Author: Matt Taylor
Date: 10:25:30 01/01/03
Go up one level in this thread
On January 01, 2003 at 11:50:58, Lieven Clarisse wrote:
>I was wondering if there is a good book about how to write efficient C code. I
>am not talking about algorithms, but the way *how* to write things, eg
>
>which is faster :
>do {} while() or while () {}
>
>-------
>I know for instance that:
>
>ptr=&R[i];
>if((*ptr==3)||(*ptr==7)) {;}
>
>is faster then:
>
>if((R[i]==3)||(R[i]==7)) {;}
>
>Is there a good book that reviews all those kinds of tricks?
>
>regards,
>
>Lieven
It varies per compiler. There is an even faster method for your second case:
x = R[i];
if (x == 3 || x == 7) {;}
The only way to know is to look at compiler output. I know for VC, the compiler
I use most often, it chokes on 64-bit manipulations, stack alignment > 4 bytes,
and small structures. It usually generates nice code with conditionals such as:
int is_below(int x, int y)
{
return (x < y ? 1 : 0);
}
-Matt
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