Author: James Robertson
Date: 00:47:50 02/20/04
Go up one level in this thread
On February 19, 2004 at 19:24:10, Russell Reagan wrote:
>On February 19, 2004 at 18:16:17, Dann Corbit wrote:
>
>>You might want to examine here and below for an alternative pure C model that
>>seems to be just about the same speed:
>>http://www.talkchess.com/forums/1/message.html?349781
>
>I agree. The performance of the bsf/bsr instructions seems to depend greatly on
>what brand of CPU you are using. For instance, on a PIII, it is about ten times
>faster than it is on an Athlon. On the Athlon, the C versions are usually
>faster. I don't know about the P4.
>
>This is the one I usually use. Eugene Nalimov wrote it for the Itanium, but it
>runs about as fast or faster than most of the other routines I've tried on
>32-bit hardware. It requires one table lookup, but the table is only 256
>elements so it is cache friendly. The table data is just the first bit of the
>byte.
>
>int EugeneBitscan (Bitboard arg) {
> int result = 0;
>
> if (arg > 0xFFFFFFFF) {
> arg >>= 32;
> result = 32;
> }
>
> if (arg > 0xFFFF) {
> arg >>= 16;
> result += 16;
> }
>
> if (arg > 0xFF) {
> arg >>= 8;
> result += 8;
> }
>
> return result + table8[arg];
>}
>
>Have a look here for some others that I compared. There are comparisons for both
>32-bit and 64-bit hardware.
>
>http://chessprogramming.org/cccsearch/ccc.php?art_id=333679
Thanks a lot for this code. I'll look at it and see if it is better than what I
am doing now. C routines are always nicer than assembler equivalents if they
aren't too slow =)
James
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