Author: Bas Hamstra
Date: 14:19:43 09/20/04
Go up one level in this thread
On September 20, 2004 at 05:14:21, Tony Werten wrote:
>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
I have different code for white and black, but I have *never* liked it. It's
ugly and I will eventually get rid of it.
Bas.
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