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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 | _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 */ |