On Tue, 11 Nov 2008 11:04:54 +0100 Jean Delvare <khali at linux-fr.org> wrote:
> Hi Darrick,
>
> On Mon, 10 Nov 2008 17:01:32 -0800, Darrick J. Wong wrote:
> >
> > Create a helper macro to divide two numbers and round the result to the
> > nearest whole number. This is a helper macro for hwmon drivers that
> > want to convert incoming sysfs values per standard hwmon practice, though
> > the macro itself can be used by anyone.
> >
> > Signed-off-by: Darrick J. Wong <djwong at us.ibm.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 fba141d..fb02266 100644
> > --- a/include/linux/kernel.h
> > +++ b/include/linux/kernel.h
> > @@ -48,6 +48,12 @@ extern const char linux_proc_banner[];
> > #define FIELD_SIZEOF(t, f) (sizeof(((t*)0)->f))
> > #define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
> > #define roundup(x, y) ((((x) + ((y) - 1)) / (y)) * (y))
> > +#define DIV_ROUND_CLOSEST(x, divisor)( \
> > +{ \
> > + typeof(divisor) __divisor = divisor; \
> > + (((x) + ((__divisor) / 2)) / (__divisor)); \
> > +} \
> > +)
> >
> > #define _RET_IP_ (unsigned long)__builtin_return_address(0)
> > #define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
> >
>
> I don't get why you implement this as a macro rather than an inline
> function? A function would look much better.
The idea is that DIV_ROUND_CLOSEST() can be used with arguments of any
size (char, short, ... long long) and will do all the suitable
promotion and will return a type of the appropriate width and
signedness.
It's not particularly pretty and can hide traps and pitfalls, but the
other way is tricky as well - it'd need a family of functions and
there's a risk that programmers will choose the wrong one.
