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252b5132 RH |
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 | } |