[FFmpeg-devel] [PATCH] fifo: add av_fifo_grow()

[Michael Niedermayer]

On Mon, May 14, 2012 at 11:28:11PM +0200, Alexander Strasser wrote:
> Hi Michael,
> 
> Michael Niedermayer wrote:
> [...]
> > diff --git a/libavutil/fifo.c b/libavutil/fifo.c
> [...]
> > +int av_fifo_grow(AVFifoBuffer *f, unsigned int size)
> > +{
> > +    unsigned int old_size = f->end - f->buffer;
> > +    if(size + (unsigned)av_fifo_size(f) < size)
> > +        return AVERROR(EINVAL);
> > +
> > +    size += av_fifo_size(f);
> > +
> > +    if (old_size < size)
> > +        return av_fifo_realloc2(f, FFMAX(size, 2*size));
> > +    return 0;
> > +}
> 
>   I am no means an expert concerning the AVFifoBuffer implementation,
> but it looks like some of this is already done in av_fifo_realloc2
> and does not need to be duplicated in here.
> 
>   Where am I missing the point? :(

for(i=0; i<N; i++)
    av_fifo_realloc2(i) is slow

for(i=0; i<N; i++)
    av_fifo_grow(i) is fast 

why not fix av_fifo_realloc2()?
it could break some code using it that has specific expectations on
the resulting fifo size


    > 
> >  // src must NOT be const as it can be a context for func that may need updating (like a pointer or byte counter)
> >  int av_fifo_generic_write(AVFifoBuffer *f, void *src, int size, int (*func)(void*, void*, int))
> >  {
> > diff --git a/libavutil/fifo.h b/libavutil/fifo.h
> > index 22a9aa5..eabeec3 100644
> > --- a/libavutil/fifo.h
> > +++ b/libavutil/fifo.h
> > @@ -103,6 +103,18 @@ int av_fifo_generic_write(AVFifoBuffer *f, void *src, int size, int (*func)(void
> >  int av_fifo_realloc2(AVFifoBuffer *f, unsigned int size);
> >  
> >  /**
> > + * Enlarge an AVFifoBuffer.
> > + * In case of reallocation failure, the old FIFO is kept unchanged.
> > + * The new fifo size may be larger than the requested size.
> > + *
> > + * @param f AVFifoBuffer to resize
> > + * @param additional_space the additional space in addition to av_fifo_size()
> > + *        which the user wants.
> 
>   This could profit from a less awkward wording more in line with the
> other AVFifoBuffer docs. What do think of
> "the amount of space in bytes to allocate in addition to av_fifo_size()"
> ?

locally fixed

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

The worst form of inequality is to try to make unequal things equal.
-- Aristotle
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