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Re: [MPlayer-dev-eng] [PATCH] Remove needless memsets after calloc




Hi Michael!

On 2018-01-01 13:39 -0500, Michael McConville wrote:
> 
> Unless, I’m missing something obvious, this is pretty self-explanatory.

You are not missing anything AFAICT.

Seem to be oversights from SVN commit r18559 , but they may
be security relevant. I cannot say for sure, because I did
not fully analyze these code paths and all possible memset
implementations.

Either way I believe it's better to remove those memset calls.

Committed your patch.


>Calloc zeroes memory, so there’s no need to re-zero it, and modern compilers often miss this optimization.

From a quick glance, those don't seem important for performance.


Thank you for your contribution!

  Alexander

> Index: libmpdemux/muxer_avi.c
> ===================================================================
> --- libmpdemux/muxer_avi.c	(revision 38012)
> +++ libmpdemux/muxer_avi.c	(working copy)
> @@ -120,7 +120,6 @@
>      si->idx=calloc(si->idxsize, sizeof(struct avi_odmlidx_entry));
>      si->riffofssize=16;
>      si->riffofs=calloc((si->riffofssize+1), sizeof(off_t));
> -    memset(si->riffofs, 0, sizeof(off_t)*si->riffofssize);
>  
>      switch(type){
>      case MUXER_TYPE_VIDEO:
> @@ -619,7 +618,6 @@
>  
>      si->superidxsize = si->superidxpos;
>      si->superidx = calloc(si->superidxsize, sizeof(*si->superidx));
> -    memset(si->superidx, 0, sizeof(*si->superidx) * si->superidxsize);
>  
>      idxpos = 0;
>      for (j=0; j<si->superidxpos; j++) {
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