[PATCH 3.4 027/146] jhash: Update jhash_[321]words functions to use correct initval

lizf
2015-09-15T09:06:50Z

From: Alexander Duyck <alexander.h.duyck@redhat.com>

3.4.109-rc1 review patch. If anyone has any objections, please let me know.

------------------

commit 2e7056c433216f406b90a003aa0ba42e19d3bdcf upstream.

Looking over the implementation for jhash2 and comparing it to jhash_3words
I realized that the two hashes were in fact very different. Doing a bit of
digging led me to "The new jhash implementation" in which lookup2 was
supposed to have been replaced with lookup3.

In reviewing the patch I noticed that jhash2 had originally initialized a
and b to JHASH_GOLDENRATIO and c to initval, but after the patch a, b, and
c were initialized to initval + (length << 2) + JHASH_INITVAL. However the
changes in jhash_3words simply replaced the initialization of a and b with
JHASH_INITVAL.

This change corrects what I believe was an oversight so that a, b, and c in
jhash_3words all have the same value added consisting of initval + (length
<< 2) + JHASH_INITVAL so that jhash2 and jhash_3words will now produce the
same hash result given the same inputs.

Fixes: 60d509c823cca ("The new jhash implementation")
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
include/linux/jhash.h | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/jhash.h b/include/linux/jhash.h
index 47cb09e..348c6f4 100644
--- a/include/linux/jhash.h
+++ b/include/linux/jhash.h
@@ -145,11 +145,11 @@ static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
}

-/* jhash_3words - hash exactly 3, 2 or 1 word(s) */
-static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
+/* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */
+static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval)
{
- a += JHASH_INITVAL;
- b += JHASH_INITVAL;
+ a += initval;
+ b += initval;
c += initval;

__jhash_final(a, b, c);
@@ -157,14 +157,19 @@ static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
return c;
}

+static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval)
+{
+ return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2));
+}
+
static inline u32 jhash_2words(u32 a, u32 b, u32 initval)
{
- return jhash_3words(a, b, 0, initval);
+ return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2));
}

static inline u32 jhash_1word(u32 a, u32 initval)
{
- return jhash_3words(a, 0, 0, initval);
+ return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2));
}

#endif /* _LINUX_JHASH_H */
--
1.9.1