/* * Copyright (c) 2012 Adam Hraska * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * - Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * - The name of the author may not be used to endorse or promote products * derived from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ /** @addtogroup libc * @{ */ /** @file */ #ifndef _LIBC_ADT_HASH_H_ #define _LIBC_ADT_HASH_H_ #include <stddef.h> #include <stdint.h> /** Produces a uniform hash affecting all output bits from the skewed input. */ static inline uint32_t hash_mix32(uint32_t hash) { /* * Thomas Wang's modification of Bob Jenkin's hash mixing function: * http://www.concentric.net/~Ttwang/tech/inthash.htm * Public domain. */ hash = ~hash + (hash << 15); hash = hash ^ (hash >> 12); hash = hash + (hash << 2); hash = hash ^ (hash >> 4); hash = hash * 2057; hash = hash ^ (hash >> 16); return hash; } /** Produces a uniform hash affecting all output bits from the skewed input. */ static inline uint64_t hash_mix64(uint64_t hash) { /* * Thomas Wang's public domain 64-bit hash mixing function: * http://www.concentric.net/~Ttwang/tech/inthash.htm */ hash = (hash ^ 61) ^ (hash >> 16); hash = hash + (hash << 3); hash = hash ^ (hash >> 4); hash = hash * 0x27d4eb2d; hash = hash ^ (hash >> 15); /* * Lower order bits are mixed more thoroughly. Swap them with * the higher order bits and make the resulting higher order bits * more usable. */ return (hash << 32) | (hash >> 32); } /** Produces a uniform hash affecting all output bits from the skewed input. */ static inline size_t hash_mix(size_t hash) { if (sizeof(long) == 4) return hash_mix32(hash); else return hash_mix64(hash); } /** Use to create a hash from multiple values. * * Typical usage: * @code * int car_id; * bool car_convertible; * // .. * size_t hash = 0; * hash = hash_combine(hash, car_id); * hash = hash_combine(hash, car_convertible); * // Now use hash as a hash of both car_id and car_convertible. * @endcode */ static inline size_t hash_combine(size_t seed, size_t hash) { /* * todo: use Bob Jenkin's proper mixing hash pass: * http://burtleburtle.net/bob/c/lookup3.c */ seed ^= hash + 0x9e3779b9 + ((seed << 5) | (seed >> (sizeof(size_t) * 8 - 5))); return seed; } #endif