Arithmetic modulo 2^n+1. A fermat of length w+1 represents a number modulo 2^(w*_W) + 1. The last word is zero or one. A number has at most two repres

A polValues represents the value of a poly at the powers of a K-th root of unity θ=2^(l/2) in Z/(b^n+1)Z, where b^n = 2^(K/4*l).

poly represents an integer via a polynomial in Z[x]/(x^K+1) where K is the FFT length and b^m is the computation basis 1<<(m*_W). If P = a[0] + a[1] x