Messages in this thread | | | Date | Fri, 25 Jul 2008 13:47:59 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] introduce lower_32_bits() macro |
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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 ;)
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