[FFmpeg-devel] [PATCH] HAM6/HAM8 support for IFF demuxer/decoder

[Sebastian Vater]

Alex Converse a ?crit :
> On Thu, May 6, 2010 at 11:52 AM, Sebastian Vater
> <cdgs.basty at googlemail.com> wrote:
>   
> +/**
> + * Puts an uint8_t/uint16_t/uint32_t/uint64_t value using big endian mode
> + * if, and only if the extradata context is allocated
> + */
> +#define PUT_EXCTX_INT8(x,offset,v)  if ((x) != NULL)
>              \
> +                                       (((uint8_t *) (x))[(offset)] = (v))
> +#define PUT_EXCTX_INT16(x,offset,v) if ((x) != NULL)
>              \
> +                                       AV_WB16(((uint8_t *) (x)) +
> (offset), (v))
> +#define PUT_EXCTX_INT32(x,offset,v) if ((x) != NULL)
>              \
> +                                       AV_WB32(((uint8_t *) (x)) +
> (offset), (v))
> +#define PUT_EXCTX_INT64(x,offset,v) if ((x) != NULL)
>              \
> +                                       AV_WB64(((uint8_t *) (x)) +
> (offset), (v))
> +
>
> What do these macros actually accomplish? They are only used where x
> is already uint8_t and not null.
>   

They should be!

x is NULL if the extradata context isn't available, i.e. if an old IFF
demuxer is used in combination with the current new IFF decoder.

In this case the old IFF demuxer just allocates (1 << number of
bitplanes) * 3 bytes. Since maximum number of planes is 8, that will be
256*3 = 768 bytes.

The GET_EXTRA_CONTEXT(x) checks if the extradata is at least 1 KB (to
make sure there's not only the palette data like it happened in old
versions) and returns NULL if there's no other extradata.
Since I'm using uint8_t *ex = GET_EXTRA_CONTEXT(avctx) for example, that
will return NULL to ex.

The PUT/GET macros just check whether if the context is available (by
comparing ex to non-NULL) and do the appreciate action if that's the
case, otherwise GET returns always 0).

PUT will simply do nothing if ex is NULL.

-- 

Best regards,
                   :-) Basty/CDGS (-: