On 16/03/2009, at 7:37 PM, Jean-Daniel Dupas wrote:
That's why a good hash table uses primary numbers as table size
This only helps if the hash function distributes more or less randomly. If your hash function turned out to hit multiples of the hash table size, prime or not, you'd end up colliding every time.
Trivial and contrived example - hash table size = 13 (prime), hash function of a string = first char of string % 26 (for a..z, say).
OK, so that's a seriously dysfunctional hash function, but it's not unheard of for hash functions to have a periodicity, and if that periodicity is non-prime in itself, then it will have prime factors that *could* equal the table size. With integer indexes as the "hash", this could be fairly likely.
--Graham _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
