Ichthyostega
555af315b3
- remove obsolete configuration settings - walk through all settings according to the documentation https://www.doxygen.nl/manual/config.html - now try to use the new feature to rely on Clang for C++ parsing - walk through the doxygen-warnings.txt and fix some obvious misspellings and structural problems in the documentation comments. With Debian-Trixie, we are now using Doxygen 1.9.8 — which produces massively better results in various fine points. However, there are still problems with automatic cross links, especially from implementation to the corresponding test classes.
108 lines
4.1 KiB
C++
108 lines
4.1 KiB
C++
/*
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HASH-COMBINE.hpp - hash chaining function extracted from LibBoost
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Copyright (C)
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2012, Hermann Vosseler <Ichthyostega@web.de>
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**Lumiera** 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 the
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Free Software Foundation; either version 2 of the License, or (at your
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option) any later version. See the file COPYING for further details.
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======================================================================
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NOTE: this header adapts implementation code from LibBoost 1.67
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// Copyright 2005-2014 Daniel James.
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// Distributed under the Boost Software License, Version 1.0.
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// (See http://www.boost.org/LICENSE_1_0.txt)
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//
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// Based on Peter Dimov's proposal
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// http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2005/n1756.pdf
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// issue 6.18.
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//
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// This also contains public domain code from MurmurHash. From the MurmurHash header:
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//
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// MurmurHash3 was written by Austin Appleby, and is placed in the public
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// domain. The author hereby disclaims copyright to this source code.
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======================================================================
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*/
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/** @file hash-combine.hpp
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** Hash combine function extracted from LibBoost 1.67
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** Combine two hash values to form a composite depending on both.
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** @todo 2024 the Lumiera project has yet to decide how to approach
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** portability of hash values, and the related performance issues.
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** This code was directly integrated into the code base to ensure
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** a stable implementation and reproducible hash values.
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** ///////////////////////////////////////////////////////////////////////////////////////////////////TICKET #722 uniform uses of hash values
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*/
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#ifndef LIB_HASH_COMBINE_H
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#define LIB_HASH_COMBINE_H
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#include "lib/hash-value.h"
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#include "lib/integral.hpp"
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#include <climits>
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namespace lib {
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namespace hash{
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/** meld the additional hash value into the given base hash value.
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* This is the standard formula used by Lib-Boost to combine the hash values
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* of parts into a composite, and is based on the [Murmur-2.64A] hash algorithm.
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* [Murmur-2.64A]: https://github.com/aappleby/smhasher/blob/master/src/MurmurHash2.cpp
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*/
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inline void
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combine (size_t & combinedHash, size_t additionalHash)
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{
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#if false //////////////////////////////////////////////////////////////////////////////////////////////////TICKET #722 : Decide what stance to take towards portability
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combinedHash ^= additionalHash
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+ 0x9e3779b9
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+ (combinedHash<<6)
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+ (combinedHash>>2);
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}
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#endif /////////////////////////////////////////////////////////////////////////////////////////////////////TICKET #722 : (End) weak but portable fall-back code
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/////////////////////////////////////////////////////////////////////////////////////////////////////////TICKET #722 : Using the stronger Boost-impl for 64bit platforms
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//// see: Boost 1.67 <include>/boost/container_hash/hash.hpp
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///
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/*
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// Don't define 64-bit hash combine on platforms without 64 bit integers,
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// and also not for 32-bit gcc as it warns about the 64-bit constant.
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#if !defined(BOOST_NO_INT64_T) && \
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!(defined(__GNUC__) && ULONG_MAX == 0xffffffff)
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inline void hash_combine_impl(boost::uint64_t& h,
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boost::uint64_t k)
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{
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*/
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static_assert (sizeof (void*) * CHAR_BIT == 64, "TODO 2024 : decide what to do about portability");
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static_assert (sizeof (size_t) == sizeof(uint64_t));
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uint64_t& h = combinedHash;
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uint64_t k = additionalHash;
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const uint64_t m{0xc6a4a7935bd1e995};
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const int r = 47;
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k *= m;
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k ^= k >> r;
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k *= m;
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h ^= k;
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h *= m;
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// Completely arbitrary number, to prevent 0's
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// from hashing to 0.
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h += 0xe6546b64;
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}
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//////////////////////////////////////////////////////////////////////////////////////////////////////TICKET #722 : (End) Code extracted from Boost 1.67
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//
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//
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//
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}} // namespace lib::hash
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#endif /*LIB_HASH_COMBINE_H*/
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