antirez hashing function #1

README

Description of AHF1 algorithm:

Initialize the four bytes H[0], H[1], H[2], H[3] to respectively 8D CA 2E 35
Initialize IDX to 0

For each byte B in the string to hash:

    TARGET = (B XOR H[IDX]) MOD 4

    H[TARGET] = H[TARGET] XOR B

    ROTATION = B MOD 16

    Use H0, H1, H2, H3 to compose a 32 bit sequence where H0 is the least significant
    byte and H3 is the most significant byte, then rotate the sequence by "ROTATION"
    bits using a circular shifting. Finally Set H0, H1, H2, H3 to the new bits.

    IDX = IDX+1 MOD 4

The output of the hash function is the 32 bit integer composed by H0, H1, H2, H3 where
H0 is the LSB and H3 the MSB.

ahf1.c

#include <stdint.h>
#include <sys/types.h>

/* antirez hash function one (AHF1)
 *
 * FIXME: make it byte ordering agnostic.
 *
 * TEST VECTOR:
 * "123456789" => 2934016909
 * "Message Digest" => 1454815842
 */
uint32_t ahf1(unsigned char *s, size_t len) {
    uint32_t hash;
    unsigned char *h = (unsigned char*) &hash;
    int idx = 0;

    h[0] = 0x8D;
    h[1] = 0xCA;
    h[2] = 0x2E;
    h[3] = 0x35;
    while(len) {
        int target = ((*s) ^ h[idx]) & 3;
        int rot = *s & 0x1F;

        h[target] ^= *s; /* step 1: XOR with target byte. */
        hash = (hash << rot) | (hash >> (32-rot)); /* step 2: Circular shifting. */
        len--;
        s++;
        idx = (idx+1) & 3;
    }
    return hash;
}


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

int main(void) {
    printf("%lu\n", (unsigned long) ahf1((unsigned char*)"123456789",9));
    return 0;
}