/**************************************************************************
*
* ROUTINE
*               zerofilt_S
*
* FUNCTION
*               Direct form all-zero filter
*
* SYNOPSIS
*               subroutine zerofilt_S(b, n, z, xy, len)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       b               real    i       N+1 filter coefficients
*       n               int     i       Filter order
*       z               real    i/o     N+1 filter delay elements
*                                       (maintained by the user)
*       xy              real    i/o     Input/Output data array
*       len             int     i       Number of samples to filter
*
***************************************************************************/

zerofilt_S(a, n, z, xy, len)
int n, len;
float a[], z[], xy[];
{
  register float ar;
  register int t, j;

  for (t = 0; t < len; t++)
  {
    z[0] = xy[t];
    ar = 0.0;
    for (j = n; j > 0; j--) ar += a[j] * z[j];
    memmove( (char *)(z+1), (char *)(z), n*sizeof(float) );
    xy[t] = ar + a[0]*z[0];
  }

}