R: fastest way to calculate sum over vector? [closed]

Let k and j be vectors.

I need to calculate the value sum(f(j) g(k[i])) for every i = 1, ..., length(k) for two functions g and f (that are vectorized).

So, in other words, the sum is over each element in j and I need to calculate that sum for every element in k, so that I end up with length(k) different sums.

What is the fastest way to do this in R?