diff --git a/src/Makefile.am b/src/Makefile.am index ad37928b4d..87bb2b945c 100644 --- a/src/Makefile.am +++ b/src/Makefile.am @@ -333,6 +333,7 @@ BITCOIN_CORE_H = \ util/translation.h \ util/types.h \ util/ui_change_type.h \ + util/vecdeque.h \ util/vector.h \ validation.h \ validationinterface.h \ diff --git a/src/util/vecdeque.h b/src/util/vecdeque.h new file mode 100644 index 0000000000..b5e7278473 --- /dev/null +++ b/src/util/vecdeque.h @@ -0,0 +1,316 @@ +// Copyright (c) The Bitcoin Core developers +// Distributed under the MIT software license, see the accompanying +// file COPYING or http://www.opensource.org/licenses/mit-license.php. + +#ifndef BITCOIN_UTIL_VECDEQUE_H +#define BITCOIN_UTIL_VECDEQUE_H + +#include + +#include +#include + +/** Data structure largely mimicking std::deque, but using single preallocated ring buffer. + * + * - More efficient and better memory locality than std::deque. + * - Most operations ({push_,pop_,emplace_,}{front,back}(), operator[], ...) are O(1), + * unless reallocation is needed (in which case they are O(n)). + * - Supports reserve(), capacity(), shrink_to_fit() like vectors. + * - No iterator support. + * - Data is not stored in a single contiguous block, so no data(). + */ +template +class VecDeque +{ + /** Pointer to allocated memory. Can contain constructed and uninitialized T objects. */ + T* m_buffer{nullptr}; + /** m_buffer + m_offset points to first object in queue. m_offset = 0 if m_capacity is 0; + * otherwise 0 <= m_offset < m_capacity. */ + size_t m_offset{0}; + /** Number of objects in the container. 0 <= m_size <= m_capacity. */ + size_t m_size{0}; + /** The size of m_buffer, expressed as a multiple of the size of T. */ + size_t m_capacity{0}; + + /** Returns the number of populated objects between m_offset and the end of the buffer. */ + size_t FirstPart() const noexcept { return std::min(m_capacity - m_offset, m_size); } + + void Reallocate(size_t capacity) + { + Assume(capacity >= m_size); + Assume((m_offset == 0 && m_capacity == 0) || m_offset < m_capacity); + // Allocate new buffer. + T* new_buffer = capacity ? std::allocator().allocate(capacity) : nullptr; + if (capacity) { + if constexpr (std::is_trivially_copyable_v) { + // When T is trivially copyable, just copy the data over from old to new buffer. + size_t first_part = FirstPart(); + if (first_part != 0) { + std::memcpy(new_buffer, m_buffer + m_offset, first_part * sizeof(T)); + } + if (first_part != m_size) { + std::memcpy(new_buffer + first_part, m_buffer, (m_size - first_part) * sizeof(T)); + } + } else { + // Otherwise move-construct in place in the new buffer, and destroy old buffer objects. + size_t old_pos = m_offset; + for (size_t new_pos = 0; new_pos < m_size; ++new_pos) { + std::construct_at(new_buffer + new_pos, std::move(*(m_buffer + old_pos))); + std::destroy_at(m_buffer + old_pos); + ++old_pos; + if (old_pos == m_capacity) old_pos = 0; + } + } + } + // Deallocate old buffer and update housekeeping. + std::allocator().deallocate(m_buffer, m_capacity); + m_buffer = new_buffer; + m_offset = 0; + m_capacity = capacity; + Assume((m_offset == 0 && m_capacity == 0) || m_offset < m_capacity); + } + + /** What index in the buffer does logical entry number pos have? */ + size_t BufferIndex(size_t pos) const noexcept + { + Assume(pos < m_capacity); + // The expression below is used instead of the more obvious (pos + m_offset >= m_capacity), + // because the addition there could in theory overflow with very large deques. + if (pos >= m_capacity - m_offset) { + return (m_offset + pos) - m_capacity; + } else { + return m_offset + pos; + } + } + + /** Specialization of resize() that can only shrink. Separate so that clear() can call it + * without requiring a default T constructor. */ + void ResizeDown(size_t size) noexcept + { + Assume(size <= m_size); + if constexpr (std::is_trivially_destructible_v) { + // If T is trivially destructible, we do not need to do anything but update the + // housekeeping record. Default constructor or zero-filling will be used when + // the space is reused. + m_size = size; + } else { + // If not, we need to invoke the destructor for every element separately. + while (m_size > size) { + std::destroy_at(m_buffer + BufferIndex(m_size - 1)); + --m_size; + } + } + } + +public: + VecDeque() noexcept = default; + + /** Resize the deque to be exactly size size (adding default-constructed elements if needed). */ + void resize(size_t size) + { + if (size < m_size) { + // Delegate to ResizeDown when shrinking. + ResizeDown(size); + } else if (size > m_size) { + // When growing, first see if we need to allocate more space. + if (size > m_capacity) Reallocate(size); + while (m_size < size) { + std::construct_at(m_buffer + BufferIndex(m_size)); + ++m_size; + } + } + } + + /** Resize the deque to be size 0. The capacity will remain unchanged. */ + void clear() noexcept { ResizeDown(0); } + + /** Destroy a deque. */ + ~VecDeque() + { + clear(); + Reallocate(0); + } + + /** Copy-assign a deque. */ + VecDeque& operator=(const VecDeque& other) + { + if (&other == this) [[unlikely]] return *this; + clear(); + Reallocate(other.m_size); + if constexpr (std::is_trivially_copyable_v) { + size_t first_part = other.FirstPart(); + Assume(first_part > 0 || m_size == 0); + if (first_part != 0) { + std::memcpy(m_buffer, other.m_buffer + other.m_offset, first_part * sizeof(T)); + } + if (first_part != other.m_size) { + std::memcpy(m_buffer + first_part, other.m_buffer, (other.m_size - first_part) * sizeof(T)); + } + m_size = other.m_size; + } else { + while (m_size < other.m_size) { + std::construct_at(m_buffer + BufferIndex(m_size), other[m_size]); + ++m_size; + } + } + return *this; + } + + /** Swap two deques. */ + void swap(VecDeque& other) noexcept + { + std::swap(m_buffer, other.m_buffer); + std::swap(m_offset, other.m_offset); + std::swap(m_size, other.m_size); + std::swap(m_capacity, other.m_capacity); + } + + /** Non-member version of swap. */ + friend void swap(VecDeque& a, VecDeque& b) noexcept { a.swap(b); } + + /** Move-assign a deque. */ + VecDeque& operator=(VecDeque&& other) noexcept + { + swap(other); + return *this; + } + + /** Copy-construct a deque. */ + VecDeque(const VecDeque& other) { *this = other; } + /** Move-construct a deque. */ + VecDeque(VecDeque&& other) noexcept { swap(other); } + + /** Equality comparison between two deques (only compares size+contents, not capacity). */ + bool friend operator==(const VecDeque& a, const VecDeque& b) + { + if (a.m_size != b.m_size) return false; + for (size_t i = 0; i < a.m_size; ++i) { + if (a[i] != b[i]) return false; + } + return true; + } + + /** Comparison between two deques, implementing lexicographic ordering on the contents. */ + std::strong_ordering friend operator<=>(const VecDeque& a, const VecDeque& b) + { + size_t pos_a{0}, pos_b{0}; + while (pos_a < a.m_size && pos_b < b.m_size) { + auto cmp = a[pos_a++] <=> b[pos_b++]; + if (cmp != 0) return cmp; + } + return a.m_size <=> b.m_size; + } + + /** Increase the capacity to capacity. Capacity will not shrink. */ + void reserve(size_t capacity) + { + if (capacity > m_capacity) Reallocate(capacity); + } + + /** Make the capacity equal to the size. The contents does not change. */ + void shrink_to_fit() + { + if (m_capacity > m_size) Reallocate(m_size); + } + + /** Construct a new element at the end of the deque. */ + template + void emplace_back(Args&&... args) + { + if (m_size == m_capacity) Reallocate((m_size + 1) * 2); + std::construct_at(m_buffer + BufferIndex(m_size), std::forward(args)...); + ++m_size; + } + + /** Move-construct a new element at the end of the deque. */ + void push_back(T&& elem) { emplace_back(std::move(elem)); } + + /** Copy-construct a new element at the end of the deque. */ + void push_back(const T& elem) { emplace_back(elem); } + + /** Construct a new element at the beginning of the deque. */ + template + void emplace_front(Args&&... args) + { + if (m_size == m_capacity) Reallocate((m_size + 1) * 2); + std::construct_at(m_buffer + BufferIndex(m_capacity - 1), std::forward(args)...); + if (m_offset == 0) m_offset = m_capacity; + --m_offset; + ++m_size; + } + + /** Copy-construct a new element at the beginning of the deque. */ + void push_front(const T& elem) { emplace_front(elem); } + + /** Move-construct a new element at the beginning of the deque. */ + void push_front(T&& elem) { emplace_front(std::move(elem)); } + + /** Remove the first element of the deque. Requires !empty(). */ + void pop_front() + { + Assume(m_size); + std::destroy_at(m_buffer + m_offset); + --m_size; + ++m_offset; + if (m_offset == m_capacity) m_offset = 0; + } + + /** Remove the last element of the deque. Requires !empty(). */ + void pop_back() + { + Assume(m_size); + std::destroy_at(m_buffer + BufferIndex(m_size - 1)); + --m_size; + } + + /** Get a mutable reference to the first element of the deque. Requires !empty(). */ + T& front() noexcept + { + Assume(m_size); + return m_buffer[m_offset]; + } + + /** Get a const reference to the first element of the deque. Requires !empty(). */ + const T& front() const noexcept + { + Assume(m_size); + return m_buffer[m_offset]; + } + + /** Get a mutable reference to the last element of the deque. Requires !empty(). */ + T& back() noexcept + { + Assume(m_size); + return m_buffer[BufferIndex(m_size - 1)]; + } + + /** Get a const reference to the last element of the deque. Requires !empty(). */ + const T& back() const noexcept + { + Assume(m_size); + return m_buffer[BufferIndex(m_size - 1)]; + } + + /** Get a mutable reference to the element in the deque at the given index. Requires idx < size(). */ + T& operator[](size_t idx) noexcept + { + Assume(idx < m_size); + return m_buffer[BufferIndex(idx)]; + } + + /** Get a const reference to the element in the deque at the given index. Requires idx < size(). */ + const T& operator[](size_t idx) const noexcept + { + Assume(idx < m_size); + return m_buffer[BufferIndex(idx)]; + } + + /** Test whether the contents of this deque is empty. */ + bool empty() const noexcept { return m_size == 0; } + /** Get the number of elements in this deque. */ + size_t size() const noexcept { return m_size; } + /** Get the capacity of this deque (maximum size it can have without reallocating). */ + size_t capacity() const noexcept { return m_capacity; } +}; + +#endif // BITCOIN_UTIL_VECDEQUE_H