[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 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.

> 
> - Andreas
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