Commit 2e7056c4 authored Mar 31, 2015 by Alexander Duyck Committed by David S. Miller Apr 03, 2015

jhash: Update jhash_[321]words functions to use correct initval



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: 60d509c8 ("The new jhash implementation")
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 5c5e0ad3

include/linux/jhash.h

+11 −6

Original line number	Diff line number	Diff line
		@@ -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 */

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