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Linus Torvalds 13c07b0286 linux/log2.h: Fix rounddown_pow_of_two(1) 
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 1a06a52ee1: "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>
2011-12-12 22:06:55 -08:00
..
acpi Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux 2011-11-07 10:13:52 -08:00
asm-generic asm-generic/unistd.h: support new process_vm_{readv,write} syscalls 2011-12-03 15:31:48 -05:00
crypto
drm drm/radeon/kms: add some new pci ids 2011-12-01 16:34:15 +00:00
keys
linux linux/log2.h: Fix rounddown_pow_of_two(1) 2011-12-12 22:06:55 -08:00
math-emu
media Merge branch 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux 2011-11-06 19:44:47 -08:00
misc
mtd
net sch_red: fix red_calc_qavg_from_idle_time 2011-11-30 23:27:22 -05:00
pcmcia
rdma
rxrpc
scsi
sound Merge branch 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux 2011-11-06 19:44:47 -08:00
target target: remove the unused se_dev_list 2011-12-06 06:00:57 +00:00
trace Merge branch 'modsplit-Oct31_2011' of git://git.kernel.org/pub/scm/linux/kernel/git/paulg/linux 2011-11-06 19:44:47 -08:00
video ARM: OMAP: HWMOD: Unify DSS resets for OMAPs 2011-11-08 03:16:13 -07:00
xen xen: Remove hanging references to CONFIG_XEN_PLATFORM_PCI 2011-11-16 12:13:42 -05:00
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