PX4-Autopilot/src/modules/sensors/vehicle_optical_flow/RingBuffer.hpp

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/**
 * @file RingBuffer.hpp
 * Template RingBuffer
 */

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

template <typename T, size_t SIZE>
class RingBuffer
{
public:
	void push(const T &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; }

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

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

	uint8_t get_oldest_index() const { return _tail; }

	bool peak_first_older_than(const uint64_t &timestamp, T *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)100'000) {
				*sample = _buffer[index];
				return true;
			}

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

		return false;
	}

	bool pop_first_older_than(const uint64_t &timestamp, T *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)100'000) {
				*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;
	}

	bool pop_oldest(const uint64_t &timestamp_oldest, const uint64_t &timestamp_newest, T *sample)
	{
		if (timestamp_oldest >= timestamp_newest) {
			return false;
		}

		for (uint8_t i = 0; i < SIZE; i++) {

			uint8_t index = (_tail + i) % SIZE;

			if (_buffer[index].time_us >= timestamp_oldest && _buffer[index].time_us <= timestamp_newest) {
				*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] = {};

				return true;
			}
		}

		return false;
	}

	bool pop_oldest(T *sample)
	{
		if (_tail == _head) {
			return false;
		}

		*sample = _buffer[_tail];
		_buffer[_tail].time_us = 0;

		_tail = (_tail + 1) % SIZE;

		return true;
	}

	bool pop_newest(T *sample)
	{
		if (_tail == _head) {
			return false;
		}

		*sample = _buffer[_head];
		_buffer[_head].time_us = 0;

		_head = (_head - 1) % SIZE;

		return true;
	}

	int get_total_size() const { return sizeof(*this) + sizeof(T) * SIZE; }

	uint8_t entries() const
	{
		int count = 0;

		for (uint8_t i = 0; i < SIZE; i++) {
			if (_buffer[i].time_us != 0) {
				count++;
			}
		}

		return count;
	}

private:
	T _buffer[SIZE] {};

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

	bool _first_write{true};
};