[FFmpeg-devel] [PATCH] Add and use av_fast_padded_malloc.

Michael Niedermayer michaelni at gmx.at
Tue Jan 17 18:17:44 CET 2012


On Tue, Jan 17, 2012 at 08:08:48AM +0100, Reimar Döffinger wrote:
> On Tue, Jan 17, 2012 at 04:26:43AM +0100, Michael Niedermayer wrote:
> > On Tue, Jan 17, 2012 at 12:18:17AM +0100, Reimar Döffinger wrote:
> > > The same as av_fast_malloc but uses av_mallocz and keeps extra
> > > always-0 padding.
> > > This does not mean the memory will be 0-initialized after each call,
> > > but actually only after each growth of the buffer.
> > > However this makes sure that
> > > a) all data anywhere in the buffer is always initialized
> > > b) the padding is always 0
> > > c) the user does not have to bother with adding the padding themselves
> > > Fixes another valgrind warning about use of uninitialized data,
> > > this time with fate-vsynth1-jpegls.
> > > 
> > > Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
> > 
> > LGTM
> 
> I wonder if it would be better to make the size of the padding an
> argument.
> Because I also needed below patch.
> Though not having to specify the padding size in almost all cases
> might be worth having to memset manually in a rare few.
> Note that I think the "si" code that tries to detect if a memset
> is necessary is completely broken and I have some doubts trying
> to avoid it will give any relevant speedup (how often will the
> size be exactly the same?)

it should be exactly the same unless the buffer size is increased
which should be only O(log n) times

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

He who knows, does not speak. He who speaks, does not know. -- Lao Tsu
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