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c84142e8 UD |
1 | /* Implements a string hashing function. |
2 | Copyright (C) 1995, 1997 Free Software Foundation, Inc. | |
24906b43 | 3 | |
c84142e8 UD |
4 | This file is part of the GNU C Library. Its master source is NOT part of |
5 | the C library, however. The master source lives in /gd/gnu/lib. | |
24906b43 | 6 | |
c84142e8 UD |
7 | The GNU C Library is free software; you can redistribute it and/or |
8 | modify it under the terms of the GNU Library General Public License as | |
9 | published by the Free Software Foundation; either version 2 of the | |
10 | License, or (at your option) any later version. | |
0393dfd6 | 11 | |
c84142e8 UD |
12 | The GNU C Library is distributed in the hope that it will be useful, |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
15 | Library General Public License for more details. | |
24906b43 | 16 | |
c84142e8 UD |
17 | You should have received a copy of the GNU Library General Public |
18 | License along with the GNU C Library; see the file COPYING.LIB. If not, | |
19 | write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, | |
20 | Boston, MA 02111-1307, USA. */ | |
24906b43 RM |
21 | |
22 | #ifdef HAVE_VALUES_H | |
23 | # include <values.h> | |
24 | #endif | |
25 | ||
26 | /* @@ end of prolog @@ */ | |
27 | ||
be10a868 RM |
28 | #ifndef PARAMS |
29 | # if __STDC__ | |
30 | # define PARAMS(Args) Args | |
31 | # else | |
32 | # define PARAMS(Args) () | |
33 | # endif | |
24906b43 RM |
34 | #endif |
35 | ||
be10a868 RM |
36 | /* We assume to have `unsigned long int' value with at least 32 bits. */ |
37 | #define HASHWORDBITS 32 | |
38 | ||
24906b43 RM |
39 | |
40 | /* Defines the so called `hashpjw' function by P.J. Weinberger | |
41 | [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools, | |
be10a868 RM |
42 | 1986, 1987 Bell Telephone Laboratories, Inc.] */ |
43 | static unsigned long hash_string PARAMS ((const char *__str_param)); | |
44 | ||
24906b43 RM |
45 | static inline unsigned long |
46 | hash_string (str_param) | |
47 | const char *str_param; | |
48 | { | |
be10a868 | 49 | unsigned long int hval, g; |
24906b43 RM |
50 | const char *str = str_param; |
51 | ||
52 | /* Compute the hash value for the given string. */ | |
53 | hval = 0; | |
54 | while (*str != '\0') | |
55 | { | |
56 | hval <<= 4; | |
57 | hval += (unsigned long) *str++; | |
be10a868 | 58 | g = hval & ((unsigned long) 0xf << (HASHWORDBITS - 4)); |
24906b43 RM |
59 | if (g != 0) |
60 | { | |
be10a868 | 61 | hval ^= g >> (HASHWORDBITS - 8); |
24906b43 RM |
62 | hval ^= g; |
63 | } | |
64 | } | |
65 | return hval; | |
66 | } |