Author: Gerd Isenberg
Date: 12:51:25 04/16/04
Go up one level in this thread
On April 16, 2004 at 06:14:25, Andreas Guettinger wrote:
>Could somebody recap how the final macros look like, all inlined?
>What bitboards are needed to use the macros?
>Is the overhead of maintaining the bitmaps worth it?
>Is it a speedup to 0x88? Do you think its faster than a for loop checking for
>blocked squares between x and y?
>
>regards
>Andy
Hi Andy,
actually i would suggest something like this, bitboard return, to additionally
check whether the popcount is zero or one, probably looking for xrays, pins and
remove checkers.
inline
BitBoard brq_path_clear(x88sqr gt, x88sqr ls, U64 BitBoard) {
return (isqBit(gt) - 2*isqBit(ls)) & path & all;
}
BitBoard bstyle_attack(x88sqr x, x88sqr y) {
int dir = direction0x88Diff[0x88+x-y]); // 256 sized lookup
if ( dir & isDiagonalDirection )
{
BitBoard path = pathOfDirection[dir];
if ( x > y ) return brq_path_clear(x, y, path);
return brq_path_clear(y, x, path);
}
return (BitBoard) -1;
}
Same for rooks, excecpt looking for straight rays.
This is cache friendly, has two conditional jumps and some computations.
Probably a 64*64 inbetween lookup with x and y is faster, but pollutes the cache
32KByte (+4/8/16Kbyte) a bit more.
One should try, saves some instructions and missed branches.
BitBoard bstyle_attack(square64 x, square64 y) {
int dir = direction[x][y]; // 4K char(short/int lookup
if ( dir & isDiagonalDirection )
return inBetween[x][y] & all; // 32K lookup
return (BitBoard) -1;
}
Or even faster and complete branchless with two proper initialized 32KByte
arrays (contains -1 for non common squares for diagonal and straight):
// returns all if non common diagonals
BitBoard bstyle_attack(square64 x, square64 y) {
return inBetweenButOnlyDiagonals[x][y] & all;
}
BitBoard rstyle_attack(square64 x, square64 y) {
return inBetweenButOnlyStraight[x][y] & all; // 32K lookup
}
Ok, a tiny loop looking on the board is not that bad and very resource friendly.
But you have up to two conditions (target square reached, occupied)per run. And
the number of runs depends on the distance (up to six runs) and whether you got
an early break. In best case with two adjacent squares it is faster.
So you may try it, it depends on so much "chaotical things" inside a concrete
chess program and of course on the target CPU, cache size etc...
Cheers,
Gerd
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