Author: Russell Reagan
Date: 16:00:02 07/18/02
Go up one level in this thread
On July 18, 2002 at 13:23:23, Robert Hyatt wrote:
>I already do this. I have "Rank()" and "File()" macros that I use most
>everywhere already. Ditto for "From()", "To()", "Piece()", "Captured()" to
>extract that field from the 21 bit compressed move format I use internally.
I was actually wondering about something related to this just today. Perhaps you
could provide a little guidance on anything you see awkward or flat out wrong.
Would it be faster to do your approach and extract info from a packed 32-bit
unsigned int (or whatever size you'd like), or to do something like this...
union Piece {
struct {
unsigned char color;
unsigned char type;
unsigned char index;
unsigned char alive;
};
unsigned int piece;
};
Currently I do something like you do, and I have COLOR() and TYPE() macros that
extract the data from a 32-bit int. I have gone back and forth here. I have
thought about doing things in a manner similar to Gerbil, where your "board" is
an array of pointers into to piece array, but then in generating moves if you
have to test if there is a piece there, and if there is you have to do another
test for what kind of piece it is, and possibly it's color. Using my current
method, I can just say:
if(TYPE(squares[i]) == KNIGHT)
// then generate knight moves
The other approach would take more instructions:
if(squares[i] != NULL) // testing our array of piece pointers here
if(squares[i]->type == KNIGHT)
// generate knight moves
So one looks like you have the extra ANDing to do, and one you have the extra
testing and pointer dereferencing to do. These are things that bother me and I
don't know enough about ASM to answer them myself.
Using the union approach you could do access the fields that are on the 8-bit
boundaries, and if we needed to copy a piece (move it) we could just copy the
'piece' field of the Piece structure.
Would accessing those things be faster than using an ANDing approach? I'm not
very good with ASM, so I figure you can answer better than I can. Granted, if
you have more than 4 things you need to keep track of, you either have to use
the AND method that you use and pack more in, or you have to use another 32-bit
value to your structure. But for a structure with 4 or fewer things to keep
track of, would the union and anonymous struct method work faster than the
ANDing approach? In my mind I'm thinking that the ANDing approach needs that
extra AND, but maybe I'm missing something, since like I said, I'm not very keen
on the efficiency of various things when done in ASM.
These things make my head hurt. I can't decide whether it's better to get rid of
the ANDing and add a pointer dereference and extra testing or whether I should
use something like the union approach. I probably shouldn't be worrying about
things as trivial as this yet, but it still bothers me.
Russell
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