PR#11477

So maybe convolve(x,y) should take care if  x or y is of prime size ?

Or users could at least be warned that this implementation of "Fast
Convolution" is not able to handle x
of prime size in acceptable time.

Anyway, I don't understand why R does not make use of a fast&free
algorithm like the FFTW implementation,
which is able to handle  x  of prime sizes in acceptable time.
"Sizes with small prime factors are best, but FFTW uses O(N log N)
algorithms even for prime sizes."

Ralf.