54 lines
1.8 KiB
C
54 lines
1.8 KiB
C
/* RCS $Id: hash.c,v 1.2 2006-09-25 09:39:55 vg Exp $
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--
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-- SYNOPSIS
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-- Hashing function for hash tables.
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--
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-- DESCRIPTION
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-- Hash an identifier. The hashing function works by computing the sum
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-- of each char and the previous hash value multiplied by 129. Finally the
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-- length of the identifier is added in. This way the hash depends on the
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-- chars as well as the length, and appears to be sufficiently unique,
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-- and is FAST to COMPUTE, unlike the previous hash function...
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--
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-- AUTHOR
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-- Dennis Vadura, dvadura@dmake.wticorp.com
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--
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-- WWW
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-- http://dmake.wticorp.com/
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--
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-- COPYRIGHT
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-- Copyright (c) 1996,1997 by WTI Corp. All rights reserved.
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--
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-- This program is NOT free software; you can redistribute it and/or
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-- modify it under the terms of the Software License Agreement Provided
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-- in the file <distribution-root>/readme/license.txt.
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--
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-- LOG
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-- Use cvs log to obtain detailed change logs.
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*/
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#include "extern.h"
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PUBLIC uint16
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Hash( id, phv )/*
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=================
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This function computes the identifier's hash value and returns the hash
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value modulo the key size as well as the full hash value. The reason
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for returning both is so that hash table searches can be sped up. You
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compare hash keys instead and compare strings only for those whose 32-bit
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hash keys match. (not many) */
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char *id; /* value */
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uint32 *phv; /* key */
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{
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register char *p = id;
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register uint32 hash = (uint32) 0;
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while( *p ) hash = (hash << 7) + hash + (uint32) (*p++);
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*phv = hash = hash + (uint32) (p-id);
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/* return an index (for Macs[]) where all keys with the same remainder
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* after integer division with HASH_TABLE_SIZE are stored. */
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return( (uint16) (hash % HASH_TABLE_SIZE) );
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}
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