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author | Stanislaw Gruszka <sgruszka@redhat.com> | 2019-03-07 16:28:18 -0800 |
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committer | Ben Hutchings <ben@decadent.org.uk> | 2019-07-09 22:04:14 +0100 |
commit | c70d1929aa130f2a9fa00dd2ca6ac532bcb599e9 (patch) | |
tree | e6f3f1d9dc91e3b96a377de8dc8387ef4d10e6d7 | |
parent | d7ee7a3fcf72cfea7852d101e0223335ff7e9759 (diff) | |
download | linux-stable-c70d1929aa130f2a9fa00dd2ca6ac532bcb599e9.tar.gz linux-stable-c70d1929aa130f2a9fa00dd2ca6ac532bcb599e9.tar.bz2 linux-stable-c70d1929aa130f2a9fa00dd2ca6ac532bcb599e9.zip |
lib/div64.c: off by one in shift
commit cdc94a37493135e355dfc0b0e086d84e3eadb50d upstream.
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: Ben Hutchings <ben@decadent.org.uk>
-rw-r--r-- | lib/div64.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/lib/div64.c b/lib/div64.c index 4382ad77777e..ce76dc3d674e 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -100,7 +100,7 @@ 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) @@ -138,7 +138,7 @@ 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) |