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

Sebastian Vater vater
Thu Apr 29 23:34:10 CEST 2010


Sebastian Vater a ?crit :
> Ronald S. Bultje a ?crit :
>   
>> Hi,
>>
>> On Thu, Apr 29, 2010 at 2:45 PM, Sebastian Vater
>> <cdgs.basty at googlemail.com> wrote:
>>   
>>     
>>> Did another version:
>>>     
>>>       
>> [..]
>>   
>>     
>>>    START_TIMER;
>>>    const uint32_t *lut = plane8_lut[plane];
>>>    for(; --buf_size != 0; dst += 8) {
>>>        uint32_t v;
>>>        const unsigned x = *buf++;
>>>        v = AV_RN32A(dst) | lut[x >> 4];
>>>        AV_WN32A(dst, v);
>>>        v = AV_RN32A(dst + 4) | lut[x & 0x0F];
>>>        AV_WN32A(dst + 4, v);
>>>    }
>>>    STOP_TIMER("decodeplane8");
>>>     
>>>       
>> [..]
>>   
>>     
>>>      58:       0f b6 16                movzbl (%esi),%edx
>>>      5b:       83 c6 01                add    $0x1,%esi
>>>      5e:       89 d0                   mov    %edx,%eax
>>>      60:       83 e2 0f                and    $0xf,%edx
>>>      63:       c1 e8 04                shr    $0x4,%eax
>>>      66:       8b 04 87                mov    (%edi,%eax,4),%eax
>>>      69:       09 01                   or     %eax,(%ecx)
>>>      6b:       8b 04 97                mov    (%edi,%edx,4),%eax
>>>      6e:       09 41 04                or     %eax,0x4(%ecx)
>>>      71:       83 c1 08                add    $0x8,%ecx
>>>      74:       83 eb 01                sub    $0x1,%ebx
>>>      77:       75 df                   jne    58 <decodeplane8+0x58>
>>>     
>>>       
>> [..]
>>   
>>     
>>> 9067 dezicycles in decodeplane8, 32 runs, 0 skips
>>> 8562 dezicycles in decodeplane8, 64 runs, 0 skips
>>> 8318 dezicycles in decodeplane8, 128 runs, 0 skips
>>> 8195 dezicycles in decodeplane8, 256 runs, 0 skips
>>> 8132 dezicycles in decodeplane8, 512 runs, 0 skips
>>> 8096 dezicycles in decodeplane8, 1023 runs, 1 skips
>>> 8077 dezicycles in decodeplane8, 2046 runs, 2 skips
>>> 8070 dezicycles in decodeplane8, 4094 runs, 2 skips
>>>     
>>>       
>> That looks good to me.
>>   
>>     
>
> Using uint64_t again with 8-bit lut:
> /**
>  * Decode interleaved plane buffer up to 8bpp
>  * @param dst Destination buffer
>  * @param buf Source buffer
>  * @param buf_size
>  * @param bps bits_per_coded_sample (must be <= 8)
>  * @param plane plane number to decode as
>  */
> static void decodeplane8(uint8_t *dst,
>                          const uint8_t *buf,
>                          unsigned buf_size,
>                          const unsigned bps,
>                          const unsigned plane)
> {
>     START_TIMER;
>     const uint64_t *lut = plane8_lut[plane];
>     for(; --buf_size != 0; dst += 8) {
>         const uint64_t v = AV_RN64A(dst) | lut[*buf++];
>         AV_WN64A(dst, v);
>     }
>     STOP_TIMER("decodeplane8");
> }
>
>       58:       8b 54 24 64             mov    0x64(%esp),%edx
>       5c:       8b 4c 24 44             mov    0x44(%esp),%ecx
>       60:       8b 5d 04                mov    0x4(%ebp),%ebx
>       63:       8b 45 00                mov    0x0(%ebp),%eax
>       66:       0f b6 32                movzbl (%edx),%esi
>       69:       83 44 24 64 01          addl   $0x1,0x64(%esp)
>       6e:       8b 54 f1 04             mov    0x4(%ecx,%esi,8),%edx
>       72:       0b 04 f1                or     (%ecx,%esi,8),%eax
>       75:       09 da                   or     %ebx,%edx
>       77:       89 45 00                mov    %eax,0x0(%ebp)
>       7a:       89 55 04                mov    %edx,0x4(%ebp)
>       7d:       83 c5 08                add    $0x8,%ebp
>       80:       83 ef 01                sub    $0x1,%edi
>       83:       75 d3                   jne    58 <decodeplane8+0x58>
>
> Benchmark results:
> basty at cdgs-basty:~/src/ffmpeg/build$ ./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 @ 0x8b33790]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
> 40560 dezicycles in decodeplane8, 1 runs, 0 skips
> 35145 dezicycles in decodeplane8, 2 runs, 0 skips
> 23632 dezicycles in decodeplane8, 4 runs, 0 skips
> 17127 dezicycles in decodeplane8, 8 runs, 0 skips
> 11680 dezicycles in decodeplane8, 16 runs, 0 skips
> 8965 dezicycles in decodeplane8, 32 runs, 0 skips
> 7628 dezicycles in decodeplane8, 64 runs, 0 skips
> 6939 dezicycles in decodeplane8, 128 runs, 0 skips
> 6565 dezicycles in decodeplane8, 256 runs, 0 skips
> 6385 dezicycles in decodeplane8, 512 runs, 0 skips
> 6290 dezicycles in decodeplane8, 1024 runs, 0 skips
> 6246 dezicycles in decodeplane8, 2048 runs, 0 skips
> 6224 dezicycles in decodeplane8, 4096 runs, 0 skips
>    1.94 A-V:  0.000 s:0.0 aq=    0KB vq=    0KB sq=    0B f=0/0   0/0
>
> Way faster, but when I look at the code I wonder why...probably because
> it handles pipeline stalling much better...
>   
I have attached the uint64_t patch. Please review it!

The 8-bit table declaration looks a little bit long...

-- 

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

Es ist keine Kunst, ein besseres Produkt als Microsoft zu entwickeln,
es ist eine Kunst, schlechteres zu programmieren...
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