 2; //EDIT: forgot this in my original reply
        }
        return res;
}

(where 'fromchar' is a function to return 0 for '0', 1 for '1', ..., 15 for 'f')