#include <ctype.h>

#include "hash.h"

/**
 * SDBM hashing algorithm:
 *
 * this algorithm was created for sdbm (a public-domain reimplementation of
 * ndbm) database library. it was found to do well in scrambling bits,
 * causing better distribution of the keys and fewer splits. it also happens
 * to be a good general hashing function with good distribution. the actual
 * function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
 * is the faster version used in gawk. [there is even a faster, duff-device
 * version] the magic constant 65599 was picked out of thin air while
 * experimenting with different constants, and turns out to be a prime. this
 * is one of the algorithms used in berkeley db (see sleepycat) and elsewhere. 
 */
unsigned long
sdbm(const unsigned char * str)
{
	unsigned long hash = 0;
	int c;

	while ((c = tolower(*str++)))
		hash = c + (hash << 6) + (hash << 16) - hash;

	return hash;
}

// vim: set ts=4 sw=4: