[FFmpeg-devel] Dirac Golomb decoder [PATCH]

[Michael Niedermayer]

Hi

On Tue, Aug 14, 2007 at 02:21:33PM +0200, Marco Gerards wrote:
> Hi,
> 
> For Dirac, some values are coded using interleaved exp. golomb.  I
> think this part of my work can already be included in FFmpeg.
> 
> In my SoC repository, you can find a program that I used to generate
> ff_interleaved_dirac_golomb_vlc_len and
> ff_interleaved_dirac_golomb_vlc_code.
> 
> Please let me know if there is something wrong with this code.
[...]

> Index: golomb.c
> ===================================================================
> --- golomb.c	(revision 10115)
> +++ golomb.c	(working copy)
> @@ -1,6 +1,7 @@
>  /*
>   * exp golomb vlc stuff
>   * Copyright (c) 2003 Michael Niedermayer <michaelni at gmx.at>
> + * Copyright (c) 2007 Marco Gerards <marco at gnu.org>
>   *

as reimar already said, we are affraid of ending up with hundreads of
copyright lines ...
if you want your name in the file, i think maybe something like

/**
 * this function finds the foobar.
 * @author (copyright) Marco Gerards <marco at gnu.org>

above functions you wrote, would be a compromise


>   * This file is part of FFmpeg.
>   *
> @@ -23,7 +24,7 @@
>   * @file golomb.c
>   * @brief
>   *     exp golomb vlc stuff
> - * @author Michael Niedermayer <michaelni at gmx.at>
> + * @author Michael Niedermayer <michaelni at gmx.at> and Marco Gerards <marco at gnu.org>
>   */
>  
>  #include "common.h"
> @@ -153,3 +154,39 @@
>    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
>    0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,
>  };
> +
> +const uint8_t ff_interleaved_dirac_golomb_vlc_len[256]={
> +9,9,7,7,9,9,7,7,5,5,5,5,5,5,5,5,
> +9,9,7,7,9,9,7,7,5,5,5,5,5,5,5,5,
> +3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> +3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> +9,9,7,7,9,9,7,7,5,5,5,5,5,5,5,5,
> +9,9,7,7,9,9,7,7,5,5,5,5,5,5,5,5,
> +3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> +3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> +1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,};

this table is identical to ff_interleaved_golomb_vlc_len


> +
> +const uint8_t ff_interleaved_dirac_golomb_vlc_code[256]={
> +0, 1, 0, 0, 2, 3, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 
> +4, 5, 2, 2, 6, 7, 3, 3, 1, 1, 1, 1, 1, 1, 1, 1, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +8, 9, 4, 4, 10,11,5, 5, 2, 2, 2, 2, 2, 2, 2, 2, 
> +12,13,6, 6, 14,15,7, 7, 3, 3, 3, 3, 3, 3, 3, 3, 
> +1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
> +1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 
> +0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,};

this looks suspiciously similar to ff_interleaved_ue_golomb_vlc_code
remove_msb(a+1) = b

could you check if svq3_get_ue_golomb() does the same as 
dirac_get_ue_golomb()?
if no please check if its maybe just that svq3 code currently doenst support
more than 32bit codewords
if they do the same, a benchmark (with actual video data) of both would be
interresting


[...]
> +        buf = GET_CACHE(re, gb);
> +
> +        buf >>= 32 - 8;

buf= SHOW_UBITS(re, gb, 8);


> +        LAST_SKIP_BITS(re, gb, FFMIN(ff_interleaved_dirac_golomb_vlc_len[buf], 8));
> +
> +        ret <<= (ff_interleaved_dirac_golomb_vlc_len[buf] - 1) >> 1;
> +        ret |= ff_interleaved_dirac_golomb_vlc_code[buf];
> +        if (ff_interleaved_dirac_golomb_vlc_len[buf] != 9)
> +            break;

this can be done more efficiently (see svq3_get_ue_golomb())
also small values should be much more common than large ones so the
loop would most of the time do just 1 iteration ...

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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