1 /* Compute hash value for given string according to ELF standard.
2 Copyright (C) 1995-2015 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 <http://www.gnu.org/licenses/>. */
18
19 #ifndef _DL_HASH_H
20 #define _DL_HASH_H 1
21
22
23 /* This is the hashing function specified by the ELF ABI. In the
24 first five operations no overflow is possible so we optimized it a
25 bit. */
26 static unsigned int
27 __attribute__ ((unused))
_dl_elf_hash(const char * name_arg)28 _dl_elf_hash (const char *name_arg)
29 {
30 const unsigned char *name = (const unsigned char *) name_arg;
31 unsigned long int hash = *name;
32 if (hash != 0 && name[1] != '\0')
33 {
34 hash = (hash << 4) + name[1];
35 if (name[2] != '\0')
36 {
37 hash = (hash << 4) + name[2];
38 if (name[3] != '\0')
39 {
40 hash = (hash << 4) + name[3];
41 if (name[4] != '\0')
42 {
43 hash = (hash << 4) + name[4];
44 name += 5;
45 while (*name != '\0')
46 {
47 unsigned long int hi;
48 hash = (hash << 4) + *name++;
49 hi = hash & 0xf0000000;
50
51 /* The algorithm specified in the ELF ABI is as
52 follows:
53
54 if (hi != 0)
55 hash ^= hi >> 24;
56
57 hash &= ~hi;
58
59 But the following is equivalent and a lot
60 faster, especially on modern processors. */
61
62 hash ^= hi >> 24;
63 }
64
65 /* Second part of the modified formula. This
66 operation can be lifted outside the loop. */
67 hash &= 0x0fffffff;
68 }
69 }
70 }
71 }
72 return hash;
73 }
74
75 #endif /* dl-hash.h */
76