Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 12 Dec 2011 15:50:11 -0800 | Subject | Re: [PATCH] include/log2.h: Fix rounddown_pow_of_two(1) |
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On Mon, Dec 12, 2011 at 10:02 AM, Dmitry Torokhov <dtor@vmware.com> wrote: > From: Andrei Warkentin <andreiw@vmware.com> > > 1 is a power of two, therefore rounddown_pow_of_two(1) should return 1. > It does in case the argument is a variable but in case it's a constant > it behaves incorrectly and returns 0. Probably nobody ever did it so > this was never noticed, however drivers/net/vmxnet3 with latest GCC does > and breaks on unicpu systems. > > This is similar to Rolf's patch to roundup_pow_of_two(1).
Umm. I already applied this patch, but then I started looking at it more, and asked myself:
- Why is that "n == 1" test there AT ALL?
Afaik, that whole test is just plain stupid. It seems to have been copied from the "roundup()" case (where it exists due to the "-1/+1" hackery that breaks ilog2()) without any thought about the actual math of the function at all.
I think the *real* fix is to just remove that incorrect line, no?
It's a bit sad that we apparently have several reviewers for this trivial patch, and nobody reacted to the math just not making any sense.
Linus
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