1/* hash.c - The gdbm hash function. */ 2 3/* This file is part of GDBM, the GNU data base manager, by Philip A. Nelson. 4 Copyright (C) 1990, 1991, 1993 Free Software Foundation, Inc. 5 6 GDBM is free software; you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 2, or (at your option) 9 any later version. 10 11 GDBM is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with GDBM; see the file COPYING. If not, write to 18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. 19 20 You may contact the author by: 21 e-mail: phil@cs.wwu.edu 22 us-mail: Philip A. Nelson 23 Computer Science Department 24 Western Washington University 25 Bellingham, WA 98226 26 27*************************************************************************/ 28 29 30/* include system configuration before all else. */ 31#include "autoconf.h" 32 33#include "gdbmdefs.h" 34 35 36/* This hash function computes a 31 bit value. The value is used to index 37 the hash directory using the top n bits. It is also used in a hash bucket 38 to find the home position of the element by taking the value modulo the 39 bucket hash table size. */ 40 41int 42_gdbm_hash (key) 43 datum key; 44{ 45 unsigned int value; /* Used to compute the hash value. */ 46 int index; /* Used to cycle through random values. */ 47 48 49 /* Set the initial value from key. */ 50 value = 0x238F13AF * key.dsize; 51 for (index = 0; index < key.dsize; index++) 52 value = (value + (key.dptr[index] << (index*5 % 24))) & 0x7FFFFFFF; 53 54 value = (1103515243 * value + 12345) & 0x7FFFFFFF; 55 56 /* Return the value. */ 57 return((int) value); 58} 59