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.
Unified · Split
| @@ -145,11 +145,11 @@ static inline u32 jhash2(const u32 *k, u32 length, u32 initval) · 144 unmodified lines | ||
| 145 | 145 | } |
| 146 | 146 | |
| 147 | 147 | |
| 148 | −/* jhash_3words - hash exactly 3, 2 or 1 word(s) */ | |
| 149 | −static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) | |
| 148 | +/* __jhash_nwords - hash exactly 3, 2 or 1 word(s) */ | |
| 149 | +static inline u32 __jhash_nwords(u32 a, u32 b, u32 c, u32 initval) | |
| 150 | 150 | { |
| 151 | − a += JHASH_INITVAL; | |
| 152 | − b += JHASH_INITVAL; | |
| 151 | + a += initval; | |
| 152 | + b += initval; | |
| 153 | 153 | c += initval; |
| 154 | 154 | |
| 155 | 155 | __jhash_final(a, b, c); |
| @@ -157,14 +157,19 @@ static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) · 1 unmodified line | ||
| 157 | 157 | return c; |
| 158 | 158 | } |
| 159 | 159 | |
| 160 | +static inline u32 jhash_3words(u32 a, u32 b, u32 c, u32 initval) | |
| 161 | +{ | |
| 162 | + return __jhash_nwords(a, b, c, initval + JHASH_INITVAL + (3 << 2)); | |
| 163 | +} | |
| 164 | + | |
| 160 | 165 | static inline u32 jhash_2words(u32 a, u32 b, u32 initval) |
| 161 | 166 | { |
| 162 | − return jhash_3words(a, b, 0, initval); | |
| 167 | + return __jhash_nwords(a, b, 0, initval + JHASH_INITVAL + (2 << 2)); | |
| 163 | 168 | } |
| 164 | 169 | |
| 165 | 170 | static inline u32 jhash_1word(u32 a, u32 initval) |
| 166 | 171 | { |
| 167 | − return jhash_3words(a, 0, 0, initval); | |
| 172 | + return __jhash_nwords(a, 0, 0, initval + JHASH_INITVAL + (1 << 2)); | |
| 168 | 173 | } |
| 169 | 174 | |
| 170 | 175 | #endif /* _LINUX_JHASH_H */ |