[FFmpeg-devel] [PATCH] G.729 LSF decoding

[Michael Niedermayer]

On Mon, Jun 22, 2009 at 05:38:58PM +0700, Vladimir Voroshilov wrote:
> 2009/6/22 Michael Niedermayer <michaelni at gmx.at>:
> > On Sat, Jun 20, 2009 at 02:23:07PM +0700, Vladimir Voroshilov wrote:
> >> >> ?g729data.h | ? 11 +++++++++
> >> >> ?g729dec.c ?| ? 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >> ?2 files changed, 81 insertions(+)
> >> >> 180ee12ea9d2d6990454e9bc3a25d29828c2e0b2 ?0001-LSF-decoding-routines.161.patch
> >> >> From e2e6b6b18255c9d24f9cc0cf60dfbd1c4ccbcef1 Mon Sep 17 00:00:00 2001
> >> >> From: Vladimir Voroshilov <voroshil at gmail.com>
> >> >> Date: Sat, 6 Jun 2009 08:00:56 +0700
> >> >> Subject: [PATCH] LSF decoding routines
> >> >>
> >> >>
> >> >> diff --git ffmpeg-r19218/libavcodec/g729data.h ffmpeg-r19218_v161/libavcodec/g729data.h
> >> >> index 796d24e..587db67 100644
> >> >> --- ffmpeg-r19218/libavcodec/g729data.h
> >> >> +++ ffmpeg-r19218_v161/libavcodec/g729data.h
> >> >> @@ -262,4 +262,15 @@ static const int16_t cb_ma_predictor[2][MA_NP][10] = { /* (0.15) */
> >> >> ? ? ?{ 3024, ?1592, ? 940, ?1631, ?1723, ?1579, ?2034, ?2084, ?1913, ?2601}
> >> >> ? ?}
> >> >> ?};
> >> >> +
> >> >> +/**
> >> >> + * ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 3
> >> >> + * ff_g720_cb_ma_predictor_sum[j][i] = ?1 - sum ( ff_g729_cb_ma_predictor[k][i] ), j=0..1, i=0..9
> >> >> + * ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?k=0
> >> >> + */
> >> >
> >> > this doesnt look correct
> >>
> >> It does in floating-point.
> >
> > no it does not, this formula is not correct and this is not a matter of
> > scaling some constant
> >
> >
> >> I've changed "1" to "32765" (now it is correct for fixed-point) and added notice
> >> why values may slightly differ in array and formula.
> >
> > I think ive said it many month ago already but if you cannot write
> > documentation that matches the code then do NOT write documentation. Wrong
> > documentation is far worse than no documentation.
> >
> > first, this set all entries [j][i] for j=0..1, i=0..9, but j is never
> > used in the formula, still [0][i] is very different from [1][i], thats not
> > just sloppy, then you used constants like 1 instead of 32765 thats also not
> > a little off
> 
> Yes, i really missed third dimension at right side.
> With below formula i get about +/-1 differences between formula and
> table values.
> 
>                                            3
> ff_g720_cb_ma_predictor_sum[j][i] =  32765 - sum (
> ff_g729_cb_ma_predictor[j][k][i] ), j=0..1, i=0..9
>                                           k=0
> 
> > and finally it still doesnt match the table and your solution is just adding
> > a note saying that initial calculation was done in floating point, what is
> > that supposed to mean? Is summing 16bit values in float giving differnt
> > results than integers for you? what kind of cpu is that?
> 
> I'm afraid you don't understand me.
> Imagine there is some array  X[N] (floating-point). S=sum(X[n])
> and there is another array X_fp[N] (foxed-point) X_fp[n]= X[n] * FP_BASE
> S_fp=sum(X_fp[n])
> 
> I just wanted to say that S and S_fp in above sample can slightly differ.

what you wrote in the doxy was
"Values in array may slightly differ, since initial calculation was done in floating-point."

this is totally backward, you KNOW they differ and i suspect you have no
faint clue if any calculations where done in floating point by the ITU
comitee to build these tables.

That would make it a
"Values do differ slightly, we do not know why"

If OTOH you do know how ITU build these tables then this should be in the
doxy not a formlar that differs by +-2 or something.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20090622/1a407235/attachment.pgp>