Line data Source code
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))
28 89079 : _dl_elf_hash (const char *name_arg)
29 : {
30 89079 : const unsigned char *name = (const unsigned char *) name_arg;
31 89079 : unsigned long int hash = *name;
32 89079 : if (hash != 0 && name[1] != '\0')
33 : {
34 89057 : hash = (hash << 4) + name[1];
35 89057 : if (name[2] != '\0')
36 : {
37 88876 : hash = (hash << 4) + name[2];
38 88876 : if (name[3] != '\0')
39 : {
40 87059 : hash = (hash << 4) + name[3];
41 87059 : if (name[4] != '\0')
42 : {
43 69041 : hash = (hash << 4) + name[4];
44 69041 : name += 5;
45 149483 : while (*name != '\0')
46 : {
47 : unsigned long int hi;
48 11401 : hash = (hash << 4) + *name++;
49 11401 : 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 11401 : hash ^= hi >> 24;
63 : }
64 :
65 : /* Second part of the modified formula. This
66 : operation can be lifted outside the loop. */
67 69041 : hash &= 0x0fffffff;
68 : }
69 : }
70 : }
71 : }
72 89079 : return hash;
73 : }
74 :
75 : #endif /* dl-hash.h */
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