Author: Frank Phillips
Date: 10:25:09 09/22/03
Go up one level in this thread
On September 22, 2003 at 09:50:33, Sune Fischer wrote:
>On September 22, 2003 at 09:10:55, Vincent Diepeveen wrote:
>>
>>And 2.2 times slower even with inline assembly.
>>
>>Not to mention what happens when you don't have assembly available.
>>
>>For everyone who does *not* like to have inline assembly, do *not* use
>>bitboards.
>
>Actually, I just tested a simple C version against the assembler version
>yesterday, and the C version came out faster on my "frenzee mark".
>with assembler : 1072
>no assembler : 1092 (!)
>
>Quite a big difference so I was somewhat surprized.
>The C version is "cheating" by using a big table though, could be bad in the
>long run if the program grows.
>
>The C version:
>
>inline FirstOneClear(BitBoard &bb) { // preconditioned by bb!=0
> BitBoard b = bb & -bb;
>
> bb ^= b;
> if (b<<48)
> return (first_one[b]);
> if (b<<32)
> return (first_one[b>>16]+16);
> if (b<<16)
> return (first_one[b>>32]+32);
> return (first_one[b>>48]+48);
>}
>
>The Assembler version:
>
>inline FirstOneClear(BitBoard &bb) {
> __asm
> {
> xor edx, edx
> mov ebx, [bb]
> xor eax, eax
> inc edx
> bsf ecx, [ebx]
> jnz found
> bsf ecx, [ebx+4]
> lea ebx, [ebx+4]
> xor eax, 32
> found:
> shl edx, cl
> xor eax, ecx
> xor [ebx], edx
> }
>}
>
>the assembler returns 63-square, so it must be flipped.
>
>Maybe faster versions of both even exists :)
>
>-S.
Is this an Athlon? My _program_ is faster with the lookup table approach on an
Athlon - although I do not used rotated BitBoards for move generation, which
should make the difference bigger I guess.
Frank
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