[FFmpeg-cvslog] r14956 - trunk/libavformat/matroskadec.c

[Michael Niedermayer]

On Tue, Aug 26, 2008 at 04:56:15AM +0200, Aurelien Jacobs wrote:
> Robert Swain wrote:
> 
> > 2008/8/26 Aurelien Jacobs <aurel at gnuage.org>:
> > > Robert Swain wrote:
> > >
> > >> 2008/8/26 Mike Melanson <mike at multimedia.cx>:
> > >> > Michael Niedermayer wrote:
> > >> >> On Mon, Aug 25, 2008 at 11:51:52PM +0200, Aurelien Jacobs wrote:
> > >> >>> Mike Melanson wrote:
> > >> >>>
> > >> >>>> aurel wrote:
> > >> >>>>> Author: aurel
> > >> >>>>> Date: Mon Aug 25 01:57:29 2008
> > >> >>>>> New Revision: 14956
> > >> >>>>>
> > >> >>>>> Log:
> > >> >>>>> matroskadec: don't try to seek to negative timestamp
> > >> >>>>> matroska timestamps are unsigned
> > >> >>>>>
> > >> >>>>>
> > >> >>>>> Modified:
> > >> >>>>>    trunk/libavformat/matroskadec.c
> > >> >>>> Either 14955 or 14956 (both from you) broke the seek regressions.
> > >> >>>> Representative breakage:
> > >> >>> Grmlll... I was pretty sure those commit would change the seek
> > >> >>> regressions. But when I wanted to test this, I just couldn't
> > >> >>> run the test due to the wma regression (floating-point issue IIRC,
> > >> >>> running on amd64).
> > >> >>
> > >> >> Which commit did cause this wma regression test failure?
> > >
> > > I thought it was due to r14698 as this was already discussed, and I
> > > got the same md5. But In fact it's not.
> > >
> > >> > One of the 3 revisions following 14755 broke WMA. According to an
> > >> > earlier email, it was 14758, specifically.
> > >
> > > Almost. It's in fact r14757 which broke reg tests for me.
> > 
> > Before r14757:
> > 
> > /* init MDCT windows : simple sinus window */
> > for(i = 0; i < s->nb_block_sizes; i++) {
> >     int n, j;
> >     float alpha;
> >     n = 1 << (s->frame_len_bits - i);
> >     window = av_malloc(sizeof(float) * n);
> >     alpha = M_PI / (2.0 * n);
> >     for(j=0;j<n;j++) {
> >         window[j] = sin((j + 0.5) * alpha);
> >     }
> >     s->windows[i] = window;
> > }
> > 
> > Now:
> > 
> > // Generate a sine window.
> > void ff_sine_window_init(float *window, int n) {
> >     int i;
> >     for(i = 0; i < n; i++)
> >         window[i] = sin((i + 0.5) / (2 * n) * M_PI);
> > }
> > 
> > and
> > 
> > /* init MDCT windows : simple sinus window */
> > for(i = 0; i < s->nb_block_sizes; i++) {
> >     int n;
> >     n = 1 << (s->frame_len_bits - i);
> >     ff_sine_window_init(ff_sine_windows[s->frame_len_bits - i - 7], n);
> >     s->windows[i] = ff_sine_windows[s->frame_len_bits - i - 7];
> > }
> > 
> > Why does this work fine with some compilers and not with others? Why
> > does it not work fine on some archs and not others with the same
> > compiler?
> 
> Difference seems to be "* alpha" vs. "/ (2 * n) * M_PI".
> Probably a float precision/rounding issue...
> Attached patch fixes reg tests on amd64.

patch ok

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The misfortune of the wise is better than the prosperity of the fool.
-- Epicurus
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