Author: Dann Corbit
Date: 10:50:14 03/04/06
Go up one level in this thread
On March 04, 2006 at 13:47:50, Dann Corbit wrote:
>On March 04, 2006 at 02:46:22, Gerd Isenberg wrote:
>
>>>OK. So you make an array of 128 function pointers then, and do this:
>>>
>>>status = method[hashval(BB)]();
>>
>>Yes, if you like, you can do either switch with a contiguous range as well.
>>But to get pure attacksets, there are no function pointers at all, but pointers
>>to bitboards.
>>
>>>
>>>PGO seems to take a lot of the sting out of missed branch predictions, but of
>>>course there will always be some.
>>
>>It would be interesting to see some pseudocode what your /* Do Stuff */ in the
>>cases does, to implement a kind of "ray-base" e.g. with the position you
>>mentioned recently. If you are interested in a1-h8 related properties of let say
>>square g7.
>>
>>[D]7k/3n2q1/5p2/8/6N1/2Q5/1B6/Q1K5 w - -
>
>There is probably a lot less magic in my stuff than you might imagine.
>
>First of all, I have direct attack bitmaps, shadow bitmaps, and half-pin bitmaps
>(I tried quarter-pin, but so far they seem to be too expensive for the payback,
>but half pin are clearly worthwhile). For this position, half pin is enough.
>Quarter pin positions are very rare.
>
>Anyway, the interesting guy is the pawn at f6. When I go to my switch, I will
>have precalcuated stuff against the full bitmap and also white and black, as
>well as piece.
>
>The upshot is that I have for every square on the board a list of attackers by
>type and by type of attack (direct, x-ray, half-pin). So let's consider the
>pawn. He has:
>
>white attackers black attackers(defenders)
>pawn direct(0) pawn direct(0) {no such thing as indirect for P}
>knight direct(1) knight direct(1) {no such thing as indirect for N}
>bishop direct(0) bishop direct(0)
>bishop x-ray(1) bishop x-ray(0)
>bishop half(0) bishop half(0)
>rook direct(0) rook direct(0)
>rook x-ray(0) rook x-ray(0)
>rook half(0) rook half(0)
>queen direct(1) queen direct(1)
>queen x-ray(0) queen x-ray(0)
>queen half(1) queen half(0)
Forgot to list the king attacks (both 0).
I consider a pawn attack to be the strongest attack and a king attack is the
weakest.
>In addition, we know that black is upside down on the pin, that the pinned piece
>is a queen and that the shadow pinned piece is a king (type of piece that is
>BEHIND the pinned piece is crucial and actually changes my pin type).
>
>My makemove actually updates these counts* (so movegen suffers a bit and will
>never compete with the fastest). As a side point, it makes a legal only move
>generator a snap.
>
>[*] The function pointers I was referring to are the things that:
>1. Remove the influence of the piece from the board (imagine picking it up)
>2. Add the new influence of the piece to the board (imagine putting it down)
>
>Besides helping out the evaluation a great deal, it is also stupendously helpful
>for move ordering. You can tell at a glance from the information presented that
>the queen's pawn capture is winning (makemove alone does not know it, but
>evaluation does without search).
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