[Ffmpeg-devel] [RFC] another attempt at memalign realloc

[Michael Niedermayer]

Hi

On Wed, Dec 06, 2006 at 05:34:12PM +0100, Reimar D?ffinger wrote:
> Hello,
> I came up with the attached idea, but it seems so simple that I can't
> get rid of the feeling there is yet another problem with that (except
> that the performance might be really bad), otherwise somebody should
> have had that same idea during all this wild hacking around on it *g*.
> Well, please help me and have a very close look at it and say what you
> think.
> 
> Greetings,
> Reimar D?ffinger

> Index: libavutil/mem.c
> ===================================================================
> --- libavutil/mem.c	(revision 7217)
> +++ libavutil/mem.c	(working copy)
> @@ -105,6 +105,7 @@
>  {
>  #ifdef CONFIG_MEMALIGN_HACK
>      int diff;
> +    void *ptr2;
>  #endif
>  
>      /* let's disallow possible ambiguous cases */
> @@ -112,10 +113,17 @@
>          return NULL;
>  
>  #ifdef CONFIG_MEMALIGN_HACK
> -    //FIXME this isn't aligned correctly, though it probably isn't needed
>      if(!ptr) return av_malloc(size);
>      diff= ((char*)ptr)[-1];
> -    return realloc(ptr - diff, size + diff) + diff;
> +    ptr2 = realloc(ptr - diff, size + 16) + diff;
> +    if(!((int)ptr2&15))

hmm didnt this cast cause same silly warning with gcc on x86-64 or
something, anyway long and int casts are mixed not a real issue though


> +        return ptr2;
> +    ptr = ptr2 - diff;

void * arithmetic


> +    diff= ((-(long)ptr - 1)&15) + 1;
> +    ptr += diff;
> +    memove(ptr, ptr2, size);
> +    ((char*)ptr)[-1]= diff;
> +    return ptr;


the comment says:
   If size is zero, it is identical to
 * free(ptr) and NULL is returned.

this isnt true, though it neither was before your patch in the 
CONFIG_MEMALIGN_HACK case ...


except these nitpicks iam fine with the patch

[...]
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