CircularBuffer.h

/*
Modified from https://en.wikipedia.org/wiki/Circular_buffer
Mirroring version
On 18 April 2014, the simplified version on the Wikipedia page for power of 2 sized buffers 
doesn't work - cbIsEmpty() returns true whether the buffer is full or empty.
*/

/** Circular buffer object.  Has a fixed number of cells, set to 256.
@tparam ITEM_TYPE the kind of data to store, eg. int, int8_t etc.
*/
template <class ITEM_TYPE>
class CircularBuffer
{

public:
    /** Constructor
    */
    CircularBuffer(): start(0),end(0),s_msb(0),e_msb(0)
    {
    }

    inline
    bool isFull() {
        return end == start && e_msb != s_msb;
    }

    inline
    bool isEmpty() {
        return end == start && e_msb == s_msb;
    }

    inline
    void write(ITEM_TYPE in) {
        items[end] = in;
        //if (isFull()) cbIncrStart(); /* full, overwrite moves start pointer */
        cbIncrEnd();
    }

    inline
    ITEM_TYPE read() {
        ITEM_TYPE out = items[start];
        cbIncrStart();
        return out;
    }

    inline
    unsigned long count() {
        return (num_buffers_read << 8) + start;
    }

private:
    ITEM_TYPE items[256];
    uint8_t         start;  /* index of oldest itement              */
    uint8_t         end;    /* index at which to write new itement  */
    uint8_t         s_msb;
    uint8_t         e_msb;
    unsigned long num_buffers_read;


    inline
    void cbIncrStart() {
        start++;
        if (start == 0) {
            s_msb ^= 1;
            num_buffers_read++;
        }
    }

    inline
    void cbIncrEnd() {
        end++;
        if (end == 0) e_msb ^= 1;
    }

};