[FFmpeg-devel] [PATCH][RFC] swresample/dither: use integer arithmetic

[Michael Niedermayer]

On Sun, Aug 23, 2015 at 03:10:40PM -0400, Ganesh Ajjanagadde wrote:
> On Sun, Aug 23, 2015 at 2:45 PM, Michael Niedermayer
> <michael at niedermayer.cc> wrote:
> > On Sun, Aug 23, 2015 at 02:28:07PM -0400, Ganesh Ajjanagadde wrote:
> >> This fixes a -Wabsolute-value reported by clang 3.5+ complaining about misuse of fabs() for integer absolute value.
> >> An additional benefit is the removal of floating point calculations.
> >> Note that the behaviors are not exactly identical, but should be ok in most situations.
> >>
> >> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> >> ---
> >>  libswresample/dither.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/libswresample/dither.c b/libswresample/dither.c
> >> index 248062a..fc08932 100644
> >> --- a/libswresample/dither.c
> >> +++ b/libswresample/dither.c
> >> @@ -109,7 +109,7 @@ av_cold int swri_dither_init(SwrContext *s, enum AVSampleFormat out_fmt, enum AV
> >>      memset(s->dither.ns_errors, 0, sizeof(s->dither.ns_errors));
> >>      for (i=0; filters[i].coefs; i++) {
> >>          const filter_t *f = &filters[i];
> >> -        if (fabs(s->out_sample_rate - f->rate) / f->rate <= .05 && f->name == s->dither.method) {
> >> +        if ((abs(s->out_sample_rate - f->rate) <= f->rate / 20) && f->name == s->dither.method) {
> >
> > unneeded () and the identical  condition should be used if possible
> 
> Thanks for pointing this out, will change.
> 
> >
> > something like
> > llabs(s->out_sample_rate - f->rate) * 20 <= f->rate
> 
> I initially thought of this approach, but went with my current patch
> because I was afraid of overflow with abs().
> llabs() is a good clean solution, but is it available on all platforms?

you can use FFABS() with 64bit arguments

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Let us carefully observe those good qualities wherein our enemies excel us
and endeavor to excel them, by avoiding what is faulty, and imitating what
is excellent in them. -- Plutarch
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