[FFmpeg-devel] [PATCH] MMX/floating-point crash issue

[Ray Simard]

Forgot to attach the patch...


On 1/11/2012 10:18 PM, Ray Simard wrote:
> The following requires the patch for the uninitialized variable above to
> be applied first ("Odd, random-appearing crashes"), so I'm mentioning
> this here, after that.
> 
> As Reimar Doeffinger pointed out, there is no reason to use doubles in
> these loops. As it happens, the result is worse than needless overhead;
> the assignment of the result of the MMX calculations called by the CMP
> macro to the double floating-point members of mv without an intervening
> call to emms_c() was causing bogus data to be assigned, resulting in the
> crashes. In fact, the values in mv are never used for anything except
> integer values.
> 
> (My earlier, rather naive suggestion, to add emms_c() calls in the
> loops, should be disregarded.  It was a good test to verify the cause of
> the data-corruption and crash problem, but not a solution.)
> 
> The attached patch implements his suggestion to replace the MotionVector
> variables in these cases with an integer-only version. I've tried it out
> and it seems to be working perfectly.  At the moment I'm running FATE on
> it. It's very straightforward and I'd be very surprised if there were
> any problem with it.
> 
> 
> Note: This does not affect the MotionVector member of the Transform
> struct passed to avfilter_transform(). That is still double.
> Determining whether or not that should also be changed requires further
> scrutiny.
> 
> 
> One of the loops in question. Others are similar. The struct mv points
> to was a MotionVector struct in which x and y were double.
> 
>     if (deshake->search == EXHAUSTIVE) {
>         // Compare every possible position - this is sloooow!
>         for (y = -deshake->ry; y <= deshake->ry; y++) {
>             for (x = -deshake->rx; x <= deshake->rx; x++) {
>                 diff = CMP(cx - x, cy - y);
>                 if (diff < smallest) {
>                     smallest = diff;
>                     mv->x = x;  <=== BOGUS.
>                     mv->y = y;  <===  ""
>                 }
>             }
>         }
> 
> Ray Simard
> rhs.ffmpeg at sylvan-glade.com
> 
> 
> _______________________________________________
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> ffmpeg-devel at ffmpeg.org
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> 
> 


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