Pow() vs. exp() performance

Question

I was wondering if exp() is faster than more general pow(). I run fast benchmark on JsPerf http://jsperf.com/pow-vs-exp and it shown interesting result

Answer 1

Regardless of the architecture details, Math.pow has to do more in terms of error checking (for example, what happens if the base is negative?). than Math.exp (and as such I'd expect pow to be slower).

Relevant parts of the spec:

http://ecma-international.org/ecma-262/5.1/#sec-15.8.2.8

15.8.2.8 exp (x)

Returns an implementation-dependent approximation to the exponential function of x (e raised to the power of x, where e is the base of the natural logarithms).

If x is NaN, the result is NaN. If x is +0, the result is 1. If x is −0, the result is 1. If x is +∞, the result is +∞. If x is −∞, the result is +0.

http://ecma-international.org/ecma-262/5.1/#sec-15.8.2.13

15.8.2.13 pow (x, y)

Returns an implementation-dependent approximation to the result of raising x to the power y.

If y is NaN, the result is NaN. If y is +0, the result is 1, even if x is NaN. If y is −0, the result is 1, even if x is NaN. If x is NaN and y is nonzero, the result is NaN. If abs(x)>1 and y is +∞, the result is +∞. If abs(x)>1 and y is −∞, the result is +0. If abs(x)==1 and y is +∞, the result is NaN. If abs(x)==1 and y is −∞, the result is NaN. If abs(x)<1 and y is +∞, the result is +0. If abs(x)<1 and y is −∞, the result is +∞. If x is +∞ and y>0, the result is +∞. If x is +∞ and y<0, the result is +0. If x is −∞ and y>0 and y is an odd integer, the result is −∞. If x is −∞ and y>0 and y is not an odd integer, the result is +∞. If x is −∞ and y<0 and y is an odd integer, the result is −0. If x is −∞ and y<0 and y is not an odd integer, the result is +0. If x is +0 and y>0, the result is +0. If x is +0 and y<0, the result is +∞. If x is −0 and y>0 and y is an odd integer, the result is −0. If x is −0 and y>0 and y is not an odd integer, the result is +0. If x is −0 and y<0 and y is an odd integer, the result is −∞. If x is −0 and y<0 and y is not an odd integer, the result is +∞. If x<0 and x is finite and y is finite and y is not an integer, the result is NaN.