[MPlayer-cvslog] CVS: main/libmpdemux aviheader.c,1.63,1.64

[D Richard Felker III]

On Sat, Jan 01, 2005 at 01:16:55AM -0500, D Richard Felker III wrote:
> On Fri, Dec 31, 2004 at 05:02:50PM +0100, Reimar Döffinger CVS wrote:
> > CVS change done by Reimar Döffinger CVS
> > 
> > Update of /cvsroot/mplayer/main/libmpdemux
> > In directory mail:/var2/tmp/cvs-serv30117/libmpdemux
> > 
> > Modified Files:
> > 	aviheader.c 
> > Log Message:
> > fix quicksort to avoid stack overflow and extreme runtimes
> > 
> > 
> > Index: aviheader.c
> > ===================================================================
> > RCS file: /cvsroot/mplayer/main/libmpdemux/aviheader.c,v
> > retrieving revision 1.63
> > retrieving revision 1.64
> > diff -u -r1.63 -r1.64
> > --- aviheader.c	20 Oct 2004 02:13:33 -0000	1.63
> > +++ aviheader.c	31 Dec 2004 16:02:47 -0000	1.64
> > @@ -44,15 +44,25 @@
> >      return 0;
> >  }
> >  
> > -/*
> > +/**
> >   * Simple quicksort for AVIINDEXENTRYs
> > + * To avoid too deep recursion, the bigger part is handled iteratively,
> > + * thus limiting recursion to log2(n) levels.
> > + * The pivot element is randomized to "even out" otherwise extreme cases.
> >   */
> >  static void avi_idx_quicksort(AVIINDEXENTRY *idx, int from, int to)
> >  {
> >      AVIINDEXENTRY temp;
> > -    int lo = to;
> > -    int hi = from;
> > -    off_t pivot_ofs = AVI_IDX_OFFSET(&idx[(from + to) / 2]);
> > +    int lo;
> > +    int hi;
> > +    off_t pivot_ofs;
> > +    int pivot_idx;
> > +  while (from < to) {
> > +    pivot_idx = from;
> > +    pivot_idx += rand() % (to - from + 1);
> 
> imnsho using rand() is forbidden. it corrupts the state of the caller.

not to mention, it also makes debugging hell by making the program
non-deterministic.

rich