Re: [git pull] timer fix

[Linus Torvalds]

On Wed, 4 Feb 2009, Linus Torvalds wrote:
> 
> Either cast the result of the subtract to "s32" (or "int", whatever), or 
> cast _both_ of them to (s32) so that the subtract is done in a signed 
> type, and then the expansion to (long) will still be right - but 
> unnecessary - in the sign.

Btw, doing it with a nice helper macro or function is also perhaps a good 
idea, at least if these "compare hpet values" things happen more than 
once. 

Look at "time_after()" in <linux/jiffies.h> to see how to do these kinds 
of "comparisons of things that may overflow" really carefully. You 
absolutely need to do the compare in a size that is no larger than the 
size of the actual values (and in the case of HPET, it's 32-bit, at least 
the way we do things now - I guess HPET's _could_ be 64-bit, but we don't 
read more than 32 bits or whatever).

So <linux/jiffies.h> does the cast to "(long)", but it does so because the 
incoming values really have type "unsigned long" and are valid in all 
bits.

			Linus
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