On Thu, Aug 08, 2019 at 11:59:12AM +0200, Nicolas George wrote:
> Michael Niedermayer (12019-08-08):
> > This provides an alternative to retry counters.
> > Useful if there is no reasonable maximum number of iterations and
> > no ordering that naturally avoids loops.
> >
> > Signed-off-by: Michael Niedermayer <mich...@niedermayer.cc>
> > ---
> > doc/APIchanges | 3 ++
> > libavutil/Makefile | 1 +
> > libavutil/loop_detector.h | 71 +++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 75 insertions(+)
> > create mode 100644 libavutil/loop_detector.h
> >
> > diff --git a/doc/APIchanges b/doc/APIchanges
> > index 6603a8229e..eee4c30ec5 100644
> > --- a/doc/APIchanges
> > +++ b/doc/APIchanges
> > @@ -15,6 +15,9 @@ libavutil: 2017-10-21
> >
> > API changes, most recent first:
> >
> > +2019-XX-XX - XXXXXXXXXX - lavu 56.XX.XXX - loop_detector.h
> > + Add loop_detector.h, av_is_loop(), AVSimpleLoopDetector
> > +
> > 2019-07-27 - xxxxxxxxxx - lavu 56.33.100 - tx.h
> > Add AV_TX_DOUBLE_FFT and AV_TX_DOUBLE_MDCT
> >
> > diff --git a/libavutil/Makefile b/libavutil/Makefile
> > index 57e6e3d7e8..0b77fa6347 100644
> > --- a/libavutil/Makefile
> > +++ b/libavutil/Makefile
> > @@ -48,6 +48,7 @@ HEADERS = adler32.h
> > \
> > intreadwrite.h \
> > lfg.h \
> > log.h \
> > + loop_detector.h \
> > macros.h \
> > mathematics.h \
> > mastering_display_metadata.h \
> > diff --git a/libavutil/loop_detector.h b/libavutil/loop_detector.h
> > new file mode 100644
> > index 0000000000..6f8643495a
> > --- /dev/null
> > +++ b/libavutil/loop_detector.h
> > @@ -0,0 +1,71 @@
> > +/*
> > + * Copyright (C) 2019 Michael Niedermayer (mich...@niedermayer.cc)
> > + *
> > + * This file is part of FFmpeg
> > + *
> > + * FFmpeg is free software; you can redistribute it and/or
> > + * modify it under the terms of the GNU Lesser General Public
> > + * License as published by the Free Software Foundation; either
> > + * version 2.1 of the License, or (at your option) any later version.
> > + *
> > + * FFmpeg is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> > + * Lesser General Public License for more details.
> > + *
> > + * You should have received a copy of the GNU Lesser General Public
> > + * License along with FFmpeg; if not, write to the Free Software
> > + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> > 02110-1301 USA
> > + */
> > +
> > +
> > +/**
> > + * @file
> > + * Utilties for detecting infinite loops
> > + * @author Michael Niedermayer <mich...@niedermayer.cc>
> > + */
> > +
> > +#ifndef AVUTIL_LOOP_DETECTOR_H
> > +#define AVUTIL_LOOP_DETECTOR_H
> > +
> > +typedef struct AVSimpleLoopDetector {
> > + uint64_t count;
> > + uint64_t state;
> > +} AVSimpleLoopDetector;
> > +
> > +/**
> > + * Checks if the list of states provided by the user fell into a cycle.
> > + *
>
> > + * To initialize or reset the detector, the context is simply memset to 0.
>
> I suggest:
>
> #define AV_SIMPLE_LOOP_DETECTOR_INIT {0}
>
> so we can extend it if needs be.will change it > > > + * This detector requires only 16bytes of context and minimal computations > > + * per iteration. In exchange for this simplicity it takes a few iterations > > + * into a loop before it is detected. > > + * No deallocation or memory allocation is needed. > > + * > > + * @param c The context, initialy and to reset, it is simply memset to > > 0. > > + * It is only 16bytes so as to be lightweight and not poison > > any > > + * data cache. > > + * > > > + * @param state The loop state, when this falls into a cycle the detector > > + * will after a few iterations return 1. > > + * > > + * @param max_iterations > > + * after this many iterations the detector will return 1 > > regardless > > + * of it falling into a cycle. > > Even with the code, I do not manage to understand exactly what it means, > in particular what the state is. The example uses a single state, so any > cycle is trivial. the idea is that until the state repeats the return will be 0 when there is a repeat the return may or may not switch to 1 when a final cycle is entered the return will reasonable quickly switch to 1 would this clarify it ? or should i explain this somehow differently or maybe the name for the variable isnt optimal ? in practive it most often will likely be a single variable like a byte offset in a file but i imagine it could be something more complex like a depth+offset or tagname+offset or something thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Everything should be made as simple as possible, but not simpler. -- Albert Einstein
signature.asc
Description: PGP signature
_______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
