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()
	{
		_buffer = NULL;
		_head = _tail = _size = 0;
		_first_write = true;
	}
	~RingBuffer() { delete[] _buffer; }

	bool allocate(int size)
	{
		if (size <= 0) {
			return false;
		}

		if (_buffer != NULL) {
			delete[] _buffer;
		}

		_buffer = new data_type[size];

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

		_size = size;
		// 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()
	{
		if (_buffer != NULL) {
			delete[] _buffer;
		}
	}

	inline void push(data_type sample)
	{
		int head_new = _head;

		if (_first_write) {
			head_new = _head;

		} else {
			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;
		}
	}

	inline data_type get_oldest()
	{
		return _buffer[_tail];
	}

	inline data_type get_newest()
	{
		return _buffer[_head];
	}

	inline bool pop_first_older_than(uint64_t timestamp, data_type *sample)
	{
		// start looking from newest observation data
		for (unsigned 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 < 100000) {

				// TODO Re-evaluate the static cast and usage patterns
				memcpy(static_cast<void *>(sample), static_cast<void *>(&_buffer[index]), sizeof(*sample));

				// 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 == static_cast<int>(_head)) {
					_tail = _head;
					_first_write = true;

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

				_buffer[index].time_us = 0;

				return true;
			}

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

		return false;
	}

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

	// return data at the specified index
	inline data_type get_from_index(unsigned index)
	{
		if (index >= _size) {
			index = _size-1;
		}
		return _buffer[index];
	}

	// push data to the specified index
	inline void push_to_index(unsigned index, data_type sample)
	{
		if (index >= _size) {
			index = _size-1;
		}
		_buffer[index] = sample;
	}

	// return the length of the buffer
	unsigned get_length()
	{
		return _size;
	}

private:
	data_type *_buffer;
	unsigned _head, _tail, _size;
	bool _first_write;

	// debug
	uint64_t _time_last;
};