I feel like I must just be unable to find it. Is there any reason that the c++ pow function does not implement the "power" function for anything except floats and doubles?
I know the implementation is trivial, I just feel like I'm doing work that should be in a standard library. A robust power function (ie handles overflow in some consistent, explicit way) is not fun to write.
Because there's no way to represent all integer powers in an int anyways:
>>> print 2**-4
0.0625
pow(double, double), powl(long, long), and powf(float, float) are in math.h of the standard C libraries, and should therefore be available for use in C++.
Link to docs.
For any fixed-width integral type, nearly all of the possible input pairs overflow the type, anyway. What's the use of standardizing a function that doesn't give a useful result for vast majority of its possible inputs?
You pretty much need to have an big integer type in order to make the function useful, and most big integer libraries provide the function.
Uhm,
$ cat test.c
#include <stdio.h>
#include <math.h>
int main() {
printf("%f\n", pow(2, -4));
return 0;
}
$ gcc -lm test.c # -lm is used to include the math library
$ ./a.out
0.062500
Perhaps because the processor's ALU didn't implement such a function for integers, but there is such an FPU instruction (as Stephen points out, it's actually a pair). So it was actually faster to cast to double, call pow with doubles, then test for overflow and cast back, than to implement it using integer arithmetic.
(for one thing, logarithms reduce powers to multiplication, but logarithms of integers lose a lot of accuracy for most inputs)
Stephen is right that on modern processors this is no longer true, but the C standard when the math functions were selected (C++ just used the C functions) is now what, 20 years old?