I have just subscribed to this mailing-list even if I am very interested in both programming and primes search. I intend to write a program to find prime Mersenne numbers using Lucas-Lehmer test and FFT in Z/mZ (the ring of integers modulo an prime integer m). The language I use for this purpose is Caml-Light, but I also know C and Pascal languages. I represent big numbers with arrays. I choose m=7*2^26+1. Thus, I have 26 free bits per element of arrays, so I decide to represent my big numbers in binary using the 26 first bits of each elements of arrays. I have a problem with the multiplication (the square). When I do the IFFT, to get back 'the coefficients of the polynom' that represents the number I have to square, I may get a 'coefficient' between 2^26 and 7*2^26+1 since all operations are modulo m. What do I have to do with the 26th,27th and 28th bits ? P.S.:I have already read the FAQ ; I just want to make a FFT to multiply numbers without taking the result mod a Mersenne number.
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