are 2^n exponent calculations really less efficient than bit-shifts?

Question

if I do:

int x = 4;
pow(2, x);

Is that really that much less efficient than just doing:

1 << 4

?

Answer 1

That depends on the compiler, but in general (when the compiler is not totally braindead) yes, the shift is one CPU instruction, the other is a function call, that involves saving the current state an setting up a stack frame, that requires many instructions.