Why is pow(int, int) so slow?

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pow() works with real floating-point numbers and uses under the hood the formula

pow(x,y) = e^(y log(x))

to calculate x^y. The int are converted to double before calling pow. (log is the natural logarithm, e-based)

x^2 using pow() is therefore slower than x*x.

Edit based on relevant comments

  • Using pow even with integer exponents may yield incorrect results (PaulMcKenzie)
  • In addition to using a math function with double type, pow is a function call (while x*x isn’t) (jtbandes)
  • Many modern compilers will in fact optimize out pow with constant integer arguments, but this should not be relied upon.

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