[FFmpeg-devel] [PATCH] Doxygenate libavutil/mem.h

[Stefano Sabatini]

On date Tuesday 2007-09-25 21:53:57 +0200, Stefano Sabatini encoded:
> On date Sunday 2007-09-23 22:11:37 -0400, Rich Felker encoded:
> > On Sun, Sep 23, 2007 at 09:47:44PM +0200, Michael Niedermayer wrote:
> > > Hi
> > > 
> > > On Sat, Sep 22, 2007 at 03:18:16PM +0200, Stefano Sabatini wrote:
> [...]
> > > > I amended the previous patch eliminating in the av_realloc
> > > > documentation all the references to other functions implementations,
> > > > hope it is now more correct.
> > > > 
> [...]
> > > > Index: libavutil/mem.h
> > > > ===================================================================
> > > > --- libavutil/mem.h	(revision 10549)
> > > > +++ libavutil/mem.h	(working copy)
> > > > @@ -33,26 +33,47 @@
> > > >  #endif
> > > >  
> > > >  /**
> > > > - * Memory allocation of size byte with alignment suitable for all
> > > > + * Allocates a block of \p size bytes with alignment suitable for all
> > > >   * memory accesses (including vectors if available on the
> > > 
> > > > - * CPU). av_malloc(0) must return a non NULL pointer.
> > > > + * CPU). av_malloc(0) must return a non-NULL pointer.
> > > 
> > > i know this isnt new but its not true, av_malloc(0) will return NULL if
> > > malloc(0) does in some cases
> > 
> > As rightly it should. Implementations which return non-NULL for
> > zero-size mallocs are fundamentally stupid despite being valid.
> > 
> > > i dont know if its better to change the implementation or the docs but either
> > > one must be changed ...
> > 
> > Change the docs. There's no reason to force libavutil to mimic stupid
> > glibc behavior. Either it should force the sane behavior or leave it
> > unspecified...
> 
> I left it unspecified, but at the same time I'm also stating:
> @note av_malloc(0) return value is actually undefined, but future
> versions might force it to be a non-NULL value.
> 
> Is this solution acceptable?
> 
> (Same note added to av_mallocz docs too.)
> 
> > > > - * av_realloc semantics (same as glibc): if ptr is NULL and size > 0,
> > > > - * identical to malloc(size). If size is zero, it is identical to
> > > > - * free(ptr) and NULL is returned.
> > > > + * Allocates or reallocates a block of size \p size with alignment
> > > > + * suitable for all memory accesses (including vectors if available on
> > > > + * the CPU).
> > > 
> > > this is not true, the alignment will be as bad as what realloc() returns
> > > currently, we could fix the implementaton (IIRC there where some patches)
> > > but it would slow down av_realloc() considerably (>2x) if the realloc()
> > > output isnt aligned
> 
> This time I learnt that I have to actually *read* the implementation
> rather than just guess... 

[...]

Ping.

Regards.
-- 
Stefano Sabatini
Linux user number 337176 (see http://counter.li.org)
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