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