fixed_vector.h

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/*  fixed_vector.h                                                        */
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#pragma once

#include "core/templates/span.h"

/**
 * A high performance Vector of fixed capacity.
 * Especially useful if you need to create an array on the stack, to
 *  prevent dynamic allocations (especially in bottleneck code).
 *
 * Choose CAPACITY such that it is enough for all elements that could be added through all branches.
 *
 */
template <class T, uint32_t CAPACITY>
class FixedVector {
	// This declaration allows us to access other FixedVector's private members.
	template <class T_, uint32_t CAPACITY_>
	friend class FixedVector;

	uint32_t _size = 0;
	alignas(T) uint8_t _data[CAPACITY * sizeof(T)];

	constexpr static uint32_t DATA_PADDING = MAX(alignof(T), alignof(uint32_t)) - alignof(uint32_t);

public:
	_FORCE_INLINE_ constexpr FixedVector() = default;
	constexpr FixedVector(std::initializer_list<T> p_init) {
		ERR_FAIL_COND(p_init.size() > CAPACITY);
		for (const T &element : p_init) {
			memnew_placement(ptr() + _size++, T(element));
		}
	}

	template <uint32_t p_capacity>
	constexpr FixedVector(const FixedVector<T, p_capacity> &p_from) {
		ERR_FAIL_COND(p_from.size() > CAPACITY);
		if constexpr (std::is_trivially_copyable_v<T>) {
			// Copy size and all provided elements at once.
			memcpy((void *)&_size, (void *)&p_from._size, sizeof(_size) + DATA_PADDING + p_from.size() * sizeof(T));
		} else {
			for (const T &element : p_from) {
				memnew_placement(ptr() + _size++, T(element));
			}
		}
	}

	template <uint32_t p_capacity>
	constexpr FixedVector(FixedVector<T, p_capacity> &&p_from) {
		ERR_FAIL_COND(p_from.size() > CAPACITY);
		// Copy size and all provided elements at once.
		// Note: Assumes trivial relocatability.
		memcpy((void *)&_size, (void *)&p_from._size, sizeof(_size) + DATA_PADDING + p_from.size() * sizeof(T));
		p_from._size = 0;
	}

	~FixedVector() {
		if constexpr (!std::is_trivially_destructible_v<T>) {
			for (uint32_t i = 0; i < _size; i++) {
				ptr()[i].~T();
			}
		}
	}

	_FORCE_INLINE_ constexpr T *ptr() { return (T *)(_data); }
	_FORCE_INLINE_ constexpr const T *ptr() const { return (const T *)(_data); }

	_FORCE_INLINE_ constexpr operator Span<T>() const { return Span<T>(ptr(), size()); }
	_FORCE_INLINE_ constexpr Span<T> span() const { return operator Span<T>(); }

	_FORCE_INLINE_ constexpr uint32_t size() const { return _size; }
	_FORCE_INLINE_ constexpr bool is_empty() const { return !_size; }
	_FORCE_INLINE_ constexpr bool is_full() const { return _size == CAPACITY; }
	_FORCE_INLINE_ constexpr uint32_t capacity() const { return CAPACITY; }

	_FORCE_INLINE_ constexpr void clear() { resize_initialized(0); }

	/// Changes the size of the vector.
	/// If p_size > size(), constructs new elements.
	/// If p_size < size(), destructs new elements.
	constexpr Error resize_initialized(uint32_t p_size) {
		if (p_size > _size) {
			ERR_FAIL_COND_V(p_size > CAPACITY, ERR_OUT_OF_MEMORY);
			memnew_arr_placement(ptr() + _size, p_size - _size);
		} else if (p_size < _size) {
			if constexpr (!std::is_trivially_destructible_v<T>) {
				for (uint32_t i = p_size; i < _size; i++) {
					ptr()[i].~T();
				}
			}
		}

		_size = p_size;
		return OK;
	}

	/// Changes the size of the vector.
	/// The initializer of new elements is skipped, making this function faster than resize_initialized.
	/// The caller is required to initialize the new values.
	constexpr Error resize_uninitialized(uint32_t p_size) {
		static_assert(std::is_trivially_destructible_v<T>, "resize_uninitialized is unsafe to call if T is not trivially destructible.");
		ERR_FAIL_COND_V(p_size > CAPACITY, ERR_OUT_OF_MEMORY);
		_size = p_size;
		return OK;
	}

	constexpr void push_back(const T &p_val) {
		ERR_FAIL_COND(_size >= CAPACITY);
		memnew_placement(ptr() + _size, T(p_val));
		_size++;
	}

	constexpr void pop_back() {
		ERR_FAIL_COND(_size == 0);
		_size--;
		ptr()[_size].~T();
	}

	// NOTE: Subscripts sanity check the bounds to avoid undefined behavior.
	//       This is slower than direct buffer access and can prevent autovectorization.
	//       If the bounds are known, use ptr() subscript instead.
	constexpr const T &operator[](uint32_t p_index) const {
		CRASH_COND(p_index >= _size);
		return ptr()[p_index];
	}

	constexpr T &operator[](uint32_t p_index) {
		CRASH_COND(p_index >= _size);
		return ptr()[p_index];
	}

	_FORCE_INLINE_ constexpr T *begin() { return ptr(); }
	_FORCE_INLINE_ constexpr T *end() { return ptr() + _size; }

	_FORCE_INLINE_ constexpr const T *begin() const { return ptr(); }
	_FORCE_INLINE_ constexpr const T *end() const { return ptr() + _size; }
};