CocoaDev

here’s some hash functions for those who like to optimize there core foundation dictionaries. These are C versions of the C++ versions post here -> http://www.partow.net/programming/hashfunctions/

When you supply the hash hook function for CFDictionaryHashCallBack you have to cast the function correctly (e.g. keyCallbacks.hash = (CFHashCode (*)(const void *))ELFHash;)

C Hash Functions:

unsigned int RSHash(char str) { unsigned int a = 63689, b = 378551, hash = 0, i, length = strlen(str); for(i = 0; i < length; i++) {hash = hasha+str[i]; a = a*b;} return (hash & 0x7FFFFFFF); }

unsigned int JSHash(char *str) { unsigned int hash = 1315423911, i, length = strlen(str); for(i = 0; i < length; i++) hash ^= ((hash « 5) + str[i] + (hash » 2)); return (hash & 0x7FFFFFFF); }

unsigned int PJWHash(char *str) { unsigned int i, length = strlen(str); unsigned int BitsInUnignedInt = (unsigned int)(sizeof(unsigned int) * 8); unsigned int ThreeQuarters = (unsigned int)((BitsInUnignedInt * 3) / 4); unsigned int OneEighth = (unsigned int)(BitsInUnignedInt / 8); unsigned int HighBits = (unsigned int)(0xFFFFFFFF) « (BitsInUnignedInt - OneEighth); unsigned int hash = 0; unsigned int test = 0;

for(i = 0; i < length; i++) {
    hash = (hash << OneEighth) + str[i];
    if((test = hash & HighBits)  != 0) hash = (( hash ^ (test >> ThreeQuarters)) & (~HighBits));
}
return (hash & 0x7FFFFFFF); }

unsigned int ELFHash(char *str) { unsigned int hash = 0, x = 0, i, length = strlen(str); for(i = 0; i < length; i++) { hash = (hash « 4) + str[i]; if((x = hash & 0xF0000000L) != 0) {hash ^= (x » 24); hash &= ~x;} } return (hash & 0x7FFFFFFF); }

unsigned int BKDRHash(char str) { unsigned int seed = 131, hash = 0, i, length = strlen(str); for(i = 0; i < length; i++) hash = (hashseed)+str[i]; return (hash & 0x7FFFFFFF); }

unsigned int SDBMHash(char *str) { unsigned int hash = 0, i, length = strlen(str); for(i = 0; i < length; i++) hash = str[i] + (hash « 6) + (hash « 16) - hash; return (hash & 0x7FFFFFFF); }

unsigned int DJBHash(char *str) { unsigned int hash = 5381, i, length = strlen(str); for(i = 0; i < length; i++) hash = ((hash « 5) + hash) + str[i]; return (hash & 0x7FFFFFFF); }

–zootbobbalu

Very nice indeed, but how and why do I use them?