Dominik Laskowski | 0bacf27 | 2020-10-22 14:08:27 -0700 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2020 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 | #pragma once |
| 18 | |
| 19 | #include <ftl/ArrayTraits.h> |
| 20 | #include <ftl/StaticVector.h> |
| 21 | |
| 22 | #include <algorithm> |
| 23 | #include <iterator> |
| 24 | #include <type_traits> |
| 25 | #include <utility> |
| 26 | #include <variant> |
| 27 | #include <vector> |
| 28 | |
| 29 | namespace android::ftl { |
| 30 | |
| 31 | template <typename> |
| 32 | struct IsSmallVector; |
| 33 | |
| 34 | // ftl::StaticVector that promotes to std::vector when full. SmallVector is a drop-in replacement |
| 35 | // for std::vector with statically allocated storage for N elements, whose goal is to improve run |
| 36 | // time by avoiding heap allocation and increasing probability of cache hits. The standard API is |
| 37 | // augmented by an unstable_erase operation that does not preserve order, and a replace operation |
| 38 | // that destructively emplaces. |
| 39 | // |
| 40 | // SmallVector<T, 0> is a specialization that thinly wraps std::vector. |
| 41 | // |
| 42 | // Example usage: |
| 43 | // |
| 44 | // ftl::SmallVector<char, 3> vector; |
| 45 | // assert(vector.empty()); |
| 46 | // assert(!vector.dynamic()); |
| 47 | // |
| 48 | // vector = {'a', 'b', 'c'}; |
| 49 | // assert(vector.size() == 3u); |
| 50 | // assert(!vector.dynamic()); |
| 51 | // |
| 52 | // vector.push_back('d'); |
| 53 | // assert(vector.dynamic()); |
| 54 | // |
| 55 | // vector.unstable_erase(vector.begin()); |
| 56 | // assert(vector == (ftl::SmallVector{'d', 'b', 'c'})); |
| 57 | // |
| 58 | // vector.pop_back(); |
| 59 | // assert(vector.back() == 'b'); |
| 60 | // assert(vector.dynamic()); |
| 61 | // |
| 62 | // const char array[] = "hi"; |
| 63 | // vector = ftl::SmallVector(array); |
| 64 | // assert(vector == (ftl::SmallVector{'h', 'i', '\0'})); |
| 65 | // assert(!vector.dynamic()); |
| 66 | // |
| 67 | template <typename T, size_t N> |
| 68 | class SmallVector final : ArrayTraits<T>, ArrayComparators<SmallVector> { |
| 69 | using Static = StaticVector<T, N>; |
| 70 | using Dynamic = SmallVector<T, 0>; |
| 71 | |
| 72 | // TODO: Replace with std::remove_cvref_t in C++20. |
| 73 | template <typename U> |
| 74 | using remove_cvref_t = std::remove_cv_t<std::remove_reference_t<U>>; |
| 75 | |
| 76 | public: |
| 77 | FTL_ARRAY_TRAIT(T, value_type); |
| 78 | FTL_ARRAY_TRAIT(T, size_type); |
| 79 | FTL_ARRAY_TRAIT(T, difference_type); |
| 80 | |
| 81 | FTL_ARRAY_TRAIT(T, pointer); |
| 82 | FTL_ARRAY_TRAIT(T, reference); |
| 83 | FTL_ARRAY_TRAIT(T, iterator); |
| 84 | FTL_ARRAY_TRAIT(T, reverse_iterator); |
| 85 | |
| 86 | FTL_ARRAY_TRAIT(T, const_pointer); |
| 87 | FTL_ARRAY_TRAIT(T, const_reference); |
| 88 | FTL_ARRAY_TRAIT(T, const_iterator); |
| 89 | FTL_ARRAY_TRAIT(T, const_reverse_iterator); |
| 90 | |
| 91 | // Creates an empty vector. |
| 92 | SmallVector() = default; |
| 93 | |
| 94 | // Constructs at most N elements. See StaticVector for underlying constructors. |
| 95 | template <typename Arg, typename... Args, |
| 96 | typename = std::enable_if_t<!IsSmallVector<remove_cvref_t<Arg>>{}>> |
| 97 | SmallVector(Arg&& arg, Args&&... args) |
| 98 | : mVector(std::in_place_type<Static>, std::forward<Arg>(arg), |
| 99 | std::forward<Args>(args)...) {} |
| 100 | |
| 101 | // Copies at most N elements from a smaller convertible vector. |
| 102 | template <typename U, size_t M, typename = std::enable_if_t<M <= N>> |
| 103 | SmallVector(const SmallVector<U, M>& other) |
| 104 | : SmallVector(IteratorRange, other.begin(), other.end()) {} |
| 105 | |
| 106 | void swap(SmallVector& other) { mVector.swap(other.mVector); } |
| 107 | |
| 108 | // Returns whether the vector is backed by static or dynamic storage. |
| 109 | bool dynamic() const { return std::holds_alternative<Dynamic>(mVector); } |
| 110 | |
| 111 | #define VISITOR(T, F, ...) \ |
| 112 | T F() __VA_ARGS__ { \ |
| 113 | return std::visit([](auto&& v) -> T { return v.F(); }, mVector); \ |
| 114 | } |
| 115 | |
| 116 | VISITOR(size_type, max_size, const) |
| 117 | VISITOR(size_type, size, const) |
| 118 | VISITOR(bool, empty, const) |
| 119 | |
| 120 | // noexcept to suppress warning about zero variadic macro arguments. |
| 121 | VISITOR(iterator, begin, noexcept) |
| 122 | VISITOR(const_iterator, begin, const) |
| 123 | VISITOR(const_iterator, cbegin, const) |
| 124 | |
| 125 | VISITOR(iterator, end, noexcept) |
| 126 | VISITOR(const_iterator, end, const) |
| 127 | VISITOR(const_iterator, cend, const) |
| 128 | |
| 129 | VISITOR(reverse_iterator, rbegin, noexcept) |
| 130 | VISITOR(const_reverse_iterator, rbegin, const) |
| 131 | VISITOR(const_reverse_iterator, crbegin, const) |
| 132 | |
| 133 | VISITOR(reverse_iterator, rend, noexcept) |
| 134 | VISITOR(const_reverse_iterator, rend, const) |
| 135 | VISITOR(const_reverse_iterator, crend, const) |
| 136 | |
| 137 | VISITOR(iterator, last, noexcept) |
| 138 | VISITOR(const_iterator, last, const) |
| 139 | |
| 140 | VISITOR(reference, front, noexcept) |
| 141 | VISITOR(const_reference, front, const) |
| 142 | |
| 143 | VISITOR(reference, back, noexcept) |
| 144 | VISITOR(const_reference, back, const) |
| 145 | |
| 146 | #undef VISITOR |
| 147 | |
| 148 | reference operator[](size_type i) { |
| 149 | return std::visit([i](auto& v) -> reference { return v[i]; }, mVector); |
| 150 | } |
| 151 | |
| 152 | const_reference operator[](size_type i) const { |
| 153 | return std::visit([i](const auto& v) -> const_reference { return v[i]; }, mVector); |
| 154 | } |
| 155 | |
| 156 | // Replaces an element, and returns a reference to it. The iterator must be dereferenceable, so |
| 157 | // replacing at end() is erroneous. |
| 158 | // |
| 159 | // The element is emplaced via move constructor, so type T does not need to define copy/move |
| 160 | // assignment, e.g. its data members may be const. |
| 161 | // |
| 162 | // The arguments may directly or indirectly refer to the element being replaced. |
| 163 | // |
| 164 | // Iterators to the replaced element point to its replacement, and others remain valid. |
| 165 | // |
| 166 | template <typename... Args> |
| 167 | reference replace(const_iterator it, Args&&... args) { |
| 168 | return std:: |
| 169 | visit([it, &args...](auto& v) |
| 170 | -> reference { return v.replace(it, std::forward<Args>(args)...); }, |
| 171 | mVector); |
| 172 | } |
| 173 | |
| 174 | // Appends an element, and returns a reference to it. |
| 175 | // |
| 176 | // If the vector reaches its static or dynamic capacity, then all iterators are invalidated. |
| 177 | // Otherwise, only the end() iterator is invalidated. |
| 178 | // |
| 179 | template <typename... Args> |
| 180 | reference emplace_back(Args&&... args) { |
| 181 | constexpr auto insertStatic = &Static::template emplace_back<Args...>; |
| 182 | constexpr auto insertDynamic = &Dynamic::template emplace_back<Args...>; |
| 183 | return *insert<insertStatic, insertDynamic>(std::forward<Args>(args)...); |
| 184 | } |
| 185 | |
| 186 | // Appends an element. |
| 187 | // |
| 188 | // If the vector reaches its static or dynamic capacity, then all iterators are invalidated. |
| 189 | // Otherwise, only the end() iterator is invalidated. |
| 190 | // |
| 191 | void push_back(const value_type& v) { |
| 192 | constexpr auto insertStatic = |
| 193 | static_cast<bool (Static::*)(const value_type&)>(&Static::push_back); |
| 194 | constexpr auto insertDynamic = |
| 195 | static_cast<bool (Dynamic::*)(const value_type&)>(&Dynamic::push_back); |
| 196 | insert<insertStatic, insertDynamic>(v); |
| 197 | } |
| 198 | |
| 199 | void push_back(value_type&& v) { |
| 200 | constexpr auto insertStatic = |
| 201 | static_cast<bool (Static::*)(value_type&&)>(&Static::push_back); |
| 202 | constexpr auto insertDynamic = |
| 203 | static_cast<bool (Dynamic::*)(value_type&&)>(&Dynamic::push_back); |
| 204 | insert<insertStatic, insertDynamic>(std::move(v)); |
| 205 | } |
| 206 | |
| 207 | // Removes the last element. The vector must not be empty, or the call is erroneous. |
| 208 | // |
| 209 | // The last() and end() iterators are invalidated. |
| 210 | // |
| 211 | void pop_back() { |
| 212 | std::visit([](auto& v) { v.pop_back(); }, mVector); |
| 213 | } |
| 214 | |
| 215 | // Erases an element, but does not preserve order. Rather than shifting subsequent elements, |
| 216 | // this moves the last element to the slot of the erased element. |
| 217 | // |
| 218 | // The last() and end() iterators, as well as those to the erased element, are invalidated. |
| 219 | // |
| 220 | void unstable_erase(iterator it) { |
| 221 | std::visit([it](auto& v) { v.unstable_erase(it); }, mVector); |
| 222 | } |
| 223 | |
| 224 | private: |
| 225 | template <typename... Vs> |
| 226 | struct Visitor : Vs... {}; |
| 227 | |
| 228 | // TODO: Remove this deduction guide in C++20. |
| 229 | template <typename... Vs> |
| 230 | Visitor(Vs...) -> Visitor<Vs...>; |
| 231 | |
| 232 | template <auto insertStatic, auto insertDynamic, typename... Args> |
| 233 | auto insert(Args&&... args) { |
| 234 | return std::visit(Visitor{[this, &args...](Static& vector) { |
| 235 | if (vector.full()) { |
| 236 | return (promote(vector).* |
| 237 | insertDynamic)(std::forward<Args>(args)...); |
| 238 | } |
| 239 | |
| 240 | return (vector.*insertStatic)(std::forward<Args>(args)...); |
| 241 | }, |
| 242 | [&args...](Dynamic& vector) { |
| 243 | return (vector.*insertDynamic)(std::forward<Args>(args)...); |
| 244 | }}, |
| 245 | mVector); |
| 246 | } |
| 247 | |
| 248 | Dynamic& promote(Static& staticVector) { |
| 249 | assert(staticVector.full()); |
| 250 | |
| 251 | // Allocate double capacity to reduce probability of reallocation. |
| 252 | Dynamic vector; |
| 253 | vector.reserve(Static::max_size() * 2); |
| 254 | std::move(staticVector.begin(), staticVector.end(), std::back_inserter(vector)); |
| 255 | |
| 256 | return mVector.template emplace<Dynamic>(std::move(vector)); |
| 257 | } |
| 258 | |
| 259 | std::variant<Static, Dynamic> mVector; |
| 260 | }; |
| 261 | |
| 262 | // Partial specialization without static storage. |
| 263 | template <typename T> |
| 264 | class SmallVector<T, 0> final : ArrayTraits<T>, |
| 265 | ArrayIterators<SmallVector<T, 0>, T>, |
| 266 | std::vector<T> { |
| 267 | using ArrayTraits<T>::construct_at; |
| 268 | |
| 269 | using Iter = ArrayIterators<SmallVector, T>; |
| 270 | using Impl = std::vector<T>; |
| 271 | |
| 272 | friend Iter; |
| 273 | |
| 274 | public: |
| 275 | FTL_ARRAY_TRAIT(T, value_type); |
| 276 | FTL_ARRAY_TRAIT(T, size_type); |
| 277 | FTL_ARRAY_TRAIT(T, difference_type); |
| 278 | |
| 279 | FTL_ARRAY_TRAIT(T, pointer); |
| 280 | FTL_ARRAY_TRAIT(T, reference); |
| 281 | FTL_ARRAY_TRAIT(T, iterator); |
| 282 | FTL_ARRAY_TRAIT(T, reverse_iterator); |
| 283 | |
| 284 | FTL_ARRAY_TRAIT(T, const_pointer); |
| 285 | FTL_ARRAY_TRAIT(T, const_reference); |
| 286 | FTL_ARRAY_TRAIT(T, const_iterator); |
| 287 | FTL_ARRAY_TRAIT(T, const_reverse_iterator); |
| 288 | |
| 289 | using Impl::Impl; |
| 290 | |
| 291 | using Impl::empty; |
| 292 | using Impl::max_size; |
| 293 | using Impl::size; |
| 294 | |
| 295 | using Impl::reserve; |
| 296 | |
| 297 | // std::vector iterators are not necessarily raw pointers. |
| 298 | iterator begin() { return Impl::data(); } |
| 299 | iterator end() { return Impl::data() + size(); } |
| 300 | |
| 301 | using Iter::begin; |
| 302 | using Iter::end; |
| 303 | |
| 304 | using Iter::cbegin; |
| 305 | using Iter::cend; |
| 306 | |
| 307 | using Iter::rbegin; |
| 308 | using Iter::rend; |
| 309 | |
| 310 | using Iter::crbegin; |
| 311 | using Iter::crend; |
| 312 | |
| 313 | using Iter::last; |
| 314 | |
| 315 | using Iter::back; |
| 316 | using Iter::front; |
| 317 | |
| 318 | using Iter::operator[]; |
| 319 | |
| 320 | template <typename... Args> |
| 321 | reference replace(const_iterator it, Args&&... args) { |
| 322 | value_type element{std::forward<Args>(args)...}; |
| 323 | std::destroy_at(it); |
| 324 | // This is only safe because exceptions are disabled. |
| 325 | return *construct_at(it, std::move(element)); |
| 326 | } |
| 327 | |
| 328 | template <typename... Args> |
| 329 | iterator emplace_back(Args&&... args) { |
| 330 | return &Impl::emplace_back(std::forward<Args>(args)...); |
| 331 | } |
| 332 | |
| 333 | bool push_back(const value_type& v) { |
| 334 | Impl::push_back(v); |
| 335 | return true; |
| 336 | } |
| 337 | |
| 338 | bool push_back(value_type&& v) { |
| 339 | Impl::push_back(std::move(v)); |
| 340 | return true; |
| 341 | } |
| 342 | |
| 343 | using Impl::pop_back; |
| 344 | |
| 345 | void unstable_erase(iterator it) { |
| 346 | if (it != last()) std::iter_swap(it, last()); |
| 347 | pop_back(); |
| 348 | } |
| 349 | |
| 350 | void swap(SmallVector& other) { Impl::swap(other); } |
| 351 | }; |
| 352 | |
| 353 | template <typename> |
| 354 | struct IsSmallVector : std::false_type {}; |
| 355 | |
| 356 | template <typename T, size_t N> |
| 357 | struct IsSmallVector<SmallVector<T, N>> : std::true_type {}; |
| 358 | |
| 359 | // Deduction guide for array constructor. |
| 360 | template <typename T, size_t N> |
| 361 | SmallVector(T (&)[N]) -> SmallVector<std::remove_cv_t<T>, N>; |
| 362 | |
| 363 | // Deduction guide for variadic constructor. |
| 364 | template <typename T, typename... Us, typename V = std::decay_t<T>, |
| 365 | typename = std::enable_if_t<(std::is_constructible_v<V, Us> && ...)>> |
| 366 | SmallVector(T&&, Us&&...) -> SmallVector<V, 1 + sizeof...(Us)>; |
| 367 | |
| 368 | // Deduction guide for in-place constructor. |
| 369 | template <typename T, typename... Us> |
| 370 | SmallVector(std::in_place_type_t<T>, Us&&...) -> SmallVector<T, sizeof...(Us)>; |
| 371 | |
| 372 | // Deduction guide for StaticVector conversion. |
| 373 | template <typename T, size_t N> |
| 374 | SmallVector(StaticVector<T, N>&&) -> SmallVector<T, N>; |
| 375 | |
| 376 | template <typename T, size_t N> |
| 377 | inline void swap(SmallVector<T, N>& lhs, SmallVector<T, N>& rhs) { |
| 378 | lhs.swap(rhs); |
| 379 | } |
| 380 | |
| 381 | } // namespace android::ftl |