[FFmpeg-devel] [PATCH v1 6/6] avfilter/vf_random: seeds is uint32, it's enough to use int32_t

[Limin Wang]

On Fri, Oct 11, 2019 at 07:34:00AM +0000, Andreas Rheinhardt wrote:
> Limin Wang:
> > On Fri, Oct 11, 2019 at 06:59:00AM +0000, Andreas Rheinhardt wrote:
> >> Limin Wang:
> >>> On Fri, Oct 11, 2019 at 06:20:00AM +0000, Andreas Rheinhardt wrote:
> >>>> lance.lmwang at gmail.com:
> >>>>> From: Limin Wang <lance.lmwang at gmail.com>
> >>>>>
> >>>>> Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> >>>>> ---
> >>>>>  libavfilter/vf_random.c | 2 +-
> >>>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/libavfilter/vf_random.c b/libavfilter/vf_random.c
> >>>>> index 1937eae771..9f2153be61 100644
> >>>>> --- a/libavfilter/vf_random.c
> >>>>> +++ b/libavfilter/vf_random.c
> >>>>> @@ -33,7 +33,7 @@ typedef struct RandomContext {
> >>>>>  
> >>>>>      AVLFG lfg;
> >>>>>      int nb_frames;
> >>>>> -    int64_t random_seed;
> >>>>> +    int32_t random_seed;
> >>>>>      int nb_frames_filled;
> >>>>>      AVFrame *frames[MAX_FRAMES];
> >>>>>      int64_t pts[MAX_FRAMES];
> >>>>>
> >>>>     { "seed",   "set the seed",                  OFFSET(random_seed),
> >>>> AV_OPT_TYPE_INT64, {.i64=-1}, -1, UINT32_MAX, FLAGS },
> >>>>
> >>>> So in addition to the complete range of an uint32_t one also needs
> >>>> another value that instructs init to get a random seed of its own.
> >>>
> >>> yes, the max range is UINT32_MAX, so no need to use int64_t
> >>>
> >> First of all, simply changing the value to 32 bit is not right -- you
> >> would also have to change the type in the corresponding AVOption (it
> > 
> > I haven't see .i32 type for AVOption
> > 
> >> might seem to work on little-endian systems, but it certainly doesn't
> >> on big-endian systems; actually using -1 as random_seed would probably
> >> already not work on little-endian systems either). Second, there are
> >> more legal values for random_seed than values representable in 32 bit,
> >> hence one has to use a type with more than 32 bit.
> > 
> > random_seed = -1, it'll get the seed by av_get_random_seed(), it'll
> > return 32bit.
> > 
> > else 
> > 
> > uint32_t seed
> >      seed = s->random_seed;
> >      av_lfg_init(&s->lfg, seed);
> > 
> > the seed is uint32_t still, so user can't use with more than 32bit
> > for the current code.
> > 
> There are more than 2^32 legal values the user can input for
> random_seed: The 2^32 values which should be directly used as random
> seed and the special value -1. You need a type with more than 32 bits
> to distinguish -1 from UINT32_MAX.

OK, thanks for reviewing and feedback, I haven't think it too much at
first, let keep it 64bit anyway.

> 
> - Andreas
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