[FFmpeg-cvslog] r24102 - trunk/libavutil/random_seed.c

[Michael Niedermayer]

On Thu, Jul 08, 2010 at 12:58:23AM +0100, M?ns Rullg?rd wrote:
> michael <subversion at mplayerhq.hu> writes:
> 
> > Author: michael
> > Date: Thu Jul  8 01:47:48 2010
> > New Revision: 24102
> >
> > Log:
> > get_generic_seed() for the cases without /dev/random and AV_READ_TIME
> 
> Thanks.
> 
> > Modified:
> >    trunk/libavutil/random_seed.c
> >
> > Modified: trunk/libavutil/random_seed.c
> > ==============================================================================
> > --- trunk/libavutil/random_seed.c	Thu Jul  8 01:41:42 2010	(r24101)
> > +++ trunk/libavutil/random_seed.c	Thu Jul  8 01:47:48 2010	(r24102)
> > @@ -21,6 +21,7 @@
> >  #include <unistd.h>
> >  #include <fcntl.h>
> >  #include "timer.h"
> > +#include "time.h"
> >  #include "random_seed.h"
> >  #include "avutil.h"
> >
> > @@ -37,6 +38,38 @@ static int read_random(uint32_t *dst, co
> >      return err;
> >  }
> >
> > +static uint32_t get_generic_seed(void)
> > +{
> > +    int last_t=0;
> > +    int bits=0;
> > +    uint64_t random=0;
> > +    int i;
> > +    int s=0;
> > +
> > +    for(i=0;bits<64;i++){
> > +        int t= clock()>>s;
> 
> What about systems without a functioning clock() call?  This is
> allowed by the specs:
> 
>   If the processor time used is not available or its value cannot be
>   represented, the function shall return the value (clock_t)-1.
> 
> If clock() always returns -1, this loop will run forever.

what else is giving us reasonable precission (1 tick per second would
need 2 minutes per seed) and is portable?


> 
> > +        if(last_t && t != last_t){
> > +            if(i<10000U && s<24){
> 
> Why the U suffix?

for unsigned compare, otherwise if i becomes negative this could behave odd

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is not what we do, but why we do it that matters.
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