[FFmpeg-devel] [PATCH] avcodec/alsdec: implement floating point decoding

[Umair Khan]

On Tue, Jul 19, 2016 at 3:08 AM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Mon, Jul 18, 2016 at 11:42:48PM +0530, Umair Khan wrote:
>> On Sun, Jul 17, 2016 at 3:38 PM, Michael Niedermayer
>> <michael at niedermayer.cc> wrote:
>> > On Sun, Jul 17, 2016 at 11:54:49AM +0200, Michael Niedermayer wrote:
>> >> On Sun, Jul 17, 2016 at 09:00:48AM +0530, Umair Khan wrote:
>> >> > Hi,
>> >> >
>> >> > On Sun, Jul 17, 2016 at 12:25 AM, Thilo Borgmann <thilo.borgmann at mail.de> wrote:
>> >> > > Hi,
>> >> > >
>> >> > >> From 70e65b26cc3f84c9c664c30808b43a5e1cf16eaa Mon Sep 17 00:00:00 2001
>> >> > >> From: Umair Khan <omerjerk at gmail.com>
>> >> > >> Date: Sat, 16 Jul 2016 23:52:39 +0530
>> >> > >> Subject: [PATCH 1/1] avcodec/alsdec: implement floating point decoding
>> >> > >>
>> >> > >> It conforms to RM22 version of the reference codec.
>> >> > >>
>> >> > >> Signed-off-by: Umair Khan <omerjerk at gmail.com>
>> >> > >> ---
>> >> > >>  libavcodec/Makefile           |   2 +-
>> >> > >>  libavcodec/alsdec.c           | 284 +++++++++++++++++++++++++++++++++++++++++-
>> >> > >>  libavcodec/mlz.c              | 171 +++++++++++++++++++++++++
>> >> > >>  libavcodec/mlz.h              |  69 ++++++++++
>> >> > >>  libavutil/softfloat_ieee754.h | 115 +++++++++++++++++
>> >> > >>  5 files changed, 638 insertions(+), 3 deletions(-)
>> >> > >>  create mode 100644 libavcodec/mlz.c
>> >> > >>  create mode 100644 libavcodec/mlz.h
>> >> > >>  create mode 100644 libavutil/softfloat_ieee754.h
>> >> > >>
>> >> > >> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
>> >> > >> index abef19e..a03adf5 100644
>> >> > >> --- a/libavcodec/Makefile
>> >> > >> +++ b/libavcodec/Makefile
>> >> > >> @@ -163,7 +163,7 @@ OBJS-$(CONFIG_ALAC_DECODER)            += alac.o alac_data.o alacdsp.o
>> >> > >>  OBJS-$(CONFIG_ALAC_ENCODER)            += alacenc.o alac_data.o
>> >> > >>  OBJS-$(CONFIG_ALIAS_PIX_DECODER)       += aliaspixdec.o
>> >> > >>  OBJS-$(CONFIG_ALIAS_PIX_ENCODER)       += aliaspixenc.o
>> >> > >> -OBJS-$(CONFIG_ALS_DECODER)             += alsdec.o bgmc.o mpeg4audio.o
>> >> > >> +OBJS-$(CONFIG_ALS_DECODER)             += alsdec.o bgmc.o mlz.o mpeg4audio.o
>> >> > >>  OBJS-$(CONFIG_AMRNB_DECODER)           += amrnbdec.o celp_filters.o   \
>> >> > >>                                            celp_math.o acelp_filters.o \
>> >> > >>                                            acelp_vectors.o             \
>> >> > >> diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
>> >> > >> index a7e58a2..c710fc3 100644
>> >> > >> --- a/libavcodec/alsdec.c
>> >> > >> +++ b/libavcodec/alsdec.c
>> >> > >> @@ -35,8 +35,11 @@
>> >> > >>  [...]
>> >> > >>
>> >> > >> +/** multiply two softfloats and handle the rounding off
>> >> > >> + */
>> >> > >> +static SoftFloat_IEEE754 multiply(SoftFloat_IEEE754 a, SoftFloat_IEEE754 b) {
>> >> > >> [...]
>> >> > >
>> >> > > Why is this in alsdec.c?
>> >> >
>> >> > This is not the actual IEEE 754 multiplication. It is as is mentioned
>> >> > in the reference spec.
>> >> > The typical one for 754 floats, I've implemented here separately -
>> >> > https://github.com/omerjerk/FFmpeg/commit/d6cd4bf66b9da46dd87580d7d974ce44abdcfba2#diff-4dd4b2d8d523f336fbefa96e9252187cR93
>> >> >
>> >> > > [...]
>> >> > >
>> >> > >> diff --git a/libavcodec/mlz.c b/libavcodec/mlz.c
>> >> > >> new file mode 100644
>> >> > >> index 0000000..cb2ed6a
>> >> > >> --- /dev/null
>> >> > >> +++ b/libavcodec/mlz.c
>> >> > >> [...]
>> >> > >
>> >> > >> +static int input_code(GetBitContext* gb, int len) {
>> >> > >> +    int tmp_code = 0;
>> >> > >> +    int i;
>> >> > >> +    for (i = 0; i < len; ++i) {
>> >> > >> +        tmp_code += get_bits1(gb) << i;
>> >> > >> +    }
>> >> > >> +    return tmp_code;
>> >> > >> +}
>> >> > >
>> >> > > Is there nothing in get_bits.h that solves that already?
>> >> > >
>> >> > > -Thilo
>> >> >
>> >> > I'm not sure. It is just reading the bits in the reverse order. May be
>> >> > someone else can help.
>> >>
>> >> theres asv2_get_bits()
>> >> if it works here it could be shared
>> >
>> > note though asv2_get_bits() is maximum 8 bits, for more bits more
>> > table lookups or a bigger table is needed
>>
>> What should be the best way to use this function? It is not present in
>> any header file.
>
> it could be moved into a header and made static inlinw with a more
> generic name.
> That is if it works ...

I did this for now and it doesn't seem to read the reversed bits properly.
https://github.com/omerjerk/FFmpeg/commit/c58bdd74518444022c753e24d8048e2fd9febd72

No idea what's wrong. If it was reversing the bits properly, this code
should've worked I guess.

-Umair