I can't speak for others, but I never meant to actually argue that pow
(x, 2) is clearer than x * x. My argument was that each author should
use whichever version he or she thinks is clearer. There are rarely
absolutes about that sort of thing, as clarity is subjective by its
very nature. I urge programmers to use the clearer choice, whatever
that might be to them.
Luke
On Nov 2, 2009, at 2:01 PM, Chris Williams wrote:
How completely rude of you, Greg, to confuse a good argument with
facts :)
But it still does leave the style question: is pow(x,2) clearer than
x*x?
In the case from the OP, I think that the pow is clearer, because it
is
implementing an algorithm that calls specifically for x-squared.
And in the
case where x is not a simple variable, but rather an expression,
it's even
more clear (and less prone to typing errors).
My $0.02...
From: Greg Parker <[email protected]>
Subject: Re: why use pow(x, 2)?
This is easy to test empirically. In this simple case, the compiler
does optimize pow(x, 2) directly to a single-instruction x*x.
% cat test.c
#include <math.h>
int main(int argc, char **argv) {
return pow(argc, 2);
}
% cc -O3 test.c -o - -S
[...]
_main:
LFB17:
pushq %rbp // build stack frame
LCFI0:
movq %rsp, %rbp // build stack frame
LCFI1:
cvtsi2sd %edi, %xmm0 // convert int argc to float
mulsd %xmm0, %xmm0 // pow(argc, 2)
cvttsd2si %xmm0, %eax // convert float->int for return
leave
ret
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