1 /* Implements a string hashing function. 2 Copyright (C) 1995, 1997, 1998, 2000 Free Software Foundation, Inc. 3 This file is part of the GNU C Library. 4 5 The GNU C Library is free software; you can redistribute it and/or 6 modify it under the terms of the GNU Lesser General Public 7 License as published by the Free Software Foundation; either 8 version 2.1 of the License, or (at your option) any later version. 9 10 The GNU C Library is distributed in the hope that it will be useful, 11 but WITHOUT ANY WARRANTY; without even the implied warranty of 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 13 Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public 16 License along with the GNU C Library; if not, write to the Free 17 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 18 02111-1307 USA. */ 19 20 /* @@ end of prolog @@ */ 21 22 #ifndef PARAMS 23 # if __STDC__ || defined __GNUC__ || defined __SUNPRO_C || defined __cplusplus || __PROTOTYPES 24 # define PARAMS(Args) Args 25 # else 26 # define PARAMS(Args) () 27 # endif 28 #endif 29 30 /* We assume to have `unsigned long int' value with at least 32 bits. */ 31 #define HASHWORDBITS 32 32 33 34 /* Defines the so called `hashpjw' function by P.J. Weinberger 35 [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools, 36 1986, 1987 Bell Telephone Laboratories, Inc.] */ 37 static unsigned long int hash_string PARAMS ((const char *__str_param)); 38 39 static inline unsigned long int 40 hash_string (str_param) 41 const char *str_param; 42 { 43 unsigned long int hval, g; 44 const char *str = str_param; 45 46 /* Compute the hash value for the given string. */ 47 hval = 0; 48 while (*str != '\0') 49 { 50 hval <<= 4; 51 hval += (unsigned long int) *str++; 52 g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4)); 53 if (g != 0) 54 { 55 hval ^= g >> (HASHWORDBITS - 8); 56 hval ^= g; 57 } 58 } 59 return hval; 60 } 61