Author: Andrew Dados
Date: 17:25:51 02/10/00
Go up one level in this thread
On February 10, 2000 at 17:34:52, Tom Kerrigan wrote:
>There seems to be a huge pro-bitboard movement underway... But for those of us
>not jumping on the bandwagon, I have some thoughts.
>
>Let's say you have an array to represent the board:
>int board[64];
>
>If you make white pieces positive (i.e., pawn = 1, knight = 2) and black pieces
>negative, you can use the following macros:
>
>#define COLOR(x) (x < 0)
>#define TYPE(x) (x < 0 ? -x: x)
>
>I don't like the TYPE macro because it has a branch. So let's say you set bit #4
>if the piece is black. Then you can use these macros:
>
>#define COLOR(x) (x >> 3)
>#define TYPE(x) (x & 7)
>
>This seems pretty good, but I still have a minor complaint: a pawn = 1, so all
>the arrays that are indexed by piece type have to have an unused element at the
>beginning.
>
>You can set the pawn = 0, but then the empty square value has to be non-zero. On
>some proessors, this increases the time it takes to see if a square is empty.
>
>If you're using the 0x88 trick, you get two boards to play with, so the color of
>the piece on square x can be board[x] and the piece type can be board[x+8]. I
>think this is a pretty good solution, but it involves some extra memory
>accesses, not only when you're examining the board, but also when you're moving
>pieces around.
>
>If you have a piece struct, your board can be pointers to the structs:
>piece_struct *board[64];
>
>Then the color of the piece on square x is board[x]->color and the piece type is
>board[x]->type. I think this solution is pretty cool, but it involves some extra
>memory accesses. Plus, every time you want to check the piece type of square x,
>you have to make sure that board[x] isn't NULL. That's not cool.
>
>So... each method has its minor advantages and disadvantages. I can't really
>decide which I like more. What do other programmers do? Is there some really
>elegant solution that I'm missing? I hope so. :)
>
>-Tom
I define a structure:
{
piece: piecetype;
color: colortype;
index: byte (index into piece list);
dummy: byte
}
Although byte data size 'is evil' whole thing fits nicely into 32bit size size.
So 0x88 board is array[127] of dword data.
While you can easily combine 2 bytes into piececolor with some higher bit set
for, say, white, it would complicate my code quite a lot. Note trick Chess
Genius used (uses?): King and Rooks with castling rights have one of high bits
set to mark that... (I learned that from some source code to read CG/Mephisto
savegames); you may also try to make Q,R and B have same bit set (and reset for
other pieces) to indicate sliders...
If you already know/assume what operations on board you would do most - you
can try to construct most efficient representation for speed.
-Andrew-
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