| 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 | } |