https://github.com/torvalds/linux
Revision 13c07b0286d340275f2d97adf085cecda37ede37 authored by Linus Torvalds on 13 December 2011, 06:06:55 UTC, committed by Linus Torvalds on 13 December 2011, 06:06:55 UTC
Exactly like roundup_pow_of_two(1), the rounddown version was buggy for the case of a compile-time constant '1' argument. Probably because it originated from the same code, sharing history with the roundup version from before the bugfix (for that one, see commit 1a06a52ee1b0: "Fix roundup_pow_of_two(1)"). However, unlike the roundup version, the fix for rounddown is to just remove the broken special case entirely. It's simply not needed - the generic code 1UL << ilog2(n) does the right thing for the constant '1' argment too. The only reason roundup needed that special case was because rounding up does so by subtracting one from the argument (and then adding one to the result) causing the obvious problems with "ilog2(0)". But rounddown doesn't do any of that, since ilog2() naturally truncates (ie "rounds down") to the right rounded down value. And without the ilog2(0) case, there's no reason for the special case that had the wrong value. tl;dr: rounddown_pow_of_two(1) should be 1, not 0. Acked-by: Dmitry Torokhov <dtor@vmware.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Tip revision: 13c07b0286d340275f2d97adf085cecda37ede37 authored by Linus Torvalds on 13 December 2011, 06:06:55 UTC
linux/log2.h: Fix rounddown_pow_of_two(1)
linux/log2.h: Fix rounddown_pow_of_two(1)
Tip revision: 13c07b0
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