Hi Linus,
> >
> > In short: It is wrong to do
> >
> > if (jiffies <= start+HZ)
> >
> > and it is _right_ to do
> >
> > if (jiffies - start <= HZ)
>
> Actually this last part is wrong, isn't it ? jiffies <= start + HZ is
also
> a correct way to do it, since start+HZ will overflow to the current value
> of jiffies when HZ time elapses. So the above two statements are
IDENTICAL.
>
> No.
>
> Try it out with a few examples. You'll see.
>
> Linus
I am sorry, but I still don't see the difference. I wrote a small program
with different
cases, but the values still come same irrespective of the input arguments
to the
checks. Could you tell under what conditions the checks wuold fail ? The
2's
complement works the same for addition and subtraction. I have included
the
test program below.
Thanks,
- KK
---------------------------------------------------------------------------------------------
/*
if (jiffies <= start+HZ)
if (jiffies - start <= HZ)
*/
#define HZ 100
main()
{
unsigned long start, jiffies;
/* Case 1 */
start = ((unsigned long) -1);
jiffies = start + HZ;
if (jiffies <= start + HZ) {
printf("Less Case 1\n");
}
if (jiffies - start <= HZ) {
printf("Less Case 2\n");
}
/* Case 2 */
start = ((unsigned long) -10);
jiffies = start + HZ + 1;
if (jiffies <= start + HZ) {
printf("Less Case 3\n");
}
if (jiffies - start <= HZ) {
printf("Less Case 4\n");
}
/* Case 3 */
start = ((unsigned long) -10);
jiffies = start + HZ - 1;
if (jiffies <= start + HZ) {
printf("Less Case 5\n");
}
if (jiffies - start <= HZ) {
printf("Less Case 6\n");
}
}
-
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/
This archive was generated by hypermail 2b29 : Thu Nov 15 2001 - 21:00:18 EST