Re: why use pow(x, 2)?
Re: why use pow(x, 2)?
- Subject: Re: why use pow(x, 2)?
- From: Chris Williams <email@hidden>
- Date: Mon, 02 Nov 2009 14:01:14 -0800
- Thread-topic: why use pow(x, 2)?
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@hidden>
> 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 íi, %xmm0 // convert int argc to float
> mulsd %xmm0, %xmm0 // pow(argc, 2)
> cvttsd2si %xmm0, êx // convert float->int for return
> leave
> ret
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