djb2: This algorithm (k=33) was first reported by dan bernstein many years ago in comp.lang.c. another version of this algorithm (now favored by bernstein) uses xor: hash(i) = hash(i - 1) * 33 ^ str[i]; the magic of number 33 (why it works better than many other constants, prime or not) has never been adequately explained.

hash_djb2.c

/**
 * hash_djb2 - implementation of the djb2 algorithm
 * @str: string used to generate hash value
 *
 * Return: hash value
 */
unsigned long int hash_djb2(const unsigned char *str)
{
	unsigned long int hash;
	int c;

	hash = 5381;
	while ((c = *str++))
	{
		hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
	}
	return (hash);
}

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