1 /* Implements hashing function for string with known length.
2 Copyright (C) 1996-2022 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, see
17 <https://www.gnu.org/licenses/>. */
18
19 #include <sys/types.h>
20
21 /* We assume to have `size_t' value with at least 32 bits. */
22 #define HASHWORDBITS 32
23
24
25 /* Defines the so called `hashpjw' function by P.J. Weinberger
26 [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
27 1986, 1987 Bell Telephone Laboratories, Inc.] */
28 static size_t hash_string (const char *__str_param, size_t __len);
29
30 static inline size_t
hash_string(const char * str_param,size_t len)31 hash_string (const char *str_param, size_t len)
32 {
33 size_t hval, g;
34 const char *end_str = str_param + len;
35
36 /* Compute the hash value for the given string. */
37 hval = len;
38 while (str_param != end_str)
39 {
40 hval <<= 4;
41 hval += (size_t) *str_param++;
42 g = hval & ((size_t) 0xf << (HASHWORDBITS - 4));
43 if (g != 0)
44 {
45 hval ^= g >> (HASHWORDBITS - 8);
46 hval ^= g;
47 }
48 }
49 return hval;
50 }
51