As we know :
FFT inverse ( FFT(A) wise element* FFT(B) )
may same as
convolve A and B
However:
I do this on python
import scipy
c = scipy.fft.fft([3,4,1,2])
d = scipy.fft.fft([2,5,4,9])
print(scipy.fft.ifft((c*d)))
[56.+0.j 40.+0.j 52.+0.j 52.-0.j]
print(np.convolve([3,4,1,2],[2,5,4,9]))
[ 6 23 34 52 50 17 18]
Why some of the index elements added?