73 lines
1.5 KiB
C++
73 lines
1.5 KiB
C++
// SPDX-License-Identifier: BSD-2-Clause
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// author: Max Kellermann <max.kellermann@gmail.com>
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#ifndef REUSABLE_ARRAY_HXX
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#define REUSABLE_ARRAY_HXX
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#include <cstddef>
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#include <utility>
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/**
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* Manager for a temporary array which grows as needed. This attempts
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* to reduce the number of consecutive heap allocations and
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* deallocations.
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*
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* @param T the array element type
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* @param M always allocate multiples of this number; must be a power of 2
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*/
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template<typename T, size_t M=1>
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class ReusableArray {
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T *buffer = nullptr;
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size_t capacity = 0;
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public:
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ReusableArray() = default;
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ReusableArray(ReusableArray &&src)
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:buffer(std::exchange(src.buffer, nullptr)),
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capacity(std::exchange(src.capacity, 0)) {}
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ReusableArray &operator=(ReusableArray &&src) {
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std::swap(buffer, src.buffer);
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std::swap(capacity, src.capacity);
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return *this;
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}
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~ReusableArray() {
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delete[] buffer;
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}
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size_t GetCapacity() const {
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return capacity;
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}
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/**
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* Free resources allocated by this object. This invalidates
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* the buffer returned by Get().
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*/
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void Clear() {
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delete[] buffer;
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buffer = nullptr;
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capacity = 0;
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}
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/**
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* Get the buffer, and guarantee a minimum size. This buffer
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* becomes invalid with the next Get() call.
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*/
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[[gnu::malloc]] [[gnu::returns_nonnull]]
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T *Get(size_t size) {
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if (size > capacity) [[unlikely]] {
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/* too small: grow */
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delete[] buffer;
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capacity = ((size - 1) | (M - 1)) + 1;
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buffer = new T[capacity];
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}
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return buffer;
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}
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};
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#endif
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