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

[Aurelien Jacobs]

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.

Aurel
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