| xf.li | bdd93d5 | 2023-05-12 07:10:14 -0700 | [diff] [blame^] | 1 | /* Implement simple hashing table with string based keys. |
| 2 | Copyright (C) 1994-2016 Free Software Foundation, Inc. |
| 3 | This file is part of the GNU C Library. |
| 4 | Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994. |
| 5 | |
| 6 | The GNU C Library is free software; you can redistribute it and/or |
| 7 | modify it under the terms of the GNU Lesser General Public |
| 8 | License as published by the Free Software Foundation; either |
| 9 | version 2.1 of the License, or (at your option) any later version. |
| 10 | |
| 11 | The GNU C Library is distributed in the hope that it will be useful, |
| 12 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| 14 | Lesser General Public License for more details. |
| 15 | |
| 16 | You should have received a copy of the GNU Lesser General Public |
| 17 | License along with the GNU C Library; if not, see |
| 18 | <http://www.gnu.org/licenses/>. */ |
| 19 | |
| 20 | #ifndef hashval_t |
| 21 | # define hashval_t unsigned long int |
| 22 | #endif |
| 23 | #include <limits.h> /* For CHAR_BIT. */ |
| 24 | |
| 25 | hashval_t |
| 26 | compute_hashval (const void *key, size_t keylen) |
| 27 | { |
| 28 | size_t cnt; |
| 29 | hashval_t hval; |
| 30 | |
| 31 | /* Compute the hash value for the given string. The algorithm |
| 32 | is taken from [Aho,Sethi,Ullman], modified to reduce the number of |
| 33 | collisions for short strings with very varied bit patterns. |
| 34 | See http://www.clisp.org/haible/hashfunc.html. */ |
| 35 | cnt = 0; |
| 36 | hval = keylen; |
| 37 | while (cnt < keylen) |
| 38 | { |
| 39 | hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9)); |
| 40 | hval += (hashval_t) ((const unsigned char *) key)[cnt++]; |
| 41 | } |
| 42 | return hval != 0 ? hval : ~((hashval_t) 0); |
| 43 | } |