| 1 | /* Compute hash value for given string according to ELF standard. |
|---|
| 2 | Copyright (C) 1995, 1996, 1997, 1998 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, write to the Free |
|---|
| 17 | Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA |
|---|
| 18 | 02111-1307 USA. */ |
|---|
| 19 | |
|---|
| 20 | #ifndef _DL_HASH_H |
|---|
| 21 | #define _DL_HASH_H 1 |
|---|
| 22 | |
|---|
| 23 | |
|---|
| 24 | /* This is the hashing function specified by the ELF ABI. In the |
|---|
| 25 | first five operations no overflow is possible so we optimized it a |
|---|
| 26 | bit. */ |
|---|
| 27 | static inline unsigned int |
|---|
| 28 | _dl_elf_hash (const unsigned char *name) |
|---|
| 29 | { |
|---|
| 30 | unsigned long int hash = 0; |
|---|
| 31 | if (*name != '\0') |
|---|
| 32 | { |
|---|
| 33 | hash = *name++; |
|---|
| 34 | if (*name != '\0') |
|---|
| 35 | { |
|---|
| 36 | hash = (hash << 4) + *name++; |
|---|
| 37 | if (*name != '\0') |
|---|
| 38 | { |
|---|
| 39 | hash = (hash << 4) + *name++; |
|---|
| 40 | if (*name != '\0') |
|---|
| 41 | { |
|---|
| 42 | hash = (hash << 4) + *name++; |
|---|
| 43 | if (*name != '\0') |
|---|
| 44 | { |
|---|
| 45 | hash = (hash << 4) + *name++; |
|---|
| 46 | while (*name != '\0') |
|---|
| 47 | { |
|---|
| 48 | unsigned long int hi; |
|---|
| 49 | hash = (hash << 4) + *name++; |
|---|
| 50 | hi = hash & 0xf0000000; |
|---|
| 51 | |
|---|
| 52 | /* The algorithm specified in the ELF ABI is as |
|---|
| 53 | follows: |
|---|
| 54 | |
|---|
| 55 | if (hi != 0) |
|---|
| 56 | hash ^= hi >> 24; |
|---|
| 57 | |
|---|
| 58 | hash &= ~hi; |
|---|
| 59 | |
|---|
| 60 | But the following is equivalent and a lot |
|---|
| 61 | faster, especially on modern processors. */ |
|---|
| 62 | |
|---|
| 63 | hash ^= hi; |
|---|
| 64 | hash ^= hi >> 24; |
|---|
| 65 | } |
|---|
| 66 | } |
|---|
| 67 | } |
|---|
| 68 | } |
|---|
| 69 | } |
|---|
| 70 | } |
|---|
| 71 | return hash; |
|---|
| 72 | } |
|---|
| 73 | |
|---|
| 74 | #endif /* dl-hash.h */ |
|---|
