Author: Tony Werten
Date: 02:14:05 09/16/01
Go up one level in this thread
On September 15, 2001 at 20:32:38, Robert Hyatt wrote:
>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.
What do you think is the reason for this ? Is it because 64bit instruction need
more time or is it the thrashing of the cache ?
If I had a way getting the bitboard with more computational effort ( say 4-5
times ) but in total taking less than 2 Kb, would it be faster then ?
Tony
>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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