[FFmpeg-devel] Re: [PR] avutil/mem: Add av_malloc_with_paddingz() (PR #21509)

[Michael Niedermayer via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

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On Mon, Jan 19, 2026 at 08:44:23AM +0000, Kieran Kunhya via ffmpeg-devel wrote:
> On Mon, 19 Jan 2026, 04:22 michaelni via ffmpeg-devel, <
> ffmpeg-devel@ffmpeg.org> wrote:
> 
> > PR #21509 opened by michaelni
> > URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21509
> > Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21509.patch
> >
> > Add a av_malloc() that adds padding like AV_INPUT_BUFFER_PADDING_SIZE
> > and clears it.
> >
> > This is a operation we commonly use so this function should simplify
> > many cases
> >
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> >
> >
> > >From cc424b2a5568ee35a3435ff58a84d2a18c1c6843 Mon Sep 17 00:00:00 2001
> > From: Michael Niedermayer <michael@niedermayer.cc>
> > Date: Mon, 19 Jan 2026 05:15:23 +0100
> > Subject: [PATCH] avutil/mem: Add av_malloc_with_paddingz()
> >
> > Add a av_malloc() that adds padding like AV_INPUT_BUFFER_PADDING_SIZE
> > and clears it.
> >
> > This is a operation we commonly use so this function should simplify
> > many cases
> >
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavutil/mem.c | 10 ++++++++++
> >  libavutil/mem.h | 13 +++++++++++++
> >  2 files changed, 23 insertions(+)
> >
> > diff --git a/libavutil/mem.c b/libavutil/mem.c
> > index b205d3fb25..aac7ef4d12 100644
> > --- a/libavutil/mem.c
> > +++ b/libavutil/mem.c
> > @@ -261,6 +261,16 @@ void *av_mallocz(size_t size)
> >      return ptr;
> >  }
> >
> > +void *av_malloc_with_paddingz(size_t size, size_t padding)
> > +{
> > +    if (size > SIZE_MAX - padding)
> > +        return NULL;
> > +    uint8_t *p = av_malloc(size + padding);
> > +    if(p)
> > +        memset(p + size, 0, padding);
> > +    return p;
> > +}
> > +
> >  void *av_calloc(size_t nmemb, size_t size)
> >  {
> >      size_t result;
> > diff --git a/libavutil/mem.h b/libavutil/mem.h
> > index ab7648ac57..6a4c144f18 100644
> > --- a/libavutil/mem.h
> > +++ b/libavutil/mem.h
> > @@ -129,6 +129,19 @@ void *av_malloc(size_t size) av_malloc_attrib
> > av_alloc_size(1);
> >   */
> >  void *av_mallocz(size_t size) av_malloc_attrib av_alloc_size(1);
> >
> > +/**
> > + * Allocate a memory block with alignment suitable for all memory accesses
> > + * (including vectors if available on the CPU)
> > + *
> > + * An additional padding will be allocated and cleared.
> > + *
> > + * @param size Size in bytes for the memory block to be allocated
> > + * @param padding Size in bytes of padding allocated and zeroed after
> > size.
> > + * @return Pointer to the allocated block, or `NULL` if it cannot be
> > allocated
> > + * @see av_malloc()
> > + */
> > +void *av_malloc_with_paddingz(size_t size, size_t padding)
> > av_malloc_attrib av_alloc_size(1);
> > +
> >  /**
> >   * Allocate a memory block for an array with av_malloc().
> >   *
> > --
> > 2.52.0
> >
> > _______________________________________________
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> > To unsubscribe send an email to ffmpeg-devel-leave@ffmpeg.org
> 
> 
> Seems a bit wordy. av_malloc_paddedz instead?

yes, i changed it to james suggestions of av_padded_malloc(),

[...]

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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact

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