Why aren't cmath's pow and sqrt templates?

Question

As a matter of curiosity, why are std::sqrt and std::pow overloaded just for a single type of parameter? Why are they not implemented as function/functor templates?

Answer 1

They are overloaded for types float, double, and long double.

There are no other floating-point types, so there would be no advantage in a more general solution using templates.

The C++ <cmath> header is almost, but not quite, a copy of C's <math.h> header.

C doesn't have overloading, so it provides three different square root functions:

float sqrtf(float arg);
double sqrt(double arg);
long double sqrtl(long double arg);

and similarly for the other floating-point functions.

C++'s <cmath> provides those functions and overloaded versions of sqrt for all three floating-point types.

Here's an example that demonstrates this:

#include <iostream>
#include <iomanip>
#include <cmath>

int main() {
    auto f = std::sqrt(2.0F);
    auto d = std::sqrt(2.0);
    auto ld = std::sqrt(2.0L);
    std::cout << std::setprecision(64);
    std::cout << ' ' << sizeof f << ' '  << f  << '\n';
    std::cout << ' ' << sizeof d << ' '  << d  << '\n';
    std::cout        << sizeof ld << ' ' << ld << '\n';
}

The output on my system, demonstrating different size and precision for each call:

 4 1.41421353816986083984375
 8 1.4142135623730951454746218587388284504413604736328125
16 1.4142135623730950487637880730318329369765706360340118408203125