[FFmpeg-devel] [RFC] mixed-endian get_bits

[Reimar Döffinger]

On Thu, Sep 30, 2010 at 08:40:41PM +0100, M?ns Rullg?rd wrote:
> Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> > this patch would, when ALT_BITSTREAM_READER is defined, provide an
> > alternative get_bits_le that behaves as the get_bits when
> > ALT_BITSTREAM_READER_LE is defined.
> > This is a hack that is due to the fact the GSM 06.10 and the MS
> > variant use different bitstream layouts.
> > The best idea I had without bloating neither code nor binary size
> > involes using this as in attached patch.
> > There are a lot of other ways to do this of course (manually parsing
> > the bitstream like other GSM decoders do certainly is not one I'd
> > consider good though).
> 
> Why not simply split out the parts needing two versions and compile
> twice with different existing bitstream readers?

Well, that would be a call overhead of 9 calls per 33 decoded bytes.
Not really a big deal for this codec, and one of the many other
possibilities I thought about.
I mostly picked this one because it was
1) really quick to implement
2) most interesting (whether that's good or bad I leave up to you :-) ).

I always very much disliked that with get_bits you had to decide on
one bitstream format and that would be the only one you could use
throughout the whole file.
It also has the side-effect that it's a huge pain (if possible) to
move anything from get_bits.h into a header (e.g. things that are not
at all performance-critical).