[FFmpeg-devel] lavf/matroska*: add support for signed integers

[Michael Niedermayer]

On Fri, Nov 15, 2013 at 11:28:21AM +0100, Jan Gerber wrote:
> 
> On 11/14/2013 10:53 PM, Michael Niedermayer wrote:
> > 
> > if i try the example from http://matroska.org/technical/specs/index.html
> > 0xFE & 0x80
> >     negative = 1
> >     0x7E
> > 
> > if(negative)
> >     num = 0 - 0x7E
> > 
> > this does nt seem to reach the expected -2 which is 0xFE
> > 
> > but maybe iam missing something
> > 
> 
> good catch, fixed version attached.
> 
> ---
>  libavformat/matroskadec.c | 27 +++++++++++++++++++++++++++
>  libavformat/matroskaenc.c | 21 +++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> 

[...]

> @@ -759,6 +760,31 @@ static int ebml_read_uint(AVIOContext *pb, int size, uint64_t *num)
>  }
>  
>  /*
> + * Read the next element as a signed int.
> + * 0 is success, < 0 is failure.
> + */
> +static int ebml_read_sint(AVIOContext *pb, int size, int64_t *num)
> +{
> +    int n = 0;
> +
> +    if (size > 8)
> +        return AVERROR_INVALIDDATA;
> +
> +    *num = avio_r8(pb);
> +    if (*num & 0x80) {
> +        *num = -1;
> +    } else {
> +        *num = 0;
> +    }

this discards the 7 less significant bits
i think these contain bits from the number to be read

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Avoid a single point of failure, be that a person or equipment.
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