According to the spec:
The two-argument form pow(x, y) is equivalent to using the power
operator: x**y.
The arguments must have numeric types. With mixed operand types, the
coercion rules for binary arithmetic operators apply.
In other words: since x is a float, the exponent is converted from an int to a float, and the generic floating-point power operation is performed. Internally, this is usually rewritten as:
x**y = 2**(y*lg(x))
2**a and lg a (base 2 logarithm of a) are single instructions on modern processors, but it is still takes much longer than a couple of multiplications.
