1 /* Implements a string hashing function. 2 Copyright (C) 1995, 1997 Free Software Foundation, Inc. 3 4 This program is free software; you can redistribute it and/or modify 5 it under the terms of the GNU General Public License as published by 6 the Free Software Foundation; either version 2, or (at your option) 7 any later version. 8 9 This program is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU General Public License for more details. 13 14 You should have received a copy of the GNU Library General Public 15 License along with the GNU C Library; see the file COPYING.LIB. If not, 16 write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, 17 Boston, MA 02111-1307, USA. */ 18 19 #ifdef HAVE_VALUES_H 20 # include <values.h> 21 #endif 22 23 /* @@ end of prolog @@ */ 24 25 #ifndef PARAMS 26 # if __STDC__ 27 # define PARAMS(Args) Args 28 # else 29 # define PARAMS(Args) () 30 # endif 31 #endif 32 33 /* We assume to have `unsigned long int' value with at least 32 bits. */ 34 #define HASHWORDBITS 32 35 36 37 /* Defines the so called `hashpjw' function by P.J. Weinberger 38 [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools, 39 1986, 1987 Bell Telephone Laboratories, Inc.] */ 40 static unsigned long hash_string PARAMS ((const char *__str_param)); 41 42 static inline unsigned long 43 hash_string (str_param) 44 const char *str_param; 45 { 46 unsigned long int hval, g; 47 const char *str = str_param; 48 49 /* Compute the hash value for the given string. */ 50 hval = 0; 51 while (*str != '\0') 52 { 53 hval <<= 4; 54 hval += (unsigned long) *str++; 55 g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4)); 56 if (g != 0) 57 { 58 hval ^= g >> (HASHWORDBITS - 8); 59 hval ^= g; 60 } 61 } 62 return hval; 63 } 64