| Brian Silverman | 8649792 | 2018-02-10 19:28:39 -0500 | [diff] [blame] | 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 */ |