lsst.cpputils
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include
lsst
cpputils
hashCombine.h
Go to the documentation of this file.
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/*
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* LSST Data Management System
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* See COPYRIGHT file at the top of the source tree.
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*
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* This product includes software developed by the
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* LSST Project (http://www.lsst.org/).
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*
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* This program is free software: you can redistribute it and/or modify
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* it 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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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the LSST License Statement and
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* the GNU General Public License along with this program. If not,
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* see <http://www.lsstcorp.org/LegalNotices/>.
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*/
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#ifndef LSST_CPPUTILS_HASH_COMBINE_H
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#define LSST_CPPUTILS_HASH_COMBINE_H
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#include <functional>
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namespace
lsst
{
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namespace
cpputils {
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inline
std::size_t
hashCombine
(
std::size_t
seed)
noexcept
{
return
seed; }
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// This implementation is provided by Matteo Italia, https://stackoverflow.com/a/38140932/834250
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// Algorithm described at https://stackoverflow.com/a/27952689
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// WARNING: should not be inline or constexpr; it can cause instantiation-order problems with std::hash<T>
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template
<
typename
T,
typename
... Rest>
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std::size_t
hashCombine
(
std::size_t
seed,
const
T& value, Rest... rest)
noexcept
{
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std::hash<T>
hasher;
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seed ^= hasher(value) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
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return
hashCombine
(seed, rest...);
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}
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// Note: not an overload of hashCombine to avoid ambiguity with hashCombine(size_t, T1, T2)
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// WARNING: should not be inline or constexpr; it can cause instantiation-order problems with std::hash<T>
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template
<
typename
InputIterator>
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std::size_t
hashIterable
(
std::size_t
seed, InputIterator begin, InputIterator end)
noexcept
{
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std::size_t
result = 0;
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for
(; begin != end; ++begin) {
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result =
hashCombine
(result, *begin);
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}
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return
result;
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}
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}
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namespace
utils = cpputils;
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}
// namespace lsst::cpputils
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#endif
std::hash
lsst::cpputils::hashCombine
std::size_t hashCombine(std::size_t seed) noexcept
Combine hashes.
Definition
hashCombine.h:35
lsst::cpputils::hashIterable
std::size_t hashIterable(std::size_t seed, InputIterator begin, InputIterator end) noexcept
Combine hashes in an iterable.
Definition
hashCombine.h:93
lsst
std::size_t
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