Messages in this thread | | | Date | Tue, 15 Jul 2003 18:43:37 +0100 | From | Jamie Lokier <> | Subject | Re: Interrupt doesn't make it to the 8259 on a ASUS P4PE mobo |
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Brian Gerst wrote: > >>>dmatimer.expires = jiffies + 0.5*HZ; > >> > >>That's a serious bug. You cannot use floating point in the kernel. > >>It will corrupt the FP state of the user process. > > > >HZ on the INTEL platform is 100, so this should simply add 50 to the > >current > >value of jiffies. Besides, assigning the value to the unsigned int field > >(expires) will truncate it to an integer anyway. > > Use HZ/2 instead. GCC doesn't optimize floating point constants to the > same degree it does integers, because it doesn't know what mode > (rounding, precision) the FPU is in.
Optimising this to an integer add of 50 would be incorrect anyway. Think about jiffies == 0xfffffffe.
The first statement is equivalent to:
dmatimer.expires = (unsigned long) ((double) + 50)
and would set dmatimer.expires to 0xffffffff.
Whereas the HZ/2 form is correct!
Have a nice day, -- Jamie - 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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