circular_buffer.h

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/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          http://www.mrpt.org/                          |
   |                                                                        |
   | Copyright (c) 2005-2018, Individual contributors, see AUTHORS file     |
   | See: http://www.mrpt.org/Authors - All rights reserved.                |
   | Released under BSD License. See details in http://www.mrpt.org/License |
   +------------------------------------------------------------------------+ */
#ifndef circular_buffer_H
#define circular_buffer_H

#include <vector>
#include <stdexcept>

namespace mrpt::containers
{
/** A circular buffer of fixed size (defined at construction-time), implemented
 * with a std::vector as the underlying storage.
 * \note Defined in #include <mrpt/containers/circular_buffer.h>
 * \ingroup mrpt_containers_grp
 */
template <typename T>
class circular_buffer
{
   private:
    std::vector<T> m_data;
    /** not "const" to allow copy/move = ops. */
    size_t m_size;
    size_t m_next_read, m_next_write;

   public:
    circular_buffer(const size_t size)
        : m_data(size), m_size(size), m_next_read(0), m_next_write(0)
    {
        if (m_size <= 2) throw std::invalid_argument("size must be >2");
    }

    /** Insert a copy of the given element in the buffer.
      * \exception std::out_of_range If the buffer run out of space.
      */
    void push(T d)
    {
        auto new_idx = m_next_write + 1;
        if (new_idx == m_size) new_idx = 0;
        if (new_idx == m_next_read)
            throw std::out_of_range("push: circular_buffer is full");
        m_data[m_next_write] = d;
        m_next_write = new_idx;
    }

    /** Insert a reference of the given element in the buffer.
      * \exception std::out_of_range If the buffer run out of space.
      */
    void push_ref(const T& d)
    {
        m_data[m_next_write++] = d;
        if (m_next_write == m_size) m_next_write = 0;

        if (m_next_write == m_next_read)
            throw std::out_of_range("push: circular_buffer is full");
    }

    /** Insert an array of elements in the buffer.
      * \exception std::out_of_range If the buffer run out of space.
      */
    void push_many(T* array_elements, size_t count)
    {
        while (count--) push(*array_elements++);
    }

    /** Retrieve an element from the buffer.
      * \exception std::out_of_range If the buffer is empty.
      */
    T pop()
    {
        if (m_next_read == m_next_write)
            throw std::out_of_range("pop: circular_buffer is empty");

        const size_t i = m_next_read++;
        if (m_next_read == m_size) m_next_read = 0;
        return m_data[i];
    }

    /** Retrieve an element from the buffer.
      * \exception std::out_of_range If the buffer is empty.
      */
    void pop(T& out_val)
    {
        if (m_next_read == m_next_write)
            throw std::out_of_range("pop: circular_buffer is empty");

        out_val = m_data[m_next_read++];
        if (m_next_read == m_size) m_next_read = 0;
    }

    /** Pop a number of elements into a user-provided array.
      * \exception std::out_of_range If the buffer has less elements than
     * requested. */
    void pop_many(T* out_array, size_t count)
    {
        while (count--) pop(*out_array++);
    }

    /** Peek (see without modifying) what is to be read from the buffer if pop()
     * was to be called.
      * \exception std::out_of_range If the buffer is empty. */
    T peek() const
    {
        if (m_next_read == m_next_write)
            throw std::out_of_range("peek: circular_buffer is empty");
        return m_data[m_next_read];
    }
    /** Like peek(), but seeking ahead in the buffer (index=0 means the
     * immediate next element, index=1 the following one, etc.)
      * \exception std::out_of_range If trying to read passing the number of
     * available elements. */
    T peek(size_t index) const
    {
        if (index >= this->size())
            throw std::out_of_range("peek: seek out of range");
        return m_data[(m_next_read + index) % m_size];
    }

    /** Like peek(), for multiple elements, storing a number of elements into a
     * user-provided array.
      * \exception std::out_of_range If the buffer has less elements than
     * requested. */
    void peek_many(T* out_array, size_t count) const
    {
        size_t peek_read = m_next_read;
        while (count--)
        {
            if (peek_read == m_next_write)
                throw std::out_of_range("peek: circular_buffer is empty");
            T val = m_data[peek_read++];
            if (peek_read == m_size) peek_read = 0;
            *out_array++ = val;
        }
    }

    /** Return the number of elements available for read ("pop") in the buffer
     * (this is NOT the maximum size of the internal buffer)
      * \sa capacity */
    size_t size() const
    {
        if (m_next_write >= m_next_read)
            return m_next_write - m_next_read;
        else
            return m_next_write + (m_size - m_next_read);
    }

    /** Return the maximum capacity of the buffer.
      * \sa size
      */
    size_t capacity() const { return m_size; }
    /** The maximum number of elements that can be written ("push") without
     * rising an overflow error.
      */
    size_t available() const { return (capacity() - size()) - 1; }
    /** Delete all the stored data, if any. */
    void clear() { m_next_write = m_next_read = 0; }
};  // end class circular_buffer

}
#endif