Re: [libdc1394-devel] Are frames always 16 bite aligned - for fast SSE loads?

[David M. <dcm@MIT.EDU>]

Actually, the alignment of dc1394video_frame_t isn't very important
because it's just a wrapper structure.  The bytes of the frame buffer
themselves are allocated by mmap() on Mac OS X, and I couldn't find any
documentation on the alignment of that.  I'll look into it a bit more.

On Linux, the start of every frame will be 4096-byte aligned, because
they are allocated in page-sized chunks by the kernel.

Keep in mind that although the start of the images may be aligned, each
row of the image may not be aligned, depending on the number of pixels
in a row.  This may affect code that uses SIMD instructions.

-David

On Thu, 2007-02-01 at 15:38 +0100, Mark Munte wrote:
> > I don't think they are aligned. At least we are currently not doing
> > anything to ensure it.
> 
> I found out all malloc's are 16 bite aligned by default under OS X.  
> That means that as long as the size of a frame is a multiple of 16,  
> the frames will always be 16 bite aligned.
> 	capture->frames = malloc (num_dma_buffers * sizeof  
> (dc1394video_frame_t));
> Mark
> 
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