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1 | // Licensed to the Apache Software Foundation (ASF) under one |
2 | // or more contributor license agreements. See the NOTICE file | |
3 | // distributed with this work for additional information | |
4 | // regarding copyright ownership. The ASF licenses this file | |
5 | // to you under the Apache License, Version 2.0 (the | |
6 | // "License"); you may not use this file except in compliance | |
7 | // with the License. You may obtain a copy of the License at | |
8 | // | |
9 | // http://www.apache.org/licenses/LICENSE-2.0 | |
10 | // | |
11 | // Unless required by applicable law or agreed to in writing, | |
12 | // software distributed under the License is distributed on an | |
13 | // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY | |
14 | // KIND, either express or implied. See the License for the | |
15 | // specific language governing permissions and limitations | |
16 | // under the License. | |
17 | ||
18 | #pragma once | |
19 | ||
20 | #include <cstdint> | |
21 | #include <type_traits> | |
22 | ||
23 | namespace arrow { | |
24 | namespace internal { | |
25 | ||
26 | /// \brief Metafunction to allow checking if a type matches any of another set of types | |
27 | template <typename...> | |
28 | struct IsOneOf : std::false_type {}; /// Base case: nothing has matched | |
29 | ||
30 | template <typename T, typename U, typename... Args> | |
31 | struct IsOneOf<T, U, Args...> { | |
32 | /// Recursive case: T == U or T matches any other types provided (not including U). | |
33 | static constexpr bool value = std::is_same<T, U>::value || IsOneOf<T, Args...>::value; | |
34 | }; | |
35 | ||
36 | /// \brief Shorthand for using IsOneOf + std::enable_if | |
37 | template <typename T, typename... Args> | |
38 | using EnableIfIsOneOf = typename std::enable_if<IsOneOf<T, Args...>::value, T>::type; | |
39 | ||
40 | /// \brief is_null_pointer from C++17 | |
41 | template <typename T> | |
42 | struct is_null_pointer : std::is_same<std::nullptr_t, typename std::remove_cv<T>::type> { | |
43 | }; | |
44 | ||
45 | #ifdef __GLIBCXX__ | |
46 | ||
47 | // A aligned_union backport, because old libstdc++ versions don't include it. | |
48 | ||
49 | constexpr std::size_t max_size(std::size_t a, std::size_t b) { return (a > b) ? a : b; } | |
50 | ||
51 | template <typename...> | |
52 | struct max_size_traits; | |
53 | ||
54 | template <typename H, typename... T> | |
55 | struct max_size_traits<H, T...> { | |
56 | static constexpr std::size_t max_sizeof() { | |
57 | return max_size(sizeof(H), max_size_traits<T...>::max_sizeof()); | |
58 | } | |
59 | static constexpr std::size_t max_alignof() { | |
60 | return max_size(alignof(H), max_size_traits<T...>::max_alignof()); | |
61 | } | |
62 | }; | |
63 | ||
64 | template <> | |
65 | struct max_size_traits<> { | |
66 | static constexpr std::size_t max_sizeof() { return 0; } | |
67 | static constexpr std::size_t max_alignof() { return 0; } | |
68 | }; | |
69 | ||
70 | template <std::size_t Len, typename... T> | |
71 | struct aligned_union { | |
72 | static constexpr std::size_t alignment_value = max_size_traits<T...>::max_alignof(); | |
73 | static constexpr std::size_t size_value = | |
74 | max_size(Len, max_size_traits<T...>::max_sizeof()); | |
75 | using type = typename std::aligned_storage<size_value, alignment_value>::type; | |
76 | }; | |
77 | ||
78 | #else | |
79 | ||
80 | template <std::size_t Len, typename... T> | |
81 | using aligned_union = std::aligned_union<Len, T...>; | |
82 | ||
83 | #endif | |
84 | ||
85 | } // namespace internal | |
86 | } // namespace arrow |