#include <ctype.h> #include "utils/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: