Code:unsigned int hashpjw(const void *key) { const char *ptr; unsigned int val; val=0; ptr=key; while (*ptr != '\0') { unsigned int tmp; val = (val << 4) + (*ptr); ;i dont understand this if (tmp = (val & 0xf0000000) ) { val = val ^ (tmp >> 24); val = val ^ tmp; } ptr++; } return nevermind; }
val i left-shifted 4 places then the character at ptr is added. The problem is that val is uninitialized, and on the row below (val & 0xf0000000) is assigned to tmp not compared. Where did you find this?
FWIW some hashing functions seemingly works by magic.
Last edited by Subsonics; 04-12-2012 at 04:42 AM.
Actually, forget what I just said, val is assigned 0 at the row below the declaration. And the test works in a similar manner as: if( (c = getchar()) == EOF ). Still, answering why a particular hashing function performs well (as in produces an even distribution) can be perplexing. I have been using djb2 for example which is a simple string hashing function but produces very even distribution.
