Delay Line in C

C Code:

    static double D[M]; /* initialized to zero */
    static long ptr=0;  /* read-write offset */

    double delayline(double x)
    {
      double y = D[ptr]; /* read operation */
      D[ptr++] = x;      /* write operation */
      if (ptr >= M) { ptr -= M; } /* wrap ptr */
      return y;
    }

• Circular buffer in software
• Shared read/write pointer
• Length not easily modified in real time
• Internal state (``instance variables'')
  = length $M$ array + read pointer