Re: abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode
From: Michal Januszewski <hidden>
Date: 2010-11-19 22:28:33
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On Fri, Nov 19, 2010 at 02:07:21PM -0800, Andrew Morton wrote:
On Thu, 18 Nov 2010 07:40:19 +0100 Geert Uytterhoeven [off-list ref] wrote:
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'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.
quoted hunk ↗ jump to hunk
How does this look? [..] Reported-by: Michal Januszewski <redacted> 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&m8033094822201&w=2) but it then failed to get any traction. At any rate, I like your version better as it seems more readable. Michal