Messages in this thread | | | Subject | Re: [PATCH] net/ipv4/*, net/core/neighbour.c jiffies cleanup | From | "Krishna Kumar" <> | Date | Wed, 7 Nov 2001 19:07:47 -0800 |
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> Unsigned arithmetic is fine. The _correct_ way to test whether something > is in within > > [ start , start+HZ ] > > is to do > > if (jiffies - start <= HZ) > > try it. The C language guarantees that unsigned arithmetic works in a > "modulo power of two" fashion, which means that it _is_ ok to do > arithmetic on unsigned longs, and jiffy wrapping does not matter. No need > to cast to "signed" or anything else. > > 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. I agree with the rest of the statements, and especially that you don't need to worry about wrapping using unsigned numbers.
Regards,
- KK
> (as long as "start" is "unsigned long" like jiffies). > > Linus
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