px4_autopilot/EKF/RingBuffer.h

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/**
 * @file RingBuffer.h
 * @author Roman Bapst <bapstroman@gmail.com>
 * Template RingBuffer.
 */

#include <inttypes.h>
#include <cstdio>
#include <cstring>

template <typename data_type>
class RingBuffer
{
public:
	RingBuffer() = default;
	~RingBuffer() { delete[] _buffer; }

	// no copy, assignment, move, move assignment
	RingBuffer(const RingBuffer &) = delete;
	RingBuffer &operator=(const RingBuffer &) = delete;
	RingBuffer(RingBuffer &&) = delete;
	RingBuffer &operator=(RingBuffer &&) = delete;

	bool allocate(uint8_t size)
	{
		if (_buffer != nullptr) {
			delete[] _buffer;
		}

		_buffer = new data_type[size];

		if (_buffer == nullptr) {
			return false;
		}

		_size = size;

		_head = 0;
		_tail = 0;

		// set the time elements to zero so that bad data is not retrieved from the buffers
		for (unsigned index = 0; index < _size; index++) {
			_buffer[index].time_us = 0;
		}
		_first_write = true;

		return true;
	}

	void unallocate() {
		delete[] _buffer;
		_buffer = nullptr;
	}

	void push(const data_type& sample)
	{
		uint8_t head_new = _head;

		if (!_first_write) {
			head_new = (_head + 1) % _size;
		}

		_buffer[head_new] = sample;
		_head = head_new;

		// move tail if we overwrite it
		if (_head == _tail && !_first_write) {
			_tail = (_tail + 1) % _size;

		} else {
			_first_write = false;
		}
	}

	uint8_t get_length() const { return _size; }

	data_type &operator[](const uint8_t index) { return _buffer[index]; }

	const data_type& get_newest() { return _buffer[_head]; }
	const data_type& get_oldest() { return _buffer[_tail]; }

	uint8_t get_oldest_index() const { return _tail; }

	bool pop_first_older_than(const uint64_t& timestamp, data_type *sample)
	{
		// start looking from newest observation data
		for (uint8_t i = 0; i < _size; i++) {
			int index = (_head - i);
			index = index < 0 ? _size + index : index;

			if (timestamp >= _buffer[index].time_us && timestamp - _buffer[index].time_us < (uint64_t)1e5) {

				*sample = _buffer[index];

				// Now we can set the tail to the item which comes after the one we removed
				// since we don't want to have any older data in the buffer
				if (index == _head) {
					_tail = _head;
					_first_write = true;

				} else {
					_tail = (index + 1) % _size;
				}

				_buffer[index].time_us = 0;

				return true;
			}

			if (index == _tail) {
				// we have reached the tail and haven't got a match
				return false;
			}
		}

		return false;
	}



	// return ttrue if allocated
	unsigned is_allocated()
	{
		return (_buffer != NULL);
	}
private:
	data_type *_buffer{nullptr};

	uint8_t _head{0};
	uint8_t _tail{0};
	uint8_t _size{0};

	bool _first_write{true};
};