1/*
2 * Copyright (C) 2016 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17#ifndef STAGEFRIGHT_FOUNDATION_TYPE_TRAITS_H_
18#define STAGEFRIGHT_FOUNDATION_TYPE_TRAITS_H_
19
20#include <type_traits>
21
22namespace android {
23
24/**
25 * std::is_signed, is_unsigned and is_integral does not consider enums even though the standard
26 * considers them integral. Create modified versions of these here. Also create a wrapper around
27 * std::underlying_type that does not require checking if the type is an enum.
28 */
29
30/**
31 * Type support utility class to check if a type is an integral type or an enum.
32 */
33template<typename T>
34struct is_integral_or_enum
35    : std::integral_constant<bool, std::is_integral<T>::value || std::is_enum<T>::value> { };
36
37/**
38 * Type support utility class to get the underlying std::is_integral supported type for a type.
39 * This returns the underlying type for enums, and the same type for types covered by
40 * std::is_integral.
41 *
42 * This is also used as a conditional to return an alternate type if the template param is not
43 * an integral or enum type (as in underlying_integral_type<T, TypeIfNotEnumOrIntegral>::type).
44 */
45template<typename T,
46        typename U=typename std::enable_if<is_integral_or_enum<T>::value>::type,
47        bool=std::is_enum<T>::value,
48        bool=std::is_integral<T>::value>
49struct underlying_integral_type {
50    static_assert(!std::is_enum<T>::value, "T should not be enum here");
51    static_assert(!std::is_integral<T>::value, "T should not be integral here");
52    typedef U type;
53};
54
55/** Specialization for enums. */
56template<typename T, typename U>
57struct underlying_integral_type<T, U, true, false> {
58    static_assert(std::is_enum<T>::value, "T should be enum here");
59    static_assert(!std::is_integral<T>::value, "T should not be integral here");
60    typedef typename std::underlying_type<T>::type type;
61};
62
63/** Specialization for non-enum std-integral types. */
64template<typename T, typename U>
65struct underlying_integral_type<T, U, false, true> {
66    static_assert(!std::is_enum<T>::value, "T should not be enum here");
67    static_assert(std::is_integral<T>::value, "T should be integral here");
68    typedef T type;
69};
70
71/**
72 * Type support utility class to check if the underlying integral type is signed.
73 */
74template<typename T>
75struct is_signed_integral
76    : std::integral_constant<bool, std::is_signed<
77            typename underlying_integral_type<T, unsigned>::type>::value> { };
78
79/**
80 * Type support utility class to check if the underlying integral type is unsigned.
81 */
82template<typename T>
83struct is_unsigned_integral
84    : std::integral_constant<bool, std::is_unsigned<
85            typename underlying_integral_type<T, signed>::type>::value> {
86};
87
88/**
89 * Type support relationship query template.
90 *
91 * If T occurs as one of the types in Us with the same const-volatile qualifications, provides the
92 * member constant |value| equal to true. Otherwise value is false.
93 */
94template<typename T, typename ...Us>
95struct is_one_of;
96
97/// \if 0
98/**
99 * Template specialization when first type matches the searched type.
100 */
101template<typename T, typename ...Us>
102struct is_one_of<T, T, Us...> : std::true_type {};
103
104/**
105 * Template specialization when first type does not match the searched type.
106 */
107template<typename T, typename U, typename ...Us>
108struct is_one_of<T, U, Us...> : is_one_of<T, Us...> {};
109
110/**
111 * Template specialization when there are no types to search.
112 */
113template<typename T>
114struct is_one_of<T> : std::false_type {};
115/// \endif
116
117/**
118 * Type support relationship query template.
119 *
120 * If all types in Us are unique, provides the member constant |value| equal to true.
121 * Otherwise value is false.
122 */
123template<typename ...Us>
124struct are_unique;
125
126/// \if 0
127/**
128 * Template specialization when there are no types.
129 */
130template<>
131struct are_unique<> : std::true_type {};
132
133/**
134 * Template specialization when there is at least one type to check.
135 */
136template<typename T, typename ...Us>
137struct are_unique<T, Us...>
138    : std::integral_constant<bool, are_unique<Us...>::value && !is_one_of<T, Us...>::value> {};
139/// \endif
140
141/// \if 0
142template<size_t Base, typename T, typename ...Us>
143struct _find_first_impl;
144
145/**
146 * Template specialization when there are no types to search.
147 */
148template<size_t Base, typename T>
149struct _find_first_impl<Base, T> : std::integral_constant<size_t, 0> {};
150
151/**
152 * Template specialization when T is the first type in Us.
153 */
154template<size_t Base, typename T, typename ...Us>
155struct _find_first_impl<Base, T, T, Us...> : std::integral_constant<size_t, Base> {};
156
157/**
158 * Template specialization when T is not the first type in Us.
159 */
160template<size_t Base, typename T, typename U, typename ...Us>
161struct _find_first_impl<Base, T, U, Us...>
162    : std::integral_constant<size_t, _find_first_impl<Base + 1, T, Us...>::value> {};
163
164/// \endif
165
166/**
167 * Type support relationship query template.
168 *
169 * If T occurs in Us, index is the 1-based left-most index of T in Us. Otherwise, index is 0.
170 */
171template<typename T, typename ...Us>
172struct find_first {
173    static constexpr size_t index = _find_first_impl<1, T, Us...>::value;
174};
175
176/// \if 0
177/**
178 * Helper class for find_first_convertible_to template.
179 *
180 * Adds a base index.
181 */
182template<size_t Base, typename T, typename ...Us>
183struct _find_first_convertible_to_helper;
184
185/**
186 * Template specialization for when there are more types to consider
187 */
188template<size_t Base, typename T, typename U, typename ...Us>
189struct _find_first_convertible_to_helper<Base, T, U, Us...> {
190    static constexpr size_t index =
191        std::is_convertible<T, U>::value ? Base :
192                _find_first_convertible_to_helper<Base + 1, T, Us...>::index;
193    typedef typename std::conditional<
194        std::is_convertible<T, U>::value, U,
195        typename _find_first_convertible_to_helper<Base + 1, T, Us...>::type>::type type;
196};
197
198/**
199 * Template specialization for when there are no more types to consider
200 */
201template<size_t Base, typename T>
202struct _find_first_convertible_to_helper<Base, T> {
203    static constexpr size_t index = 0;
204    typedef void type;
205};
206
207/// \endif
208
209/**
210 * Type support template that returns the type that T can be implicitly converted into, and its
211 * index, from a list of other types (Us).
212 *
213 * Returns index of 0 and type of void if there are no convertible types.
214 *
215 * \param T type that is converted
216 * \param Us types into which the conversion is considered
217 */
218template<typename T, typename ...Us>
219struct find_first_convertible_to : public _find_first_convertible_to_helper<1, T, Us...> { };
220
221}  // namespace android
222
223#endif  // STAGEFRIGHT_FOUNDATION_TYPE_TRAITS_H_
224
225