Author: Robert Hyatt
Date: 17:32:38 09/15/01
Go up one level in this thread
On September 15, 2001 at 11:14:36, Sune Fischer wrote:
>Hi
>
>When I discovered that Crafty had some neat assembler rutines, I decided to test
>if they where faster than my humble rutines.
>I have up until now used a "raytracing" or boardtracing rutine to find the legal
>moves for the sliding pieces. And for the knights, pawns and king I simply check
>if the board has an allied piece on that square.
>It's a simple way of generating the legal moves.
>I still generate the attack bitboards to get the legal king moves though.
>
>I then tried to find all the moves directly from the bitboards by using one of
>Crafty's assember functions.
>This part of my program is only a minor part, but none the less it runs a full 8
>percent slower than my previous raytracing algorithm!!
Two points:
1. bitboards are a bit slower on 32 bit hardware. not a lot, but a bit.
On 64 bit hardware, this penalty disappears totally.
2. Remember that the majority of positions I generate moves for are
capture-only positions (q-search). Compare your raytracer to bitmaps for
generating _just_ captures. You will find an advantage to bitboards there.
>
>This is what I have now:
>
>void FindMovesQueen(..loads of pointers...)
>{
> int to_square;
> BITBOARD bb=(~allied.occupied) & allied.attack[board.id[from_square]];
>
> while (bb)
> {
> to_square=63-FirstOne(bb); // get a bit
> bb ^= mask[to_square]; // remove the bit
>
> movelist[++counter].from=from_square;
> movelist[counter].to=to_square;
> movelist[counter].piece=QUEEN;
> movelist[counter].capturedpiece=enemy.piece[board.id[to_square]];
> }
> return;
>}
>
>(movelist, counter, from_square etc. are passed in the argument)
>
>I know why it is slow too.
>First I have to form the bb, that's 2 bitboard operations.
>Then I need to run an algorithm, FirstOne from crafty, to find the first bit.
>Then I need to mask out that found bit.
>Both of these run several time pending on the while loop.
>Next is 4 lines I always have, no matter how I do it, so we can safely ignore
>those.
>The while loop is a conditional much like the if's I use when raytracing, so
>probably the if's and while almost cancel out.
>
>All in all I have added a lot of operations to my program, I am not surprized it
>is a lot slower. Given that the entire program suffer a slowdown by about 8.1
>percent, I estimate that this technique is more than twice as slow as the
>raytracing.
>The upside of things is that I reduce my code by about 1000 lines or so, but is
>this worth 8 percent in speed?
>I know the use of 64 bit processors will give a nice boost to this method and I
>probably can't expect anything like that for my tracing function, but frankly
>I'm not sure it would be enough to catch up.
>
>Am I mistaken, are the big boys doing something else?
>Is there an even faster way?
>I need to know :D :D
>
>Thanks,
>Sune
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