[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 2:45 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...

-- 

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