Messages in this thread | | | Subject | Re: [PATCH] net/ipv4/*, net/core/neighbour.c jiffies cleanup | From | "Krishna Kumar" <> | Date | Thu, 8 Nov 2001 08:55:51 -0800 |
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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"); } }
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