[Libav-user] [libav-user] Using MSVC++ intrinsics

[wl2776]

I've found that when a Windows application, developed with MS Visual Studio,
uses bit-reading macros like AV_RB16, AV_RB32, etc, they are expanded to
conventional C bit operations ( >> | << &).

Inline functions av_bswapNN (where NN are numbers) are among them.

I've added some code to the libavutil/bswap.h which checks for _MSC_VER
macro and in positive case calls MSVC intrincics _byteswap_ushort,
_byteswap_ulong etc, instead of bit operations.
These intrinsics generate processor instructions, like bswap, instead of bit
operations.
http://msdn.microsoft.com/en-us/library/a3140177(v=vs.100).aspx

I wonder if it would give any benefit?

My application uses these macros to get timestamps from RTP headers and
sometimes - to parse video stream. Therefore the affect is minimal. I
could'nt see any difference in the processor load, while observed the
application in the Process Explorer.


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