Messages in this thread Patch in this message | | | Date | Fri, 19 Nov 2010 15:04:11 -0800 | From | Andrew Morton <> | Subject | Re: abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) |
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On Fri, 19 Nov 2010 23:28:23 +0100 Michal Januszewski <michalj@gmail.com> wrote:
> On Fri, Nov 19, 2010 at 02:07:21PM -0800, Andrew Morton wrote: > > On Thu, 18 Nov 2010 07:40:19 +0100 > > Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > > > > 'c' will end up with a value of 0xffffffff instead of the expected 0x1. > > > > > > This happens on 64-bit only, right? > > Absolutely, I should have mentioned it in the patch description. > > > How does this look? > > > > [..] > > > > Reported-by: Michal Januszewski <michalj@gmail.com> > > Cc: Rolf Eike Beer <eike-kernel@sf-tec.de > > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > > --- > > > > include/linux/kernel.h | 13 ++++++++++--- > > 1 file changed, 10 insertions(+), 3 deletions(-) > > > > diff -puN include/linux/kernel.h~include-linux-kernelh-abs-fix-handling-of-32-bit-unsigneds-on-64-bit include/linux/kernel.h > > --- a/include/linux/kernel.h~include-linux-kernelh-abs-fix-handling-of-32-bit-unsigneds-on-64-bit > > +++ a/include/linux/kernel.h > > @@ -143,9 +143,16 @@ extern int _cond_resched(void); > > > > #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0) > > > > -#define abs(x) ({ \ > > - long __x = (x); \ > > - (__x < 0) ? -__x : __x; \ > > +#define abs(x) ({ \ > > + long ret; \ > > + if (sizeof(x) == sizeof(long)) { \ > > + long __x = (x); \ > > + ret = (__x < 0) ? -__x : __x; \ > > + } else { \ > > + int __x = (x); \ > > + ret = (__x < 0) ? -__x : __x; \ > > + } \ > > + ret; \ > > }) > > > > #define abs64(x) ({ \ > > _ > > Looks good to me. I posted essentially the same thing some 3 months ago > (http://marc.info/?l=linux-kernel&m=128033094822201&w=2) but it then > failed to get any traction. At any rate, I like your version better as > it seems more readable. >
I spose we should document it. Does this look complete and accurate?
--- a/include/linux/kernel.h~include-linux-kernelh-abs-fix-handling-of-32-bit-unsigneds-on-64-bit-fix +++ a/include/linux/kernel.h @@ -143,6 +143,13 @@ extern int _cond_resched(void); #define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0) +/* + * abs() handles unsigned and signed longs, ints, shorts and chars. For long + * types it returns a signed long. For int, short and char types it returns a + * signed int. + * abs() should not be used for 64-bit types (s64, u64, long long) - use abs64() + * for those. + */ #define abs(x) ({ \ long ret; \ if (sizeof(x) == sizeof(long)) { \ _
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