Question

is there any advantage to using this code

double x;
double square = pow(x,2);

instead of this?

double x;
double square = x*x;

I prefer x*x and looking at my implementation (Microsoft) I find no advantages in pow because x*x is simpler than pow for the particular square case.

Is there any particular case where pow is superior?

Answer 1

FWIW, with gcc-4.2 on MacOS X 10.6 and -O3 compiler flags,

x = x * x;

and

y = pow(y, 2);

result in the same assembly code:

#include <cmath>

void test(double& x, double& y) {
        x = x * x;
        y = pow(y, 2);
}

Assembles to:

    pushq   %rbp
    movq    %rsp, %rbp
    movsd   (%rdi), %xmm0
    mulsd   %xmm0, %xmm0
    movsd   %xmm0, (%rdi)
    movsd   (%rsi), %xmm0
    mulsd   %xmm0, %xmm0
    movsd   %xmm0, (%rsi)
    leave
    ret

So as long as you’re using a decent compiler, write whichever makes more sense to your application, but consider that pow(x, 2) can never be more optimal than the plain multiplication.