From: Geert Uytterhoeven <geert@linux-m68k.org> To: Andrew Morton <akpm@linux-foundation.org> Cc: michalj@gmail.com, Rolf Eike Beer <eike-kernel@sf-tec.de>, linux-kernel@vger.kernel.org, Linux Fbdev development list <linux-fbdev@vger.kernel.org> Subject: Re: abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Date: Sat, 20 Nov 2010 09:56:24 +0100 [thread overview] Message-ID: <AANLkTinneJ+PcnZ9zFVjYUeA+-9MQ96-67kqvO=gS7zW@mail.gmail.com> (raw) In-Reply-To: <20101119151949.b7e514f7.akpm@linux-foundation.org> On Sat, Nov 20, 2010 at 00:19, Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 19 Nov 2010 15:04:11 -0800 > Andrew Morton <akpm@linux-foundation.org> wrote: > >> > 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)) { \ > > Well that was a load of bollocks. 2nd attempt: Yeah, I was just gonna complain "but long _is_ 64-bit on 64-bit platforms"... > --- 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 +143,12 @@ 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 all > + * input types abs() returns a signed long. > + * 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)) { \ After some second thinking, I think this is OK... In the first patch: > of similarity between video modes. The arguments of abs() are sometimes > unsigned numbers. This worked fine until commit a49c59c0 ("Make sure the The "sometimes" is when the parameter is the difference of 2 numbers, which is a highly likely use case. Unlike most people's intuitive mathematical feelings, a difference is always unsigned in C (that was incorrect in the comment of Michal's first version). So I think it's worth mentioning that explicitly. ... and please llet me do the third thinking during the rest of the day ;-) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
WARNING: multiple messages have this Message-ID (diff)
From: Geert Uytterhoeven <geert@linux-m68k.org> To: Andrew Morton <akpm@linux-foundation.org> Cc: michalj@gmail.com, Rolf Eike Beer <eike-kernel@sf-tec.de>, linux-kernel@vger.kernel.org, Linux Fbdev development list <linux-fbdev@vger.kernel.org> Subject: Re: abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Date: Sat, 20 Nov 2010 08:56:24 +0000 [thread overview] Message-ID: <AANLkTinneJ+PcnZ9zFVjYUeA+-9MQ96-67kqvO=gS7zW@mail.gmail.com> (raw) In-Reply-To: <20101119151949.b7e514f7.akpm@linux-foundation.org> On Sat, Nov 20, 2010 at 00:19, Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 19 Nov 2010 15:04:11 -0800 > Andrew Morton <akpm@linux-foundation.org> wrote: > >> > Looks good to me. I posted essentially the same thing some 3 months ago >> > (http://marc.info/?l=linux-kernel&m\x128033094822201&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)) { \ > > Well that was a load of bollocks. 2nd attempt: Yeah, I was just gonna complain "but long _is_ 64-bit on 64-bit platforms"... > --- 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 +143,12 @@ 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 all > + * input types abs() returns a signed long. > + * 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)) { \ After some second thinking, I think this is OK... In the first patch: > of similarity between video modes. The arguments of abs() are sometimes > unsigned numbers. This worked fine until commit a49c59c0 ("Make sure the The "sometimes" is when the parameter is the difference of 2 numbers, which is a highly likely use case. Unlike most people's intuitive mathematical feelings, a difference is always unsigned in C (that was incorrect in the comment of Michal's first version). So I think it's worth mentioning that explicitly. ... and please llet me do the third thinking during the rest of the day ;-) Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
next prev parent reply other threads:[~2010-11-20 8:56 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2010-11-18 6:40 abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Geert Uytterhoeven 2010-11-18 6:40 ` Geert Uytterhoeven 2010-11-19 22:07 ` Andrew Morton 2010-11-19 22:07 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode Andrew Morton 2010-11-19 22:28 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Michal Januszewski 2010-11-19 22:28 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode Michal Januszewski 2010-11-19 23:04 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Andrew Morton 2010-11-19 23:04 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode Andrew Morton 2010-11-19 23:19 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Andrew Morton 2010-11-19 23:19 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode Andrew Morton 2010-11-20 8:56 ` Geert Uytterhoeven [this message] 2010-11-20 8:56 ` abs() vs. abs64() (was: Re: [PATCH] fbdev: fix nearest mode search) Geert Uytterhoeven
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