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

[Ganesh Ajjanagadde]

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?
As per the documentation, it is C99 which is in general not safe to use.

I notice one use in entire codebase (line 515 of avformat/dump.c), so
it should be ok in my view.
I will resend the patch only after someone confirms the safety of
llabs on all platforms.

>
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