Author: Tord Romstad
Date: 07:04:01 12/03/03
Go up one level in this thread
On December 03, 2003 at 06:25:35, Tim Foden wrote:
>On December 01, 2003 at 06:57:13, Tord Romstad wrote:
>
>>void compute_attacks() {
>> int i, colour, *p, sq, tosq, piece;
>> uint16 mask, *attacks;
>>
>> for(p=(int *)(Attacks+64), i=0; i<8; i++, p+=8)
>> *p = *(p+1) = *(p+2) = *(p+3) = 0;
>> for(p=(int *)(XAttacks+64), i=0; i<8; i++, p+=8)
>> *p = *(p+1) = *(p+2) = *(p+3) = 0;
>>
>> attacks = Attacks;
>> for(i=0, colour=Colour; i<2; i++, colour^=1) {
>> for(sq=Pieces[colour].next; sq!=255; sq=Pieces[sq].next) {
>> for(p = &(PieceDirs[Board[sq]][0]); *p; p++) {
>> piece = Board[sq]; mask = PieceMasks[piece];
>> tosq = sq + *p;
>> while(1) {
>> attacks[tosq] |= mask; attacks[tosq]++;
>> if(!(Abilities[piece] & SLIDING) || Board[tosq] == OUTSIDE
>> || Board[tosq] == WK || Board[tosq] == BK) break;
>> if(Board[tosq]) {
>> if(PieceColour(Board[tosq]) == PieceColour(piece) &&
>> (DirectionType[*p] & Abilities[Board[tosq]])) {
>> /* X-ray attack. The &0xFF at the next time masks off
>> * the direct attack bits. */
>> mask = PieceMasks[max(piece, Board[tosq])] & 0xFF;
>> piece = Board[tosq]; }
>> else break; }
>> tosq += *p; }}}
>> attacks = XAttacks; }}
>>
>>From the initial position, I compute the attack tables about a million
>>times per second with this code. From WAC1, the rate drops to about
>>700,000 times per second. The high nodes/second count of Rebel (which
>>has similar tables) makes me believe that it is possible to do this
>>many times faster.
>>
>>Tord
>
>Hi Tord,
Hi Tim, and thanks for the comments!
>I had a brief look at this code... here are my comments: :)
>
>1. It may be slightly faster to put the "attacks[tosq] =" line after the "if"
>that is below it. Try it and see.
Faster, perhaps, but it would give wrong results. No bits for non-sliding
pieces would ever be set.
>2. I feel that it will be slightly more common, and will be quicker to test,
>whether the tosq is out of bounds, than to check for sliders. I would therefore
>try putting the Board[tosq] == OUTSIDE before the test for a slider.
You're probably right about this one -- I'll give it a try.
>3. The explicit tests for the Board[tosq] == WK and Board[tosq] == BK seem
>strange. This will surely be handled by the slider case anyway, so should never
>be true (unless for some reason you have kings as being sliding pieces).
No, the tests for Board[tosq]==WK and Board[tosq]==BK are really necessary.
It is not handled by the slider case, because Abilities[piece]&SLIDING
tests whether the piece that attacks tosq is sliding, not whether the
king is sliding.
The point of the test is to avoid generating x-ray attacks through a king.
If there is a white bishop on d3 and a white pawn on e4, The bishop should
be counted as one of the white attackers of the square f5. But if the
pawn on e4 is replaced by a white king, the bishop on d3 is no longer
attacking f5. This is the point of the tests.
>4. Is PieceColour(piece) the same as colour? If so you can replace
>PieceColour(piece) with colour.
You're right, of course. How stupid of me to overlook this obvious
improvement.
>5. DirectionType[*p] is a constant for each direction. It may be faster to look
>this up once rather than many times.
Perhaps. I thought the compiler should be smart enough to do this for me,
but perhaps it is worth trying.
>6. Taking constants outside the loops is generally a good idea. It may be
>better to reformulate the code so that piece and mask don't change, and use
>piece2 and mask2 inside the while loop. I know it isn't quite clear how to do
>this, but it may be possible. I.E. don't start the while loop at all for the
>non-sliding cases.
Yes, perhaps I could make something like this work (although I'm afraid
it would make the code more complicated). I'll have a look at it.
>Well, thats all for now. I hope some of it actaully helps! :)
I'm sure it does -- thanks a lot for your help!
Tord
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