Author: Tim Foden
Date: 14:56:52 07/14/03
Go up one level in this thread
On July 14, 2003 at 17:36:52, Sune Fischer wrote:
>On July 14, 2003 at 17:15:50, Bas Hamstra wrote:
>
>>Hi Gerd,
>>
>>A while ago, in Leiden, Frans mentioned you had a trick to reduce the rotated bb
>>lookup tables by a factor 2, without further disadvantages. It had something to
>>do with the edges of the board, some "ray-states" you can ignore. I didn't
>>understand his short explanation back then. Could you explain?
>>
>>Best regards,
>>Bas.
>
>It's quite simple; the state of the attack rank (or file) doesn't depend on the
>outermost squares/bits. Those squares are attacked (or not) no matter if there
>is a piece standing there. So actually it is a factor 4 you save, because you
>need only 6 bit entries.
>
>There are other tricks you can do to compact them even more, but then more
>shifting is needed to unpack the information.
>
>I have written a sample move generator that uses this trick:
>http://www.geocities.com/ruleren/crbmg.zip
>
>-S.
Hi Sune,
In another (very, very, early) chess program I'm writing (very, very, slowly!) I
have a bb movegen and makemove, and incheck test, etc., that uses tables
totalling about 15.5KB. The actual sliding pieces lookup tables total about
6.5KB.
static BYTE s_patMoves[8][256]; // 2.00K [R/F][pattern]
static UINT64 s_extendVert[256]; // 2.00K [pattern]
static UINT64 s_extendHorz[256]; // 2.00K [pattern]
static const UINT64 s_rankMask[8]; // 0.06K [file]
static const UINT64 s_fileMask[8]; // 0.06K [rank]
static const UINT64 s_diagAMask[15]; // 0.12K [diagA]
static const UINT64 s_diagHMask[15]; // 0.12K [diagH]
Using the 6bit instead of 8bit trick this could be reduced by another 1.5KB.
Fun eh? I thought I'd try to be a bit more cache friendly in my newest prog. :)
It's currently only at the stage where I can do a perft, where it is about 75%
the speed of GLC, but I haven't optimised it at all really (Whereas I've been
optimising GLC for years now :)). In fect the pure movegen looks to be about
90% the speed of GLC.
Cheers, Tim.
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