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*         


        

Answer 1

In C++11 there is one case where there is an advantage to using x * x over std::pow(x,2) and that case is where you need to use it in a constexpr:

constexpr double  mySqr( double x )
{
      return x * x ;
}

As we can see std::pow is not marked constexpr and so it is unusable in a constexpr function.

Otherwise from a performance perspective putting the following code into godbolt shows these functions:

#include 

double  mySqr( double x )
{
      return x * x ;
}

double  mySqr2( double x )
{
      return std::pow( x, 2.0 );
}

generate identical assembly:

mySqr(double):
    mulsd   %xmm0, %xmm0    # x, D.4289
    ret
mySqr2(double):
    mulsd   %xmm0, %xmm0    # x, D.4292
    ret

and we should expect similar results from any modern compiler.

Worth noting that currently gcc considers pow a constexpr, also covered here but this is a non-conforming extension and should not be relied on and will probably change in later releases of gcc.