[Ffmpeg-devel] [BUG] put bit problem

[Michael Niedermayer]

Hi

On Sat, Mar 03, 2007 at 12:28:39PM +0100, Benjamin Larsson wrote:
> Hi, I'm using this code to pack some bits.
> 
>         PutBitContext pb;
>         GetBitContext gb;
>         init_put_bits(&pb, dst, buf_size*8);
>         init_get_bits(&gb, dst, buf_size*8);
> 
>         put_bits(&pb, 2, 2);
>         put_bits(&pb, 16, samples[0]);
>         put_bits(&pb, 6, c->status[0].step_index);
>         flush_put_bits(&pb);
> 
>         av_log(NULL,AV_LOG_INFO,"bits = %d\n", get_bits(&gb,2));
>         av_log(NULL,AV_LOG_INFO,"samples = %d\n", get_sbits(&gb,16));
>         av_log(NULL,AV_LOG_INFO,"step index = %d\n", get_bits(&gb,6));
> 
>         av_log(NULL,AV_LOG_INFO,"sample %d  step index %d\n",
> samples[0], c->status[0].step_index);
> 
> But when I run this I sometimes get the value 3 from bits.
> 
> Here follows an actual printout.
> 
> bits = 3
> samples = -22
> step index = 0
> sample -22  step index 0
> bits = 3
> samples = -85
> step index = 25
> sample -85  step index 25
> bits = 2
> samples = 304
> step index = 30
> sample 304  step index 30
> bits = 3
> samples = -1058
> step index = 32
> sample -1058  step index 32
> bits = 3
> samples = -2179
> step index = 36
> sample -2179  step index 36
> bits = 3
> samples = -197
> step index = 34
> sample -197  step index 34
> 
> 
> So to me it seems like put_bits(&pb, 2, 2) is putting incorrect bits for
> me but the others work as they should. So whats wrong with my code? I'm
> running on amd64.

you store samples as 16bit but samples is larger so it randomizes the bitwriter
state

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The greatest way to live with honor in this world is to be what we pretend
to be. -- Socrates
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