CircularBuffer.h

/*
 * CircularBuffer.h
 *
 * This file is part of Mozzi.
 *
 * Copyright 2014-2024 Tim Barrass and the Mozzi Team
 *
 * Mozzi is licensed under the GNU Lesser General Public Licence (LGPL) Version 2.1 or later.
 *
 */
 
/*
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.
 
April 2025: modified for different buffer sizes under the suggestion
of Meebleeps (https://github.com/sensorium/Mozzi/issues/281)
*/
 
 
 
template <class ITEM_TYPE, int16_t BUFFER_SIZE>
class CircularBuffer
{
 
public:
    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 << COUNT_LSHIFT) + start;
    }
        inline
    ITEM_TYPE * address() {
      return items;
    }
 
private:
    ITEM_TYPE items[BUFFER_SIZE];
    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;
    static constexpr unsigned long COUNT_LSHIFT = 
        (BUFFER_SIZE == 256) ? 8 :
        (BUFFER_SIZE == 128) ? 7 :
        (BUFFER_SIZE == 64) ? 6 :
        (BUFFER_SIZE == 32) ? 5 :
        (BUFFER_SIZE == 16) ? 4 :
        (BUFFER_SIZE == 8) ? 3 :
        (BUFFER_SIZE == 4) ? 2 :
        (BUFFER_SIZE == 2) ? 1 : 0;
 
  inline
  void cbIncrStart()  {
    start++;
    if (start == BUFFER_SIZE)
      {
    start = 0;
    s_msb ^= 1;
    num_buffers_read++;
      }
  }
 
  inline
  void cbIncrEnd()
  {
    end++;
    if (end == BUFFER_SIZE)
      {
    end = 0;
    e_msb ^= 1;
      }
  }
  
 
};
 
 
 
template <class ITEM_TYPE>
class CircularBuffer<ITEM_TYPE, 256>
{
public:
    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;
    }
        inline
    ITEM_TYPE * address() {
      return items;
    }
 
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;
    }
};