/*****************************************************************************
*                                                                            *
*   CIRCONV.SPL   Copyright (C) 2003 DSP Development Corporation             *
*                               All Rights Reserved                          *
*                                                                            *
*   Author:      Randy Race                                                  *
*                                                                            *
*   Synopsis:    Circular Convolution using CONV                             *
*                                                                            *
*   Revisions:    4 Apr 2003  RRR  Creation - from FCONV.SPL                 *
*                                                                            *
*****************************************************************************/

#if @HELP_CIRCONV

    CIRCONV

    Purpose: Circular convolution in the time domain

    Syntax:  CIRCONV(s1, s2, N)

                 s1 - input series

                 s2 - input series

                  N - Optional. An integer, the convolution length, defaults
                      to the maximum length of the input series.

    Returns: A series

    Example:
             W1: {1, 2, 3}
             W2: {4, 5, 6}
             W3: circonv(w1, w2)

             W3 contains the series {31, 31, 28} the result of circular
             convolution of W1 and W2.

    Remarks:
             CIRCONV performs convolution by extending one of the input
             series and using the time domain linear convolution function
             CONV.

             See FCIRCONV for a frequency domain implementation.


    See Also:
             Conv
             Fcirconv
             Fconv
#endif


/* time domain circular convolution */
circonv(s1, s2, N)
{
        local c;

        if (argc < 3)
        {
                if (argc < 2) error("circonv - two input series required");
                
                /* default to maximum length */
                N = max(length(s1), length(s2));
        }

        /* use offset and length options of conv */
        c = conv(rep(extract(s1, 1, N), 2), extract(s2, 1, N), N + 1, N);

        /* set xoffset */
        setxoffset(c, xoffset(s1) + xoffset(s2));

        return(c);
}