MacArthur, Ian (SELEX) (UK) wrote:
> I've looked at the code generated for integer mod operations
> in the past, and a lot of compilers make a real mess of it..
Really? Noticeably?
I believe you, as sometimes compilers can sometimes make ugly assembly,
but I figure that's an exception to the rule. And surely they won't
get it wrong.
Usually % just maps to an "IDIV", IIRC from my 8086 days.
Even today, it doesn't look too bad:
% cat foo.C
#include <time.h>
int main() {
int x = time(NULL);
x = x % 20; // <--
return(x);
}
% g++ -g -c -Wa,-adhln -O1 foo.C | more
[..]
4:foo.C **** x = x % 20; // <--
31 .loc 1 4 0
32 0013 BA14000000 movl $20, %edx
33 0018 89D1 movl %edx, %ecx
34 001a 99 cltd
35 001b F7F9 idivl %ecx
[..]
Removing -O1 is pretty much the same result.
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