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Date: Wed, 4 Feb 2009 14:16:23 -0800 (PST) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Ingo Molnar <mingo@...e.hu> cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [git pull] timer fix 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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