Is there any advantage to using pow(x,2) instead of x*x, with x double?

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.