I have used the technique of adding byte values for a hash count in two shops over two decades to cut the length of a threaded list. Both times I used mod256 to good effect.
The first time the string was an eight character variable name, the second time a set of strings over 64 bytes long. Both could contain spaces. In the first case the set was in the low thousands and short/long ratio was less than 3/1. In the second case, worst case set was above 1 million and the short long ratio was less than 1.5/1. In this case, the performance hit is low enough (and probably the systems fast enough) that it does not pay to go mod512. A million pages is still a technology limit for the kind of reports being indexed. One thing that helped in both cases was allocating control blocks pointed to by the hash tables in sets of pages to improve locality of reference. IBM Mainframe Discussion List <IBM-MAIN@bama.ua.edu> wrote on 07/27/2010 03:18:49 PM: > From: Binyamin Dissen <bdis...@dissensoftware.com> > Subject: Hashing algorythm for text strings without embedded blanks > > Is there a preferred hashing algorithm for such strings? The strings will be > fixed length with trailing blanks. > > I was thinking of simply doing a MOD64 (or higher) of the sum of thenon-blank > part of the string by words, but as this is text with a limited character set, > would this lead to excessive alias chains? Has research been done in this > area? There will mostly be search activity but also add activity. ----------------------------------------- The information contained in this communication (including any attachments hereto) is confidential and is intended solely for the personal and confidential use of the individual or entity to whom it is addressed. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that you have received this communication in error and that any review, dissemination, copying, or unauthorized use of this information, or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this communication in error, please notify us immediately by e-mail, and delete the original message. Thank you ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@bama.ua.edu with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
