FFT Multiplication on Disk?

Hi.

I was playing around with a new hard drive-based Fast Fourier
Transform multiplication program. What it's supposed to do is take two
numbers stored on disk and then multiply them using only one full-
sized FFT, and it _does the FFT on disk_, since it is too large to
fit in RAM. (instead of using a Karatsuba divide-and-conquer approach
like I did with the pi program I've been discussing here.) I thought
it would be a good idea to use Bailey's "6-step" method, as that
requires 2 sqrt(N) transforms of sqrt(N) length, which easily fit in
RAM for the sizes of N I'm considering (hence one could actually do
several of them in RAM. (On a multicore processor one could easily
parallelize those, by the way.)) can actually do. However the problem
is that this involves three in-place matrix transpositions of a square
matrix. Does anyone know of an efficient algorithm to do those? That's
my big chokepoint insofar as the Matrix-based 6-Step Fft goes.

.

Relevant Pages

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