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authorStanislaw Gruszka <sgruszka@redhat.com>2019-03-07 16:28:18 -0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-04-20 09:17:04 +0200
commit78154e3198885b037aa30bbf9539747c2692656a (patch)
treef74a08b97eb8693f9d7c98e401859d703cdc4fbe
parentf0f1c97f38b890c5eea33dfd60fb2d12657ba0ef (diff)
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lib/div64.c: off by one in shift
[ Upstream commit cdc94a37493135e355dfc0b0e086d84e3eadb50d ] fls counts bits starting from 1 to 32 (returns 0 for zero argument). If we add 1 we shift right one bit more and loose precision from divisor, what cause function incorect results with some numbers. Corrected code was tested in user-space, see bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=202391 Link: http://lkml.kernel.org/r/1548686944-11891-1-git-send-email-sgruszka@redhat.com Fixes: 658716d19f8f ("div64_u64(): improve precision on 32bit platforms") Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com> Reported-by: Siarhei Volkau <lis8215@gmail.com> Tested-by: Siarhei Volkau <lis8215@gmail.com> Acked-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r--lib/div64.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/div64.c b/lib/div64.c
index 01c8602bb6ff..ee146bb4c558 100644
--- a/lib/div64.c
+++ b/lib/div64.c
@@ -109,7 +109,7 @@ u64 div64_u64_rem(u64 dividend, u64 divisor, u64 *remainder)
quot = div_u64_rem(dividend, divisor, &rem32);
*remainder = rem32;
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)
@@ -147,7 +147,7 @@ u64 div64_u64(u64 dividend, u64 divisor)
if (high == 0) {
quot = div_u64(dividend, divisor);
} else {
- int n = 1 + fls(high);
+ int n = fls(high);
quot = div_u64(dividend >> n, divisor >> n);
if (quot != 0)