Author: Russell Reagan
Date: 09:11:20 01/21/03
Go up one level in this thread
As far as I can tell, it boils down to this. Which of these will be faster?
Let's define "version 1" to be computing attacks using rotated bitboards, and
"version 2" using the fill routines (shown below). For this example, let's
compute rook attacks. Computing rook attacks is a few table lookups, a few
shifts, and a couple of ANDs.
Do you think version 2 can compare to that? I'm doubtful. Table lookups are
"free" basically, and you are doing WAY more shifting and bitwise operations in
version 2. The only way version 2 could keep up is if you have multiple rooks
that you want to compute attacks for. This doesn't help for things like move
generation, but it would if you were calculating the attacks for one color. Even
then, it only helps if you have more than one rook on the board.
I'm not sure if the parallel speed up would be faster than doing two attack
generations using rotated bitboards. The only place this might be a big gain is
in generating pawn attacks since there can be up to eight of them, but I don't
think generating pawn attacks are a big bottleneck for most people.
// Version 2
// To compute rook attacks, you have to call ALL FOUR of these. It will compute
// attacks for any number of rooks on the board, but usually there will only
// be two, so this will have to be twice as fast as Version 1, which is
// a stretch.
Bitboard FillRightBlocked (Bitboard Source, Bitboard Clear)
{
Clear &= NotFileA;
Source |= Clear & (Source << 1);
Clear &= Clear << 1;
Source |= Clear & (Source << 2);
Clear &= Clear << 2;
Source |= Clear & (Source << 4);
return Source;
}
Bitboard FillLeftBlocked (Bitboard Source, Bitboard Clear)
{
Clear &= NotFileH;
Source |= Clear & (Source >> 1);
Clear &= Clear >> 1;
Source |= Clear & (Source >> 2);
Clear &= Clear >> 2;
Source |= Clear & (Source >> 4);
return Source;
}
Bitboard FillUpBlocked (Bitboard Source, Bitboard Clear)
{
Source |= Clear & (Source << 8);
Clear &= Clear << 8;
Source |= Clear & (Source << 16);
Clear &= Clear << 16;
Source |= Clear & (Source << 32);
return Source;
}
Bitboard FillDownBlocked (Bitboard Source, Bitboard Clear)
{
Source |= Clear & (Source >> 8);
Clear &= Clear >> 8;
Source |= Clear & (Source >> 16);
Clear &= Clear >> 16;
Source |= Clear >> 32;
return Source;
}
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