Mail Archives: djgpp/1998/07/27/13:40:18
EDWARD CASHIN <cashin AT pollux DOT cs DOT uga DOT edu> wrote:
> Hello. I was just considering the case of a circular
> buffer. Indexing the subscripts could be done with
> something like this:
>
> /* subscripts: "front" is subscript of first stored value
> "back" is subscript of last stored value
> "last" is subscript of the last available
> array spot */
>
> front = (front + 1 > last) ? 0 : front + 1;
> back = (back + 1 > last) ? 0 : back + 1;
>
> ...or you could say:
>
> front = (++front) % last;
> back = (++back) % last;
>
> ...which begs the question, "How fast is the modulo?"
> and more specifically, how is it implemented?
Modulo is just the rest of a division. So if last is a variable (not a macro
and not a constant) you'll get a div or idiv and that's sllloooowwww.
But I think you must call gcc with -S to take a look at the generated
assembler ;-)
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