projects / thirdparty / glibc.git / blame
| Commit | Line | Data |
|---|---|---|
| 118bad87 | 1 | /* Compute hash value for given string according to ELF standard. |
| b168057a | 2 | Copyright (C) 1995-2015 Free Software Foundation, Inc. |
| 1fb05e3d UD |
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 | |
| 41bdb6e2 AJ |
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. | |
| 1fb05e3d UD |
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 | |
| 41bdb6e2 | 13 | Lesser General Public License for more details. |
| 1fb05e3d | 14 | |
| 41bdb6e2 | 15 | You should have received a copy of the GNU Lesser General Public |
| 59ba27a6 PE |
16 | License along with the GNU C Library; if not, see |
| 17 | <http://www.gnu.org/licenses/>. */ | |
| 1fb05e3d UD |
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 | |
| 85f72e9c | 24 | first five operations no overflow is possible so we optimized it a |
| 1fb05e3d | 25 | bit. */ |
| 50441a98 | 26 | static unsigned int |
| 52ff5dd0 | 27 | __attribute__ ((unused)) |
| 9cfe5381 | 28 | _dl_elf_hash (const char *name_arg) |
| 1fb05e3d | 29 | { |
| 9cfe5381 | 30 | const unsigned char *name = (const unsigned char *) name_arg; |
| 52ad36a2 UD |
31 | unsigned long int hash = *name; |
| 32 | if (hash != 0 && name[1] != '\0') | |
| 1fb05e3d | 33 | { |
| 52ad36a2 UD |
34 | hash = (hash << 4) + name[1]; |
| 35 | if (name[2] != '\0') | |
| 1fb05e3d | 36 | { |
| 52ad36a2 UD |
37 | hash = (hash << 4) + name[2]; |
| 38 | if (name[3] != '\0') | |
| 1fb05e3d | 39 | { |
| 52ad36a2 UD |
40 | hash = (hash << 4) + name[3]; |
| 41 | if (name[4] != '\0') | |
| 1fb05e3d | 42 | { |
| 52ad36a2 UD |
43 | hash = (hash << 4) + name[4]; |
| 44 | name += 5; | |
| 45 | while (*name != '\0') | |
| 1fb05e3d | 46 | { |
| 52ad36a2 | 47 | unsigned long int hi; |
| 1fb05e3d | 48 | hash = (hash << 4) + *name++; |
| 52ad36a2 | 49 | hi = hash & 0xf0000000; |
| 85f72e9c | 50 | |
| 52ad36a2 UD |
51 | /* The algorithm specified in the ELF ABI is as |
| 52 | follows: | |
| 85f72e9c | 53 | |
| 52ad36a2 UD |
54 | if (hi != 0) |
| 55 | hash ^= hi >> 24; | |
| 85f72e9c | 56 | |
| 52ad36a2 | 57 | hash &= ~hi; |
| 85f72e9c | 58 | |
| 52ad36a2 UD |
59 | But the following is equivalent and a lot |
| 60 | faster, especially on modern processors. */ | |
| 85f72e9c | 61 | |
| 52ad36a2 | 62 | hash ^= hi >> 24; |
| 1fb05e3d | 63 | } |
| f039c043 UD |
64 | |
| 65 | /* Second part of the modified formula. This | |
| 66 | operation can be lifted outside the loop. */ | |
| 67 | hash &= 0x0fffffff; | |
| 1fb05e3d UD |
68 | } |
| 69 | } | |
| 70 | } | |
| 71 | } | |
| 72 | return hash; | |
| 73 | } | |
| 74 | ||
| 75 | #endif /* dl-hash.h */ |