[FFmpeg-devel] [PATCH] V210 decoder and encoder

[Baptiste Coudurier]

On 5/11/2009 1:59 PM, Reimar D?ffinger wrote:
> On Mon, May 11, 2009 at 12:35:49PM -0700, Baptiste Coudurier wrote:
>> On 5/11/2009 12:27 PM, Reimar D?ffinger wrote:
>>>> +            *udst++ = (v & 0x3FF)      <<  6;
>>>> +            *ydst++ = (v & 0xFFC00)    >>  4;
>>>> +            *vdst++ = (v & 0x3FF00000) >> 14;
>>> Both
>>>
>>>> +            *udst++ = (v & 0x000003FF) <<  6;
>>>> +            *ydst++ = (v & 0x000FFC00) >>  4;
>>>> +            *vdst++ = (v & 0x3FF00000) >> 14;
>>> and
>>>
>>>> +            *udst++ = (v <<  6) & 0xFFC0;
>>>> +            *ydst++ = (v >>  4) & 0xFFC0;
>>>> +            *vdst++ = (v >> 14) & 0xFFC0;
>>> Seem nicer to me.
>> I don't get what you mean.
> 
> That I consider both alternatives more readable.
> 
>>> I think the later one might have a speed advantage due to needing only one
>>> constant.
>>> Also like in the encoder you don't really need one of the ands.
>> You mean ydst >> 14 ? What if the 2 bits are not zero ? Doesn't the bit
>> gets replicated ?
> 
> No, the << 6 one, Upper bits are dropped because udst is only 16 bits, lower
> bits 0 is shifted in. Thus the & is pointless.

I see what you mean now.

Update attached.

-- 
Baptiste COUDURIER                              GnuPG Key Id: 0x5C1ABAAA
Key fingerprint                 8D77134D20CC9220201FC5DB0AC9325C5C1ABAAA
FFmpeg maintainer                                  http://www.ffmpeg.org
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