lkml.org 
[lkml]   [2008]   [Jul]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] introduce lower_32_bits() macro
On Fri, 25 Jul 2008 12:06:27 -0400
"H. Peter Anvin" <hpa@zytor.com> wrote:

> Joerg Roedel wrote:
> > The file kernel.h contains the upper_32_bits macro. This patch adds the other
> > part, the lower_32_bits macro. Its first use will be in the driver for AMD
> > IOMMU.
> >
> > Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
> > ---
> > include/linux/kernel.h | 6 ++++++
> > 1 files changed, 6 insertions(+), 0 deletions(-)
> >
> > diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> > index f9cd7a5..6fd2977 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -73,6 +73,12 @@ extern const char linux_proc_banner[];
> > */
> > #define upper_32_bits(n) ((u32)(((n) >> 16) >> 16))
> >
> > +/**
> > + * lower_32_bits - return bits 0-31 of a number
> > + * @n: the number we're accessing
> > + */
> > +#define lower_32_bits(n) ((n) & 0xffffffffULL)
> > +
>
> NAK. These are assymmetric with regards to type, which is the *last*
> thing we want.

Yes, it will convert a 32-bit expression into a 64-bit one.

> The symmetric definition would be ((u32)(n)), but that's already
> idiomatic use, so why not use it as-is?

There's some readability benefit. Sometimes it is hard to understand
why some random open-coded cast was used. But I seem to recall that
there was another reason why we decided we needed this. I forget, and
so apparently did the changelog author ;)




\
 
 \ /
  Last update: 2008-07-25 22:51    [from the cache]
©2003-2011 Jasper Spaans