Author: Ed Schröder
Date: 10:36:21 12/05/01
Go up one level in this thread
On December 05, 2001 at 13:04:49, Miguel A. Ballicora wrote: >On December 05, 2001 at 12:42:07, Ed Schröder wrote: > >>On December 05, 2001 at 06:46:07, Severi Salminen wrote: >> >>>>>#define color(target) (((info[target])>>3)&3) >>>>> >>>>> >>>>>my data.c file includes >>>>> >>>>>int info[64]; >>>>>int side; >>>>>int direction[64][64]; >>>>>int kingsquare[2]; >>>>>int pin[64]; >>>>> >>>> >>>>Perhaps the data types could be a reason for some microscopic effects. If the >>>>variable "side" is for instance of type "short", the compiler has to zero-extend >>>>the variable to word-size before indexing (because of the array access). >>> >>>But as you can see the variables are all ints. So no type conversions needed. I >>>believe there is just some stupid alignment thing happening or something and >>>that's why the program slows down a bit. I'd use side instead of color(sq) and >>>hopefully the speedup will show up later. >>> >>>Severi >> >> >>You could try to decrease the >> >>int direction[64][64]; >> >>by one, thus: >> >>int direction[63][64]; >> >>The result might be the compiler doesn't have to do an expensive multiply >>(*65) but is able to do a simple shift-left bits instruction (SHL 6) which >>shift left the bytes 6 times, thus a multiply by 64. > >I do not understand. Why would a compiler want to multiply by 65 in the first >place? Isn't 64 in both cases as determined by the second index? char xxx[0] defines 1 byte. char xxx[10] defines 11 bytes. etc. Ed >Regards, >Miguel > > > > >> >>Ed
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