| Message ID | 20150331211826.1133.19645.stgit@ahduyck-vm-fedora22 |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Alexander Duyck <alexander.h.duyck@redhat.com> Date: Tue, 31 Mar 2015 14:19:10 -0700 > 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> This looks correct to me, applied, thanks! -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/jhash.h b/include/linux/jhash.h index 47cb09edec1a..348c6f47e4cc 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 */
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> --- include/linux/jhash.h | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html