111 lines
3.4 KiB
C++
111 lines
3.4 KiB
C++
// -*- coding: utf-8 -*-
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// Copyright (C) 2015, 2018 Laboratoire de Recherche et Développement
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// de l'Epita (LRDE)
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// Copyright (C) 2004, 2005 Laboratoire d'Informatique de Paris 6 (LIP6),
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// département Systèmes Répartis Coopératifs (SRC), Université Pierre
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// et Marie Curie.
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//
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// This file is part of Spot, a model checking library.
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//
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// Spot is free software; you can redistribute it and/or modify it
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// under the terms of the GNU General Public License as published by
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// the Free Software Foundation; either version 3 of the License, or
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// (at your option) any later version.
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//
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// Spot is distributed in the hope that it will be useful, but WITHOUT
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// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
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// License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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#pragma once
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#include <cstddef>
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#include <type_traits>
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namespace spot
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{
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/// \defgroup hash_funcs Hashing functions
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/// \ingroup misc_tools
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/// \ingroup hash_funcs
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/// @{
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/// \brief Thomas Wang's 32 bit hash function.
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///
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/// Hash an integer amongst the integers.
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/// http://web.archive.org/web/2011/concentric.net/~Ttwang/tech/inthash.htm
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inline size_t
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wang32_hash(size_t key)
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{
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// We assume that size_t has at least 32bits.
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key += ~(key << 15);
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key ^= (key >> 10);
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key += (key << 3);
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key ^= (key >> 6);
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key += ~(key << 11);
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key ^= (key >> 16);
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return key;
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}
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/// \brief Knuth's Multiplicative hash function.
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///
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/// This function is suitable for hashing values whose
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/// high order bits do not vary much (ex. addresses of
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/// memory objects). Prefer spot::wang32_hash() otherwise.
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/// http://web.archive.org/web/2011/concentric.net/~Ttwang/tech/addrhash.htm
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inline size_t
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knuth32_hash(size_t key)
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{
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// 2654435761 is the golden ratio of 2^32. The right shift of 3
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// bits assumes that all objects are aligned on a 8 byte boundary.
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return (key >> 3) * 2654435761U;
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}
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/// Struct for Fowler-Noll-Vo parameters
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template<class T, class Enable = void>
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struct fnv
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{};
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/// Fowler-Noll-Vo hash parameters for 32 bits
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template<class T>
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struct fnv<T, typename std::enable_if<sizeof(T) == 4>::type>
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{
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static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
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"Fowler-Noll-Vo hash requires an unsigned integral type");
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static constexpr T init = 2166136261UL;
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static constexpr T prime = 16777619UL;
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};
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/// Fowler-Noll-Vo hash parameters for 64 bits
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template<class T>
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struct fnv<T, typename std::enable_if<sizeof(T) == 8>::type>
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{
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static_assert(std::is_integral<T>::value && std::is_unsigned<T>::value,
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"Fowler-Noll-Vo hash requires an unsigned integral type");
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static constexpr T init = 14695981039346656037ULL;
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static constexpr T prime = 1099511628211ULL;
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};
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/// \brief Fowler-Noll-Vo hash function
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///
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/// This function is a non-cryptographic fast hash function.
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/// The magic constants depend on the size of a size_t.
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template<class It>
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size_t
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fnv_hash(It begin, It end)
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{
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size_t res = fnv<size_t>::init;
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for (; begin != end; ++begin)
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{
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res ^= *begin;
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res *= fnv<size_t>::prime;
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}
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return res;
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}
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/// @}
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}
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