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c84142e8 UD |
1 | /* Implements hashing function for string with known length. |
2 | Copyright (C) 1996, 1997 Free Software Foundation, Inc. | |
41bdb6e2 | 3 | This file is part of the GNU C Library. |
c84142e8 UD |
4 | Contributed by Ulrich Drepper <drepper@cygnus.com>, 1996. |
5 | ||
6 | The GNU C Library is free software; you can redistribute it and/or | |
41bdb6e2 AJ |
7 | modify it under the terms of the GNU Lesser General Public |
8 | License as published by the Free Software Foundation; either | |
9 | version 2.1 of the License, or (at your option) any later version. | |
c84142e8 UD |
10 | |
11 | The GNU C Library is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
41bdb6e2 | 14 | Lesser General Public License for more details. |
c84142e8 | 15 | |
41bdb6e2 AJ |
16 | You should have received a copy of the GNU Lesser General Public |
17 | License along with the GNU C Library; if not, write to the Free | |
18 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA | |
19 | 02111-1307 USA. */ | |
ce7a5ef4 RM |
20 | |
21 | #include <sys/types.h> | |
22 | ||
23 | /* We assume to have `size_t' value with at least 32 bits. */ | |
24 | #define HASHWORDBITS 32 | |
25 | ||
26 | ||
27 | /* Defines the so called `hashpjw' function by P.J. Weinberger | |
28 | [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools, | |
29 | 1986, 1987 Bell Telephone Laboratories, Inc.] */ | |
30 | static size_t hash_string (const char *__str_param, size_t __len); | |
31 | ||
32 | static inline size_t | |
33 | hash_string (const char *str_param, size_t len) | |
34 | { | |
35 | size_t hval, g; | |
36 | const char *end_str = str_param + len; | |
37 | ||
38 | /* Compute the hash value for the given string. */ | |
39 | hval = len; | |
40 | while (str_param != end_str) | |
41 | { | |
42 | hval <<= 4; | |
43 | hval += (size_t) *str_param++; | |
44 | g = hval & ((size_t) 0xf << (HASHWORDBITS - 4)); | |
45 | if (g != 0) | |
46 | { | |
47 | hval ^= g >> (HASHWORDBITS - 8); | |
48 | hval ^= g; | |
49 | } | |
50 | } | |
51 | return hval; | |
52 | } |