1 /* hash-pjw-bare.c -- compute a hash value from a provided buffer. 2 3 Copyright (C) 2012-2021 Free Software Foundation, Inc. 4 5 This file is free software: you can redistribute it and/or modify 6 it under the terms of the GNU Lesser General Public License as 7 published by the Free Software Foundation; either version 2.1 of the 8 License, or (at your option) any later version. 9 10 This file 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 13 GNU Lesser General Public License for more details. 14 15 You should have received a copy of the GNU Lesser General Public License 16 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 17 18 #include <config.h> 19 20 #include "hash-pjw-bare.h" 21 22 #include <limits.h> 23 24 #define SIZE_BITS (sizeof (size_t) * CHAR_BIT) 25 26 /* Return a hash of the N bytes of X using the method described by 27 Bruno Haible in https://www.haible.de/bruno/hashfunc.html. 28 Note that while many hash functions reduce their result via modulo 29 to a 0..table_size-1 range, this function does not do that. */ 30 31 size_t 32 hash_pjw_bare (const void *x, size_t n) /* */ 33 { 34 const unsigned char *s = x; 35 size_t h = 0; 36 unsigned i; 37 38 for (i = 0; i < n; i++) 39 h = s[i] + ((h << 9) | (h >> (SIZE_BITS - 9))); 40 41 return h; 42 }