messing around with efficient multiplication algorithms for big integers modulo an integer N, using polynomial representations over the quotient ring Z/(qZ). in particular, with representative N->n(x) of degree d, considering the polynomial CRT interpretation of the DFT, in the rings Z_q[x]/(x^d+1),Z_q[x]/(x^d-1) and Z_q[x]/(x^(2d)-1)