ALIGN MACRO understanding

While going through kernel source , I came across this ALIGN macro

#define ALIGN <http://lxr.free-electrons.com/ident?i=ALIGN>(x
<http://lxr.free-electrons.com/ident?i=x>, a
<http://lxr.free-electrons.com/ident?i=a>)             __ALIGN_KERNEL
<http://lxr.free-electrons.com/ident?i=__ALIGN_KERNEL>((x
<http://lxr.free-electrons.com/ident?i=x>), (a
<http://lxr.free-electrons.com/ident?i=a>))

and

#define __ALIGN_KERNEL
<http://lxr.free-electrons.com/ident?i=__ALIGN_KERNEL>(x
<http://lxr.free-electrons.com/ident?i=x>, a
<http://lxr.free-electrons.com/ident?i=a>)
__ALIGN_KERNEL_MASK
<http://lxr.free-electrons.com/ident?i=__ALIGN_KERNEL_MASK>(x
<http://lxr.free-electrons.com/ident?i=x>, (typeof(x
<http://lxr.free-electrons.com/ident?i=x>))(a
<http://lxr.free-electrons.com/ident?i=a>) - 1)

#define __ALIGN_KERNEL_MASK
<http://lxr.free-electrons.com/ident?i=__ALIGN_KERNEL_MASK>(x
<http://lxr.free-electrons.com/ident?i=x>, mask
<http://lxr.free-electrons.com/ident?i=mask>)    (((x
<http://lxr.free-electrons.com/ident?i=x>) + (mask
<http://lxr.free-electrons.com/ident?i=mask>)) & ~(mask
<http://lxr.free-electrons.com/ident?i=mask>))


What does this macro do? I have read this article
http://stackoverflow.com/questions/13122846/align-macro-kernel but it
was not of much help.
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