/* Implement simple hashing table with string based keys. Copyright (C) 1994-2024 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. The GNU C Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with the GNU C Library; if not, see <https://www.gnu.org/licenses/>. */ #ifndef hashval_t # define hashval_t unsigned long int #endif #include <limits.h> /* For CHAR_BIT. */ hashval_t compute_hashval (const void *key, size_t keylen) { size_t cnt; hashval_t hval; /* Compute the hash value for the given string. The algorithm is taken from [Aho,Sethi,Ullman], modified to reduce the number of collisions for short strings with very varied bit patterns. See http://www.clisp.org/haible/hashfunc.html. */ cnt = 0; hval = keylen; while (cnt < keylen) { hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9)); hval += (hashval_t) ((const unsigned char *) key)[cnt++]; } return hval != 0 ? hval : ~((hashval_t) 0); }