Messages in this thread | | | Date | Sat, 21 Dec 2002 08:46:12 -0800 | From | george anzinger <> | Subject | Re: [PATCH] joydev: fix HZ->millisecond transformation |
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Vojtech Pavlik wrote: > > On Fri, Dec 20, 2002 at 10:16:27AM -0800, george anzinger wrote: > > Vojtech Pavlik wrote: > > > > > > On Fri, Dec 20, 2002 at 09:24:58AM -0800, george anzinger wrote: > > > > Vojtech Pavlik wrote: > > > > > > > > > > On Fri, Dec 20, 2002 at 02:41:50AM -0800, george anzinger wrote: > > > > > > Bjorn Helgaas wrote: > > > > > > > > > > > > > > * fix a problem with HZ->millisecond transformation on > > > > > > > non-x86 archs (from 2.5 change by vojtech@suse.cz) > > > > > > > > > > > > > > Applies to 2.4.20. > > > > > > > > > > > > > > diff -Nru a/drivers/input/joydev.c b/drivers/input/joydev.c > > > > > > > --- a/drivers/input/joydev.c Mon Dec 16 12:16:32 2002 > > > > > > > +++ b/drivers/input/joydev.c Mon Dec 16 12:16:32 2002 > > > > > > > @@ -50,6 +50,8 @@ > > > > > > > #define JOYDEV_MINORS 32 > > > > > > > #define JOYDEV_BUFFER_SIZE 64 > > > > > > > > > > > > > > +#define MSECS(t) (1000 * ((t) / HZ) + 1000 * ((t) % HZ) / HZ) > > > > > > Uh... > > > > > > ^^^^^^^^^^^^^^^^ > > > > > > by definition this is zero, is it not? > > > > > > > > > > No, both parts of the equaition can be nonzero. > > > > > > > > I don't think so. s%HZ has to be less than HZ. Then > > > > dividing that by HZ should result in zero. Where is my > > > > thinking flawed? > > > > > > You first multiply it by 1000. > > > > But then it should read: (1000 * (t)) % HZ) / HZ > > The expression is evaluated from left to right. No need for parentheses > here. > > > But this is still zero. There is no way that ((X % HZ) / > > HZ) is other than zero, me thinks. > > Example: > > HZ = 100 > t = 70 > > 1000 * (t % HZ) / HZ = 1000 * 70 / 100 = 700 != 0 > > Anyway (x % HZ) / HZ must be zero, but that's something different.
OK, I miss read the "("s. :( > > > > > > Though it might be easier to say (1000 * t) / HZ, now that I think about > > > > > it. > > > > > > > > That overflows... As does the other if HZ is less than 1000.... > > > > > > You're right, t can be all 32 bits. > > > > What, exactly, is this code trying to do? It looks like the > > number is being passed to user space... > > It's trying to convert jiffies to microseconds from computer start (or > any other arbitrary point in time), thus making the value independent of > HZ. > This is possible, but in general it can not be kept in one 32-bit word. I don't know what it is used for or if the format can be changed, but the struct timeval comes to mind. -- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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