Author: Gerd Isenberg
Date: 13:58:07 02/23/06
Go up one level in this thread
On February 23, 2006 at 16:28:20, Dann Corbit wrote:
>On February 23, 2006 at 16:08:12, Gerd Isenberg wrote:
>
>>On February 23, 2006 at 15:49:46, Dann Corbit wrote:
>>
>>>On February 23, 2006 at 15:29:17, Gerd Isenberg wrote:
>>>
>>>>Sounds very interesting, Dann. Can you elaborate a bit more about the idea?
>>>>Do you mean a kind of rotated lookup with 7-bit distinct white/black occupied
>>>>states?
>>>
>>>For any given ray there are at most 128 possible states (7 bits, as you say)
>>>because we do not need to count the square on which we are standing.
>>>
>>>So, obvoiusly, a switch() with 128 labels can account for every possibility.
>>>Suppose you have a diagonal slider at e5.
>>>The labels will look like:
>>>
>>>switch case(masked_diagonal)
>>>case a1:
>>>/* do stuff */
>>>break;
>>>case a1b2:
>>>/* do stuff */
>>>break;
>>>
>>>...
>>>
>>>case h8:
>>>/* do stuff */
>>>break;
>>>
>>>default:
>>>assert(false);
>>>}
>>>
>>>Since you have at your disposal bitboards for every piece and for all white and
>>>for all black and for all chessmen of any color, you can precompute
>>>*everything*.
>>>
>>>The best thing about it (I think) is that the need for rotating the bitboards
>>>goes away completely (though your generator that computes the sliders is much
>>>easier if you use rotated bitboards for that). But the generator is not part of
>>>your chess program. It just writes four functions for each square on the
>>>chessboard.
>>>
>>>So (for instance) you might have a file called e5.cpp.
>>>
>>>Inside of e5.cpp, we will find methods e5p() {diagonal, e5 with + slope},
>>>e5m(){diagonal, e5 with - slope}, e5v() {e5 vertical} and e5h() {e5 horizontal}
>>>[Well, may as well toss in e5n() {e5 knights} etc.]
>>>
>>>There are (of course) other ways to organize it, and 64 files is a lot of files,
>>>but it's not like you have to do a lot of writing, since you write a single
>>>program to generate them.
>>>
>>>Is it clear?
>>
>>No sorry, not exactly - or better not at all.
>>
>>How are those generated functions called during movegeneration inside the chess
>>program? Do you have arrays of functions pointers indexed by squares and what
>>else?
>>
>>May be i am to biased with the De Bruijn stuff ;-)
>
>Calling the function returns a structure.
>The structure will contain:
>1. A list of captures + pawn promotions
>2. A list of non-captures
>Calling the function updates an array of structures that increments counts of
>sqare attacks by piece types, and square shadow attacks by piece type (a shadow
>attack is a pin or a battery due to a ray attack with one object in the way).
>It also computes half shadow attacks (which are pins or batterys with two
>chessmen in the way {of either color}).
>
>The operations are all precomputed, and so are branchless.
>For instance, if we have this board:
>[D]K7/6p1/8/4B3/8/2P5/8/7k w - -
>we will have (among other things) ...
>
>Game.c3.WhiteBishopAttacks++; /* Useful to know this chessman is not hung */
>Game.d4.WhiteBishopAttacks++; /* also a non-capture move will generate */
>Game.f6.WhiteBishopAttacks++; /* also a non-capture move will generate */
>Game.g7.WhiteBishopAttacks++; /* also a capture move will generate */
>
>Game.a1.WhiteBishopShadows++; /* Useful for board control, pins and battery */
>Game.b2.WhiteBishopShadows++; /* Useful for board control, pins and battery */
>Game.h8.WhiteBishopShadows++; /* Useful for board control, pins and battery */
>
>So the precomputed stuff will show us not only which captures we can make, but
>also if the piece we want to capture is defended, how many defenders there are,
>and what type of defenders they are. For empty squares, we can know if it is
>pawn safe, ... king safe
I still don't get it. Do you have precalculated [128*128] arrays?
How does the white/black occupied information interact with the functions.
Why functions and mot an array of structs?
Thanks for your patience.
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