Inverse Fast Fourier Transform : ifft

ifft takes as argument a list $\tt [b_0,..b_{N-1}]$ where N is a power of two.
ifft returns the list $\tt [a_0,..a_{N-1}]$ such that

$$\tt fft([a_0,..a_{N-1}])=[b_0,..b_{N-1}]$$

Input :

ifft([2,-1-i,0,-1+i])

Output :

[0.0, 1.0, 1.0, 0.0]