Author: Gerd Isenberg
Date: 09:25:25 06/24/04
Go up one level in this thread
On June 23, 2004 at 18:30:57, Russell Reagan wrote:
>I am curious about a few design choices in Crafty. Some of the questions are
>general questions that anyone who is knowledgable could answer, so I ask this
>publicly instead of via email to Dr. Hyatt.
>
>First issue. Crafty is written with a lot of color-specific code, like:
>
>if (wtm) {
> // ...
>}
>else {
> // ...
>}
>
>This is what I think. The downside to this approach is that you double the size
>of the code, which is not cache friendly. This should be a bigger problem in a
>rotated bitboard engine where there are already cache issues.
I did that color-specific code too but maintainability is an issue here.
Meanwhile, for a lot of functions i use inlines with actual color parameter and
access (precalculated) data via color index.
doColorSpecificStuff(color2move);
One may easily duplicate code, e.g. by some conditional compiled macro this way
if ( color2move == white )
doColorSpecificStuff(white);
else
doColorSpecificStuff(black);
and to look from time to time what is actually faster.
If an actual parameter of an inlined function is a compile time constant,
compiler may be able to optimize the additional register usage away in that
special inlined incarnation of that function.
Another way to introduce compile time constants is to use integer templates with
C++ compiler supporting this correctly:
doColorSpecificStuff<int color2move> () {...}
and to call
if ( color2move == white )
doColorSpecificStuff<white>();
else
doColorSpecificStuff<black>();
>
>Another potential downside is that you introduce an extra branch. However, I
>think that this branch would be easily predictable, since the side to move will
>alternate back and forth, and so the branch decision will alternate.
I guess for leaf-nodes e.g. as childs of all nodes, those functions are often
called with same color in a row for N previous moves. Miss-predictions are
relative more expensive, if the bodies are really small.
Gerd
<snip>
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