[FFmpeg-cvslog] r12144 - trunk/libavcodec/mpeg12.c

[Mike Melanson]

Rich Felker wrote:
> On Tue, Feb 19, 2008 at 04:55:14PM +0100, michael wrote:
>> Author: michael
>> Date: Tue Feb 19 16:55:14 2008
>> New Revision: 12144
>>
>> Log:
>> Reduce the number of senselessly scanned bytes.
>>
>>
>> Modified:
>>    trunk/libavcodec/mpeg12.c
>>
>> Modified: trunk/libavcodec/mpeg12.c
>> ==============================================================================
>> --- trunk/libavcodec/mpeg12.c	(original)
>> +++ trunk/libavcodec/mpeg12.c	Tue Feb 19 16:55:14 2008
>> @@ -1869,7 +1869,7 @@ static int mpeg_decode_slice(Mpeg1Contex
>>          }
>>      }
>>  eos: // end of slice
>> -    *buf += get_bits_count(&s->gb)/8 - 1;
>> +    *buf += (get_bits_count(&s->gb)-1)/8;
> 
> Have you checked what code gcc generates for this /8?? I suspect it's
> a division!! Use >>3 or fix get_bits_count to return unsigned instead
> of int.

gcc 4.1.3 on Ubuntu/x86_32 compiles the operation down to a sar
instruction. Though I agree that it's a good idea to specify bit shifts
in the interest of bit accuracy, at least for these applications.

-- 
	-Mike Melanson