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
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This archive was generated by hypermail 2b29 : Tue Jul 15 2003 - 22:00:59 EST