Author: Dann Corbit
Date: 14:47:32 01/13/05
Go up one level in this thread
On January 13, 2005 at 17:43:43, Dann Corbit wrote:
>On January 13, 2005 at 17:18:46, Eric Oldre wrote:
>
>>I have a rotated bitboard based engine. (Latista)
>>
>>My board representation looks like the following.
>>
>>//piece types
>>typedef enum {
>> PIECEEMPTY,
>> PIECEWPAWN, PIECEWKNIGHT, PIECEWBISHOP, PIECEWROOK, PIECEWQUEEN, PIECEWKING,
>> PIECEBPAWN, PIECEBKNIGHT, PIECEBBISHOP, PIECEBROOK, PIECEBQUEEN, PIECEBKING,
>> };
>>
>>
>>struct chessboard {
>>public:
>> /* other stuff */
>>
>> U64 bb_pieces[13]; //bitboards of piece locations
>
>??13??
>
>>
>>};
>>
>>I noticed while reading the crafty source that Crafty uses a structure more like
>>this.
>>
>>struct chessboard {
>>public:
>> /* other stuff */
>> //bitboards of piece locations
>> U64 wPawns;
>> U64 wKnights;
>> U64 wBishops;
>> U64 wRooks;
>> U64 wQueens;
>> U64 wKings;
>>
>> U64 bPawns;
>> U64 bKnights;
>> U64 bBishops;
>> U64 bRooks;
>> U64 bQueens;
>> U64 bKings;
>>};
>>
>>so Prof. Hyatt can then use the following
>>
>>board->wPawns;
>>instead of the equiv. in my engine
>>board->bb_pieces[PIECEWPAWN];
>>
>>I've also noticed that Crafty is much faster than my engine, Although I'm sure
>>that there are MANY MANY reasons for Crafty's better speed, I'm considering
>>trying a switch to a board format similar to Crafty's.
>>
>>I know you can't perfectly predict what type of gain/loss I'd get, but I thought
>>I'd ask if anyone thought It might be worth it.
>>
>>Or maybe you can tell me that it shouldn't make much difference and I'll save
>>myself some time.
>>
>>Thanks for any advice you have,
>
>The separation by type is useful not only for move generation but also
>evaluation.
>
>Also, you can do things by exact types (e.g. white pawn moves are different from
>black pawn moves).
>For example:
>while (white_pawns_bitboard)
>{
>loc = get_and_clear_bit(white_pawns_bitboard);
>do_stuff_with_white_pawn_at_loc(loc);
>}
>
>Doesn't sound so great?
>
>Consider:
>loc = get_and_clear_bit(some_bitboard);
>switch(get_color(loc)) {
>case WHITE:
>switch (get_type(loc)) {
>case PAWN:
>do_pawn_stuff(loc, WHITE);
>case KNIGHT:
>do_knight_stuff(loc, WHITE);
>/* ... etc for each piece type */
>}
>
>break;
>case BLACK:
>/* like above for black pieces */
>break;
>}
>
>as you can see, all that switching and figuring out colors and types is not
>needed if you store by color and type.
>
>mispredicted branches are like dropping bricks on your toes.
Oops. Now I see what you are doing.
The difference is almost irrelevant. I doubt you will see any change in speed
at all. Possibly, the array lookup might be some miniscule bit slower than a
direct element, but I think your notation might even be more convenient.
I would not change that bit of your program. Speed difference is from something
else.
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