Author: Gerd Isenberg
Date: 01:42:38 09/21/04
Go up one level in this thread
On September 21, 2004 at 02:05:08, Tony Werten wrote:
<snip>
>>I have different code for white and black, but I have *never* liked it. It's
>>ugly and I will eventually get rid of it.
>
>Pawn are still a problem I think, since the solution is not much nicer:
>
>( assuming the compiler understands the a negative shl is a shr )
One possible solution is using a generalized branchless shift:
http://www.azillionmonkeys.com/qed/asmexample.html
---------------------------------------------------------------------
8. Generalized shift (32-bit)
unsigned long gensh(unsigned long v, int x) {
int a, b;
a = (v << x) & -(((unsigned int)x) < 32);
x = -x;
b = (v >> x) & -(((unsigned int)x) < 32);
return a|b;
}
and asssembly
---------------------------------------------------------------------
for bitboards:
BitBoard gensh(BitBoard v, int x) {
int a, b;
a = (v << x) & -(((unsigned int)x) < 64);
x = -x;
b = (v >> x) & -(((unsigned int)x) < 64);
return a|b;
}
Another nice C++ solution for compile time constants is to use integer templates
like:
template<int color> BitBoard pushPawn (BitBoard pawns)
{
if ( color ) return pawns >> 8;
return pawns << 8;
}
Gerd
>
>BLACK=0
>WHITE=1
>
>int LeftSideAttack={-9,7};
>int RightSideAttack={-7,9};
>
>pieces=Pieces[stm][pawn];
>
>pawnattacks=(pieces & NOT_FILE_A)<<LeftSideAttack[stm]
> |(pieces & NOT_FILE_H)<<RightSideAttack[stm])
>
>AttackedPieces=pawnattacks & Pieces[stm^1][all]
>
>Hmm, actually writing it down, makes it less messier than it was in my head.
>That is, if the first assumption is met.
>
>Tony
>
>
>
>
>>
>>Bas.
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