1 /* Compute hash value for given string according to ELF standard.
2 Copyright (C) 2006 Red Hat, Inc.
3 This file is part of elfutils.
4 Written by Ulrich Drepper <drepper@redhat.com>, 1995.
5
6 This file is free software; you can redistribute it and/or modify
7 it under the terms of either
8
9 * the GNU Lesser General Public License as published by the Free
10 Software Foundation; either version 3 of the License, or (at
11 your option) any later version
12
13 or
14
15 * the GNU General Public License as published by the Free
16 Software Foundation; either version 2 of the License, or (at
17 your option) any later version
18
19 or both in parallel, as here.
20
21 elfutils is distributed in the hope that it will be useful, but
22 WITHOUT ANY WARRANTY; without even the implied warranty of
23 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
24 General Public License for more details.
25
26 You should have received copies of the GNU General Public License and
27 the GNU Lesser General Public License along with this program. If
28 not, see <http://www.gnu.org/licenses/>. */
29
30 #ifndef _DL_HASH_H
31 #define _DL_HASH_H 1
32
33
34 /* This is the hashing function specified by the ELF ABI. In the
35 first five operations no overflow is possible so we optimized it a
36 bit. */
37 static inline unsigned int
38 __attribute__ ((__pure__))
_dl_elf_hash(const char * name)39 _dl_elf_hash (const char *name)
40 {
41 const unsigned char *iname = (const unsigned char *) name;
42 unsigned int hash = (unsigned int) *iname++;
43 if (*iname != '\0')
44 {
45 hash = (hash << 4) + (unsigned int) *iname++;
46 if (*iname != '\0')
47 {
48 hash = (hash << 4) + (unsigned int) *iname++;
49 if (*iname != '\0')
50 {
51 hash = (hash << 4) + (unsigned int) *iname++;
52 if (*iname != '\0')
53 {
54 hash = (hash << 4) + (unsigned int) *iname++;
55 while (*iname != '\0')
56 {
57 unsigned int hi;
58 hash = (hash << 4) + (unsigned int) *iname++;
59 hi = hash & 0xf0000000;
60
61 /* The algorithm specified in the ELF ABI is as
62 follows:
63
64 if (hi != 0)
65 hash ^= hi >> 24;
66
67 hash &= ~hi;
68
69 But the following is equivalent and a lot
70 faster, especially on modern processors. */
71
72 hash ^= hi;
73 hash ^= hi >> 24;
74 }
75 }
76 }
77 }
78 }
79 return hash;
80 }
81
82 #endif /* dl-hash.h */
83