Author: Tony Werten
Date: 02:14:21 09/20/04
Go up one level in this thread
On September 20, 2004 at 04:53:46, Gerd Isenberg wrote:
>On September 20, 2004 at 03:16:41, Tony Werten wrote:
>
>>On September 20, 2004 at 03:06:54, Gerd Isenberg wrote:
>>
>>>On September 20, 2004 at 02:23:59, Tony Werten wrote:
>>>
>>>>It isn't doing things parallel like the sliders with Kogge Stone, but at least
>>>>it doesn't use those big arrays.
>>>>
>>>>const KNIGHTC3 // all attacks of a knight on square C3
>>>>
>>>>pieces=BITBOARD[stm][KNIGHT];
>>>>attacks=0;
>>>>while (pieces)
>>>>{
>>>> sq=bitscan_first_and_reset(pieces);
>>>> File(sq)>2 ? mask=NOT_FILE_AB:mask=NOT_FILE_GH;
>>>> if (sq>C3) attacks=(KNIGHTC3>>(sq-C3)) & mask;
>>> <<
>>
>>correct (when A1=0 and H8=63)
>
>Sorry for my nitpicking,
>but with other mapping sq>C3 doesn't make much sense ;-)
No problem. I wrote it down here, before I tested it. It's one of those easily
made errors with bitboards.
>
>>
>>>> else attacks|=(KNIGHTC3<<(C3-sq)) & mask;
>>> ?? >>
>>
>>correct. I'm mixing some things here. The |= is for all knight attacks, mostly
>>you only want =
>>
>>>>}
>>>>
>>>>For king is the same but on square B2. Since most of the time sq>C3 (or B2)
>>>>branch prediction should be OK.
>>>
>>>Even more for sq>=C3 (or b2).
>>
>>Yeah, that might do some 0.1 % better even :)
>
>I would say it goes under in some random noise.
>Probably same for direct lookup with a bitboard[64] array.
Well, it does free 1KB of cache :) My main point was to not use any lookuptables
at all, because I didn't like it( now that's a good reason)
>What about different routines for white and black knights/kings?
>Using f6(g7) for white and c3(b2) for black. During opening and middlegame
>branch prediction works even better ;-)
Besides lookuptables, I do not want to have black/white code either. ( With the
same good reason ) Unfortunately, those nasty pawns keep insisting on walking in
different directions.
Tony
>
>Gerd
>
>>
>>Tony
>>
>>>
>>>
>>>>
>>>>Tony
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