On 4 January 2017 at 22:45, Rostislav Pehlivanov <[email protected]> wrote:
> > > On 4 January 2017 at 14:14, Peter Barfuss <[email protected]> wrote: > >> First off, many thanks. >> >> > + const int inv_1 = l_ptwo << ((4 - b_ptwo) & 3); >> > + const int inv_2 = 0xeeeeeeef & ((1U << b_ptwo) - 1); >> >> It would be nice to add a comment here that the expression for inv_1 >> is (2^b_ptwo)^-1 mod 15 and inv_2 is 15^-1 mod 2^b_ptwo. (A general >> PFA FFT would need to use extended Euclidean algorithm here, but >> because both cases are fixed, it simplifies to these expressions. I >> have a sketch of a proof (basically solving the relevant diophantine >> equation you get) in case anyone is nervous, though it's easy to >> verify by hand for 1 < b_ptwo < 18, which are all the cases that >> ffmpeg's power-of-two FFT currently supports). >> >> Rest of patch seems good. >> >> -Peter >> _______________________________________________ >> ffmpeg-devel mailing list >> [email protected] >> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel >> > > Done > > Also I didn't like how s->exptab[20].re needed a negative sign so I > removed it > and moved the subtraction to the 5-point FFT, just so you know. > > > I'll push both patches tomorrow evening if no one else has anything to say. > Applied, Thanks _______________________________________________ ffmpeg-devel mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
