[theora-dev] bitpack.c odditiy

Nils Pipenbrinck n.pipenbrinck at cubic.org
Tue Dec 16 11:17:16 PST 2008

Timothy B. Terriberry wrote:
> Nils Pipenbrinck <n.pipenbrinck at cubic.org> wrote:
>> While browsing the code I came across line 83 bitpack.c:
>>   *_ret=((ret&0xFFFFFFFFUL)>>(m>>1))>>(m+1>>1);
>> Is there any reason why this is so convoluted? Maybe endianess or 64 bit
>> issues? If I'm not mistaken it does exactly the the same as:
>>   *_ret = ret >> m;
> Yes, there is. 64-bit issues, as you noted, require the mask. It  
> should be optimized out by a 32-bit compiler. However, m can take the  
> full range of values from 0 to 32. 

Ah! It shifts by 32 as well. Now it all makes sense and it's very clever 
as well.

Thanks for the explanation.


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