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

[Sebastian Vater]

Ronald S. Bultje a ?crit :
> Hi,
>
> On Thu, Apr 29, 2010 at 2:22 PM, Sebastian Vater
> <cdgs.basty at googlemail.com> wrote:
>   
>> Regarding your idea gcc outputs:
>>      52:       0f b6 16                movzbl (%esi),%edx
>>      55:       83 c6 01                add    $0x1,%esi
>>      58:       89 d0                   mov    %edx,%eax
>>      5a:       83 e2 0f                and    $0xf,%edx
>>      5d:       c1 e8 04                shr    $0x4,%eax
>>      60:       8b 04 81                mov    (%ecx,%eax,4),%eax
>>      63:       09 03                   or     %eax,(%ebx)
>>      65:       8b 04 91                mov    (%ecx,%edx,4),%eax
>>      68:       09 43 04                or     %eax,0x4(%ebx)
>>      6b:       83 c3 08                add    $0x8,%ebx
>>      6e:       39 df                   cmp    %ebx,%edi
>>      70:       77 e0                   ja     52 <decodeplane8+0x52>
>>     
>
> 12 instructions, so 2 less, as intended. Is it faster?
>   

Old method:
basty at cdgs-basty:~/src/ffmpeg/build$ ./ffplay ../patches/MRLake.iff
FFplay version git-5b9f10d, Copyright (c) 2003-2010 the FFmpeg developers
  built on Apr 29 2010 15:19:11 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
18270 dezicycles in decodeplane8, 1 runs, 0 skips
14805 dezicycles in decodeplane8, 2 runs, 0 skips
12340 dezicycles in decodeplane8, 4 runs, 0 skips
11127 dezicycles in decodeplane8, 8 runs, 0 skips
9640 dezicycles in decodeplane8, 16 runs, 0 skips
8882 dezicycles in decodeplane8, 32 runs, 0 skips
8496 dezicycles in decodeplane8, 64 runs, 0 skips
8312 dezicycles in decodeplane8, 127 runs, 1 skips
8220 dezicycles in decodeplane8, 255 runs, 1 skips
8173 dezicycles in decodeplane8, 511 runs, 1 skips
8149 dezicycles in decodeplane8, 1023 runs, 1 skips
8135 dezicycles in decodeplane8, 2046 runs, 2 skips
8128 dezicycles in decodeplane8, 4093 runs, 3 skips
   0.76 A-V:  0.000 s:0.0 aq=    0KB vq=    0KB sq=    0B f=0/0   0/0

New method with 2 instructions less:
basty at cdgs-basty:~/src/ffmpeg/build$ ./ffplay ../patches/MRLake.iff
FFplay version git-5b9f10d, Copyright (c) 2003-2010 the FFmpeg developers
  built on Apr 29 2010 15:19:11 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
16180 dezicycles in decodeplane8, 1 runs, 0 skips
14210 dezicycles in decodeplane8, 2 runs, 0 skips
12887 dezicycles in decodeplane8, 4 runs, 0 skips
10575 dezicycles in decodeplane8, 8 runs, 0 skips
9363 dezicycles in decodeplane8, 16 runs, 0 skips
8755 dezicycles in decodeplane8, 32 runs, 0 skips
8445 dezicycles in decodeplane8, 64 runs, 0 skips
8288 dezicycles in decodeplane8, 128 runs, 0 skips
8208 dezicycles in decodeplane8, 256 runs, 0 skips
8185 dezicycles in decodeplane8, 512 runs, 0 skips
8162 dezicycles in decodeplane8, 1024 runs, 0 skips
8148 dezicycles in decodeplane8, 2048 runs, 0 skips
8145 dezicycles in decodeplane8, 4095 runs, 1 skips
   3.84 A-V:  0.000 s:0.0 aq=    0KB vq=    0KB sq=    0B f=0/0   0/0

The new method is initially faster but is 0,01% slower at the end...

Remember, I'm back at home again, so these benchmarks are again Athlon
XP+ 2100,  so please don't compare them with the ones I did on the
Pentium 4.

-- 

Best regards,
                   :-) Basty/CDGS (-: