Author: Sune Fischer
Date: 01:38:25 06/26/02
Go up one level in this thread
On June 26, 2002 at 02:02:28, Bruce Moreland wrote:
>On June 25, 2002 at 05:26:34, Sune Fischer wrote:
>
>>On June 24, 2002 at 20:33:32, Russell Reagan wrote:
>>
>>>I am not an experienced bitboard user. I've been thinking about trying them out
>>>just to see how they work in comparison with my current 0x88 implementation. Is
>>>there any potential problem in mixing the two approaches? One problem that I can
>>>see would be that if you have an index for a bitboard, it's not going to index
>>>into the same square in your 0x88 array. I suppose the only real reason to keep
>>>0x88 would be for efficient edge detection. Do bitboards offer a solution to
>>>edge detection? Or do they even need edge detection when using bitboards (ex.
>>>using the BSF asm instuction would seem to avoid edge detection altogheter)?
>>>
>>>Thanks,
>>>Russell
>>
>>For edge detection you can do this:
>>
>>if (((uint64)1<<square)&0xFF818181818181FF)
>> ...
>>
>>it will tell you when you are on the first and last file or rank.
>>I use that in my SEE to raytrace behind the attacking piece, something like
>>
>>while (!(((uint64)1<<square)&0xFF818181818181FF)) {
>> square+=direction;
>> if (there-is-an-attacker-on-square)
>> add-it-to-the-list-of-attackers
>>}
>>
>
>That shift has to be lots of fun for the processor.
That is why I really use a Mask[square] table, but for the sake of clarity... :)
Anyway I changed it to a macro, so now I can quickly test which is faster, and
it seems the Mask[] lookup is faster, for the moment.
-S.
>bruce
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