what is the effect of RADEON_ALIGN (macros) in ATI-driver?

[Cui, Hunk]

Hi, guys,
 In ATI-driver -> Radeon.h -> line 254:
http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/tree/src/radeon.h
#n254

	What is the effect of RADEON_ALIGN (macros)? Now I am
investigating how to calculate the video overlay size in Geode driver,
as the website link:
http://cgit.freedesktop.org/xorg/driver/xf86-video-geode/tree/src/lx_vid
eo.c#n223 

	But I'm confused by the code, not really sure of the calculate:
YDstPitch = (width + 31) & ~31; & UVDstPitch = ((width >> 1) + 15) &
~15;

	I found they have similar principle with RADEON_ALIGN (macros),
so I want to exactly know the effect. I hope you can give me some
suggestion and hints. :)

Thanks
Hunk Cui