CToolBox/include/toolbox/hash.h

#ifndef HASH_H
#define HASH_H

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

__attribute__((access (read_only, 1), nonnull, pure))
uint64_t hash(const uint8_t* data, size_t size);

__attribute__((pure))
uint64_t uint64_hash(uint64_t key);

#if defined(HASH_IMP) || defined(IMPLEMENTATIONS)

/* Thomas Wang 64 bit mix hash function. */
uint64_t
uint64_hash(uint64_t key)
{
	key = (~key) + (key << 21); // key *= (1 << 21) - 1; key -= 1;
	key = key ^ (key >> 24);
	key = key + (key << 3) + (key << 8); // key *= 1 + (1 << 3) + (1 << 8)
	key = key ^ (key >> 14);
	key = key + (key << 2) + (key << 4); // key *= 1 + (1 << 2) + (1 << 4)
	key = key ^ (key >> 28);
	key = key + (key << 31); // key *= 1 + (1 << 31)
	return key;
}

uint64_t hash(const uint8_t* data, size_t size) {
	static uint8_t _primes_list[] = {
		3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59,
		61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127,
		131, 137, 139, 149, 151, 157, 163, 167, 173
	};
	static uint8_t _primes_list_size = 10;
	uint64_t max = UINT64_MAX >> 1;
	uint64_t ret = 1;
	uint8_t p = 0;
	size_t i = 0;
	byte_t b = 0;

	for ( i = 0; i < size; ++i ) {
		b = data[i];
		p = _primes_list[(i + b) % _primes_list_size];
		ret = (ret * (b * p)) % max;
	}

	return ret;
}

#endif /* HASH_IMP || IMPLEMENTATIONS */

#endif