[FFmpeg-devel] [PATCH] Fix non-rounding up to next 16-bit aligned bug in IFF decoder

[Michael Niedermayer]

On Wed, Apr 28, 2010 at 02:23:07PM +0200, Sebastian Vater wrote:
> Sebastian Vater a ?crit :
> > I have fixed the wrong IFF decoding issue in the IFF decoder.
> >
> > The reason is that the IFF docs say that each line in the BODY chunk has
> > it's width rounded up to next 16-bit boundary, such that each new line
> > begins on a word boundary (address divisible by 2).
> >
> > Please review and apply.
> >
> > I will do the heavy optimization stuff now based on this.
> >
> >   
> Heavy optimization for decodeplane8 done. Patch attached.
> 
> Please note that I used a different IFF file for benchmarking this (one
> which was displayed incorrectly before fix non-rounding on word boundary
> patch applied).
> 
> This image also has a larger width and thus the decodeplane8 function is
> called more often per line (should yield more accurate results).
> 
> Benchmarks for fix non-rounding on word boundary patch:
> basty at cdgs-basty:~/src/ffmpeg/build$ ./ffplay ../patches/MRLake.iff
> FFplay version git-svn-r22986, Copyright (c) 2003-2010 the FFmpeg developers
>   built on Apr 28 2010 13:22:35 with gcc 4.2.4 (Ubuntu 4.2.4-1ubuntu4)
>   configuration:
>   libavutil     50.14. 0 / 50.14. 0
>   libavcodec    52.66. 0 / 52.66. 0
>   libavformat   52.61. 0 / 52.61. 0
>   libavdevice   52. 2. 0 / 52. 2. 0
>   libswscale     0.10. 0 /  0.10. 0
> [IFF @ 0x8b32790]Estimating duration from bitrate, this may be inaccurate
> Input #0, IFF, from '../patches/MRLake.iff':
>   Duration: N/A, bitrate: N/A
>     Stream #0.0: Video: iff_byterun1, pal8, 737x595, PAR 17:20 DAR
> 737:700, 90k tbr, 90k tbn, 90k tbc
> 57150 dezicycles in decodeplane8, 1 runs, 0 skips
> 55335 dezicycles in decodeplane8, 2 runs, 0 skips
> 54387 dezicycles in decodeplane8, 4 runs, 0 skips
> 53866 dezicycles in decodeplane8, 8 runs, 0 skips
> 53598 dezicycles in decodeplane8, 16 runs, 0 skips
> 53414 dezicycles in decodeplane8, 32 runs, 0 skips
> 53297 dezicycles in decodeplane8, 64 runs, 0 skips
> 53249 dezicycles in decodeplane8, 127 runs, 1 skips
> 53216 dezicycles in decodeplane8, 255 runs, 1 skips
> 53201 dezicycles in decodeplane8, 511 runs, 1 skips
> 53194 dezicycles in decodeplane8, 1023 runs, 1 skips
> 53224 dezicycles in decodeplane8, 2046 runs, 2 skips
> 53429 dezicycles in decodeplane8, 4091 runs, 5 skipsB sq=    0B f=0/0
>    0.51 A-V:  0.000 s:0.0 aq=    0KB vq=    0KB sq=    0B f=0/0   0/0
> 
> Benchmarks with heavy optimization based on fix non-rounding to word
> boundary patch:
> basty at cdgs-basty:~/src/ffmpeg/build$ ./ffplay ../patches/MRLake.iff
> FFplay version git-svn-r22986, Copyright (c) 2003-2010 the FFmpeg developers
>   built on Apr 28 2010 13:22:35 with gcc 4.2.4 (Ubuntu 4.2.4-1ubuntu4)
>   configuration:
>   libavutil     50.14. 0 / 50.14. 0
>   libavcodec    52.66. 0 / 52.66. 0
>   libavformat   52.61. 0 / 52.61. 0
>   libavdevice   52. 2. 0 / 52. 2. 0
>   libswscale     0.10. 0 /  0.10. 0
> [IFF @ 0x8b32790]Estimating duration from bitrate, this may be inaccurate
> Input #0, IFF, from '../patches/MRLake.iff':
>   Duration: N/A, bitrate: N/A
>     Stream #0.0: Video: iff_byterun1, pal8, 737x595, PAR 17:20 DAR
> 737:700, 90k tbr, 90k tbn, 90k tbc
> 24900 dezicycles in decodeplane8, 1 runs, 0 skips
> 22215 dezicycles in decodeplane8, 2 runs, 0 skips
> 19937 dezicycles in decodeplane8, 4 runs, 0 skips
> 17513 dezicycles in decodeplane8, 8 runs, 0 skips
> 16066 dezicycles in decodeplane8, 16 runs, 0 skips
> 15322 dezicycles in decodeplane8, 32 runs, 0 skips
> 14925 dezicycles in decodeplane8, 64 runs, 0 skips
> 14719 dezicycles in decodeplane8, 128 runs, 0 skips
> 14596 dezicycles in decodeplane8, 256 runs, 0 skips
> 14543 dezicycles in decodeplane8, 512 runs, 0 skips
> 14516 dezicycles in decodeplane8, 1024 runs, 0 skips
> 14503 dezicycles in decodeplane8, 2046 runs, 2 skips
> 14492 dezicycles in decodeplane8, 4093 runs, 3 skips
>    0.59 A-V:  0.000 s:0.0 aq=    0KB vq=    0KB sq=    0B f=0/0   0/0
> 
> -- 
> 
> Best regards,
>                    :-) Basty/CDGS (-:
> 

>  iff.c |   37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
> c47530e98c6fc28fa943f51b8b5d14b64cafa5c5  iff-decoder-fix-heavy-dp8.patch

just wanted to say iam still fine with this patch once its tested on
little & big & the other devels are ok with it too

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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