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LSST Data Management Base Package
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hashCombine.h
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1/*
2 * LSST Data Management System
3 * See COPYRIGHT file at the top of the source tree.
4 *
5 * This product includes software developed by the
6 * LSST Project (http://www.lsst.org/).
7 *
8 * This program is free software: you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License as published by
10 * the Free Software Foundation, either version 3 of the License, or
11 * (at your option) any later version.
12 *
13 * This program is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 * GNU General Public License for more details.
17 *
18 * You should have received a copy of the LSST License Statement and
19 * the GNU General Public License along with this program. If not,
20 * see <http://www.lsstcorp.org/LegalNotices/>.
21 */
22#ifndef LSST_CPPUTILS_HASH_COMBINE_H
23#define LSST_CPPUTILS_HASH_COMBINE_H
24
25#include <functional>
26
27namespace lsst {
28namespace cpputils {
29
35inline std::size_t hashCombine(std::size_t seed) noexcept { return seed; }
36
59// This implementation is provided by Matteo Italia, https://stackoverflow.com/a/38140932/834250
60// Algorithm described at https://stackoverflow.com/a/27952689
61// WARNING: should not be inline or constexpr; it can cause instantiation-order problems with std::hash<T>
62template <typename T, typename... Rest>
63std::size_t hashCombine(std::size_t seed, const T& value, Rest... rest) noexcept {
64 std::hash<T> hasher;
65 seed ^= hasher(value) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
66 return hashCombine(seed, rest...);
67}
68
90// Note: not an overload of hashCombine to avoid ambiguity with hashCombine(size_t, T1, T2)
91// WARNING: should not be inline or constexpr; it can cause instantiation-order problems with std::hash<T>
92template <typename InputIterator>
93std::size_t hashIterable(std::size_t seed, InputIterator begin, InputIterator end) noexcept {
95 for (; begin != end; ++begin) {
96 result = hashCombine(result, *begin);
97 }
98 return result;
99}
100
101}
102namespace utils = cpputils;
103} // namespace lsst::cpputils
104
105#endif
py::object result
Definition _schema.cc:429
int end
std::size_t hashCombine(std::size_t seed) noexcept
Combine hashes.
Definition hashCombine.h:35
std::size_t hashIterable(std::size_t seed, InputIterator begin, InputIterator end) noexcept
Combine hashes in an iterable.
Definition hashCombine.h:93