Author: Ulrich Tuerke
Date: 03:36:59 12/05/01
Go up one level in this thread
On December 05, 2001 at 05:33:08, Uri Blass wrote:
>In my program I have the following commands when I generate my pin arrays:
>
>if (color(sq)==side)
>{
> pin[sq]=-1;
> d=direction[kingsquare[color(sq)]][sq];
>...
>
>The strange speed demage to my program happens when I try to replace color(sq)
>with side in the last line
>
>color(sq) is more complicated to find then finding side that is simply integer.
>I expected that in the worst case there will be no speed change thanks to
>optimazion of compiler but I did not imagine that my program could run slower
>when I do something simpler.
>
>some data about my program that may help:
>
>
>
>my defs.h file includes
>
>#define color(target) (((info[target])>>3)&3)
>
>
>my data.c file includes
>
>int info[64];
>int side;
>int direction[64][64];
>int kingsquare[2];
>int pin[64];
>
>you can see that calculating color(sq) is not something simple(you need first to
>calculate info[sq] and later to calculate from it the value for color(sq))
>
>Uri
Perhaps the data types could be a reason for some microscopic effects. If the
variable "side" is for instance of type "short", the compiler has to zero-extend
the variable to word-size before indexing (because of the array access).
OTOH, the result of the expression is perhaps still stored in a hardware
register, and so has the right size to be used for indexing immediately.
Just a guess. I think that your observation may be also depend on implementation
details of the compiler in use. Another compiler might behave different.
Uli
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