Author: Tom Likens

Date: 10:00:05 09/02/03

This is a general query about an issue I've run into and I'm wondering if anyone else has dealt with it or if I'm just off base. Essentially, the issue is this- recently I started playing around with my hash table's random numbers to see if I could improve them. Currently, for the main table I have a Hamming distance of 24 for roughly 800 random 64-bit values. This is where my inquiry comes in, I use the lower N bits of my hash key as an index into the table. I'm wondering, even though the overall Hamming distance is 24 shouldn't I be concerned about the Hamming distance of the lower N bits? If these bits are alike, even though the overal value is reasonable don't it increase the probablity of hash collisions considerably? Of course, I won't get a false match since I still use all 64-bits of the key to indicate if the hash entry is valid, but it's time wasted performing multiple probes into the table. I'm also guessing that this could be more of an issue for the repetition hash table, since it is quite a bit smaller than the main table. Currently, I don't do multiple probes into this table and I've never seen an issue. Still, I'm starting to wonder if there is a problem lurking below the surface that I may have missed. Anyway, I'm probably missing something obvious here. I intend to run a number of experiments this evening, but I was curious if anyone else has given this much thought. regards, --tom

- Re: Hamming distance and lower hash table indexing
**Tony Werten***23:36:33 09/02/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***07:52:35 09/03/03*- Re: Hamming distance and lower hash table indexing
**Frank Phillips***10:28:20 09/03/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***10:43:13 09/03/03*- Re: Hamming distance and lower hash table indexing
**Dieter Buerssner***13:28:14 09/03/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***19:59:17 09/03/03*- Re: Hamming distance and lower hash table indexing
**Dieter Buerssner***10:57:07 09/04/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***12:11:57 09/04/03*

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing
- Re: Hamming distance and lower hash table indexing
**Frank Phillips***11:09:18 09/03/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***11:33:18 09/03/03*

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing
- Re: Hamming distance and lower hash table indexing
**Anthony Cozzie***08:10:29 09/03/03*- Re: Hamming distance and lower hash table indexing
**Tom Likens***10:29:45 09/03/03*- Re: Hamming distance and lower hash table indexing
**Anthony Cozzie***10:43:26 09/03/03*

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing

- Re: Hamming distance and lower hash table indexing

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