[FFmpeg-devel] [PATCH] Optimization of original IFF codec

[Sebastian Vater]

Hi Michael!

Michael Niedermayer a ?crit :
> On Sun, Apr 25, 2010 at 01:49:54PM +0200, Sebastian Vater wrote:
>   
>>> that loop then can be unrolled by a factor of 4 and its inside for the
>>> uint8_t type case be implemented like:
>>>     v= lut[get_bits(&gb, 4)];
>>>     AV_WN32A(dst+b, AV_RN32A(dst+b) | v);
>>>   
>>>       
>> The thing is that type can be both uint8_t and uint32_t. It's a #define
>> macro which gets the type (uint8_t or uint32_t) passed by.
>>
>> So not fixed yet because I'm unsure here, if those two lines can be done
>> with dst being uint32_t also.
>>     
>
> they can, and it will speed the uint8 case up significantly
>   
When I understand you right, I have to create a lookup table the
following way:
For each of the 4-pair read bits:
{0000 = 0, 0001 = 1 << plane, 0010 = 0x100 << plane, 0011 = (1 << plane)
| (0x100 << plane), 0100 = (0x10000 << plane), ...}

Is that correct?

-- 

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