On Tue, Jun 13, 2017 at 12:10:07AM -0400, Kevin Mark wrote: > On Mon, Jun 12, 2017 at 9:42 PM, Michael Niedermayer > <mich...@niedermayer.cc> wrote: > > why is there a cast at all ? > > The cast is there because if you run this: > > ffmpeg -frames:v 5 -filter_complex > "sws_flags=+accurate_rnd+bitexact;testsrc=size=320x240 > [main];testsrc=size=640x360 [ref];[main][ref] > scale2ref=0:print(ow/641) [main][ref];[ref] nullsink" -map "[main]" > -flags +bitexact -fflags +bitexact -f md5 - > > This works just fine without a cast for ow. 0 == 0 is true so we set > it to 640. But for oh, the print() shows that ow/641 is 0.998440. When > it is truncated from a double to an integer (eval_h = res) it becomes > 0. But in our comparison, 0.998440 == 0 is false so in this case > eval_h will be truncated to 0 which is exactly the behavior we're > trying to correct. Adding that cast resolves the issue. 0.998440 == 0 > is false but (int) 0.998440 == 0 is true. > > For the extra cast I was talking about consider this: > > ffmpeg -frames:v 5 -filter_complex > "sws_flags=+accurate_rnd+bitexact;testsrc=size=320x240 > [main];testsrc=size=640x360 [ref];[main][ref] > scale2ref=500/6:print(print(ow)*5) [main][ref];[ref] nullsink" -map > "[main]" -flags +bitexact -fflags +bitexact -f md5 - > > That will print() 83.333333 and then 416.666667. A user might > (reasonably, in my opinion) expect that the ow value (or oh) is always > an integer. With the extra cast you'll see 83.000000 and 415.000000 > printed. 83.333333 truncates to 83 so no (noticeable) change for ow > but 416.666667 does not truncate to 415 so this is an example of a > place where the lack of truncation for ow/oh does change the outcome.
ok, makes sense i agree the 2nd cast seems a good idea > > I hope this clears it up. Perhaps that code should just be entirely > refactored to be a little more clear? > > Thanks, > Kevin > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB You can kill me, but you cannot change the truth.
signature.asc
Description: Digital signature
_______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
