On Tue, Nov 3, 2015 at 12:54 PM, Muhammad Faiz <mfc...@gmail.com> wrote: > On Tue, Nov 3, 2015 at 3:47 AM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote: >> On Tue, Nov 3, 2015 at 5:06 AM, Muhammad Faiz <mfc...@gmail.com> wrote: >>> On Sat, Oct 31, 2015 at 10:15 AM, Ganesh Ajjanagadde <gajja...@mit.edu> >>> wrote: >>>> On Fri, Oct 30, 2015 at 7:29 PM, Michael Niedermayer >>>> <mich...@niedermayer.cc> wrote: >>>>> On Fri, Oct 30, 2015 at 06:53:34PM -0400, Ganesh Ajjanagadde wrote: >>>>>> On Fri, Oct 30, 2015 at 6:35 PM, Michael Niedermayer <michae...@gmx.at> >>>>>> wrote: >>>>>> > From: Michael Niedermayer <mich...@niedermayer.cc> >>>>>> > >>>>>> > This should fix the build failure of avf_showcqt.c >>>>>> > >>>>>> > An alternative solution would be to add a check for fmin/fmax to >>>>>> > fate-source and >>>>>> > then to replace them by FFMIN/FFMAX, i can do that if preferred? >>>>>> > >>>>>> > Untested due to lack of a affected platform >>>>>> >>>>>> I recall some interest on my end to get fmin, fmax etc for different >>>>>> reasons, and it was remarked that commit >>>>>> 4436a8f44dedc83767b3d9da9beb85d1fae2ca30 may be relevant. The summary >>>>>> seems to be that getting it to work on all platforms is not so simple. >>>>> >>>>> :/ >>>>> ill replace the problematic ones by FFMIN/MAX for now so the build >>>>> failure on the affected msvc platforms is fixed >>>>> tieing a build fix to this complexity would be unwise >>>>> >>>>> >>>>>> I am definitely interested in getting it to work in order to replace >>>>>> FFMAX/FFMIN for floating point in especially libavfilter. This will >>>>>> allow better nan signalling at a slight performance cost. >>>>> >>>>> would that performance cost affect all systems or just ones not >>>>> having fmin/fmax ? >>>>> i think affecting all systems would be bad >>>> >>>> A correct fmin and fmax will be slower than FFMIN/FFMAX, simply >>>> because they do NaN handling. How much slower, I have not tested. Also >>>> note that flags may be passed to the compiler to ignore NaN's, >>>> something which can possibly be done locally if desired. However, I >>>> view FFMAX/FFMIN as the cleaner solution if NaN signalling/propagation >>>> is not an issue, so I may not pursue this. >>>> >>> >>> Common problem with FFMIN/FFMAX (and other macros that evaluates >>> arguments more than once): >>> FFMAX(a, myfunc(b)) >>> will call myfunc twice (OK compiler may optimize it and call myfunc once) >>> and often people don't care about it. >> >> That goes without saying, but sometimes compiler can't optimize due to >> sequence point stuff. This is why the macro should be used cautiously. >> However, FFmpeg devs are generally cautious about these things so I no >> longer press this that hard. The real technical benefit (if any) is >> the different NaN handling as noted above. > > Here some examples: > libavfilter/g729postfilter.c: 544 > *voicing = FFMAX(*voicing, long_term_filter(adsp, pitch_delay_int, > residual, > residual_filt_buf + 10, > subframe_size)); > > others that call sqrt, strlen, etc (altough possibly compiler can optimize it) > > commit 94494dab910133106e80ece0f79935d78138e415 > + volume = FFABS(av_expr_eval(volume_expr, expr_vars_val, NULL)); > I posted the patch, and I didn't noticed or warned that it is wrong.
So on the note of FFABS - I think all floating point usages at least have been converted to proper C functions. Yes, things like this can be missed, and I personally use the libc variants unless there is no alternative. However, it was quite some work for me to convince others to use them, and I am trying to stay on the sidelines this time by not posting a patch for it. > > Thank's > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
