diff options
Diffstat (limited to 'mysys/hash.c')
| -rw-r--r-- | mysys/hash.c | 45 |
1 files changed, 45 insertions, 0 deletions
diff --git a/mysys/hash.c b/mysys/hash.c index 9c6497c7717..b366554272a 100644 --- a/mysys/hash.c +++ b/mysys/hash.c @@ -108,6 +108,8 @@ static uint hash_rec_mask(HASH *hash,HASH_LINK *pos,uint buffmax, return hash_mask((*hash->calc_hashnr)(key,length),buffmax,maxlength); } +#ifndef NEW_HASH_FUNCTION + /* Calc hashvalue for a key */ static uint calc_hashnr(const byte *key,uint length) @@ -134,6 +136,49 @@ static uint calc_hashnr_caseup(const byte *key,uint length) return((uint) nr); } +#else + +/* + * Fowler/Noll/Vo hash + * + * The basis of the hash algorithm was taken from an idea sent by email to the + * IEEE Posix P1003.2 mailing list from Phong Vo (kpv@research.att.com) and + * Glenn Fowler (gsf@research.att.com). Landon Curt Noll (chongo@toad.com) + * later improved on their algorithm. + * + * The magic is in the interesting relationship between the special prime + * 16777619 (2^24 + 403) and 2^32 and 2^8. + * + * This hash produces the fewest collisions of any function that we've seen so + * far, and works well on both numbers and strings. + */ + +uint calc_hashnr(const byte *key, uint len) +{ + const byte *end=key+len; + uint hash; + for (hash = 0; key < end; key++) + { + hash *= 16777619; + hash ^= (uint) *(uchar*) key; + } + return (hash); +} + +uint calc_hashnr_caseup(const byte *key, uint len) +{ + const byte *end=key+len; + uint hash; + for (hash = 0; key < end; key++) + { + hash *= 16777619; + hash ^= (uint) (uchar) toupper(*key); + } + return (hash); +} + +#endif + static inline uint rec_hashnr(HASH *hash,const byte *record) { |