Pow() function and converting double to byte/int

@robtillaart
There are some things about the test that are not fair.
In the switch case, there is no use of the value that is computed in the switch case, so the whole switch statement gets optimized away. Uncommenting the int y = x; statement has no affect, since y is never used, so it, too, gets optimized away. Adding volatile in front of int on that statement, to prevent optimizing the whole block of code away results in the switch statement taking considerably longer.