hash.c

#include <stdio.h>
#include "hash.h"

uint64_t AwareHash(unsigned char* data, uint64_t n,
        uint64_t hash, uint64_t scale, uint64_t hardener) {

	while (n) {
		hash *= scale;
		hash += *data++;
		n--;
	}
	return hash ^ hardener;
}


uint64_t AwareHash_debug(unsigned char* data, uint64_t n,
        uint64_t hash, uint64_t scale, uint64_t hardener) {

	while (n) {
        fprintf(stderr, "    %lu %lu %lu %u\n", n, hash, scale, *data);
		hash *= scale;
		hash += *data++;
		n--;
        fprintf(stderr, "        internal %lu\n", hash);
	}
	return hash ^ hardener;
}

/*
 * mangle
 */
void mangle(const unsigned char* key, unsigned char* ret_key,
		int nbytes) {
	unsigned long long new_key = 0;
	int i;
	for (i=0; i<nbytes; ++i) {
		new_key |= key[nbytes-i-1] << (i * 8);
	}
	new_key = (new_key * 2083697005) & (0xffffffff);
	for (i=0; i<nbytes; ++i) {
		ret_key[i] = (new_key >> (i * 8)) & 0xff;
	}
}

uint64_t seed = 0;
uint64_t GenHashSeed(int index) {
    /*
    if (index == 0) {
        srand(0);
    }
    */
    if (seed == 0) {
        seed = rand();
    }
    uint64_t x, y = seed + index;
    mangle((const unsigned char*)&y, (unsigned char*)&x, 8);
    return AwareHash((uint8_t*)&y, 8, 388650253, 388650319, 1176845762);
}

int is_prime(int num) {
    int i;
    for (i=2; i<num; i++) {
        if ((num % i) == 0) {
            break;
        }
    }
    if (i == num) {
        return 1;
    }
    return 0;
}

int calc_next_prime(int num) {
    while (!is_prime(num)) {
        num++;
    }
    return num;
}