Messages in this thread | | | Date | Wed, 21 Feb 2001 23:32:04 +0100 | From | Martin Mares <> | Subject | Re: [rfc] Near-constant time directory index for Ext2 |
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Hello!
> Not true. The rehashing is O(n) and it has to be performed O(log n) > times during insertion. Therefore, insertion is O(log n).
Rehashing is O(n), but the "n" is the _current_ number of items, not the maximum one after all the insertions.
Let's assume you start with a single-entry hash table. You rehash for the first time after inserting the first item (giving hash table of size 2), then after the second item (=> size 4), then after the fourth item (=> size 8) and so on. I.e., when you insert n items, the total cost of rehashing summed over all the insertions is at most 1 + 2 + 4 + 8 + 16 + ... + 2^k (where k=floor(log2(n))) <= 2^k+1 = O(n). That is O(1) operations per item inserted.
Have a nice fortnight -- Martin `MJ' Mares <mj@ucw.cz> <mj@suse.cz> http://atrey.karlin.mff.cuni.cz/~mj/ MIPS: Meaningless Indicator of Processor Speed. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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