/**************************************************************************
*
* ROUTINE
*               smoothtau
*
* FUNCTION
*
*               smooth tau values when two errors detected in Hamming block
*
* SYNOPSIS
*               smoothtau(tau,twoerror,syndavg,tau3,subframe)
*
*   formal
*
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       tau		float	i/o	input tau
*	twoerror	int	i	two error flag
*	syndavg		float	i	error rate estimation parameter
*	tau3		int	i	third tau value
*	subframe	int	i	subframe number
*
*   external
*                       data    I/O
*       name            type    type    function
*       -------------------------------------------------------------------
*       frame           int     i
*
***************************************************************************
*
* DESCRIPTION
*
*	Smoothing routine to smooth tau (pitch lag) when errors are detected:
*
*	If the variance of past tau values is within the range VARLIMIT
*	(indicating voiced speech) the validity of the current tau value
*	is tested.  If the current value of TAU is within the range TAULIMIT,
*	TAU is passed.  If TAU is not within that range TAULIMIT, TAU is reset 
*	to the average value of taus. 
*
*	The array OLDTAU contains past values of tau.  The array VECTOR
*	is constructed from the array OLDTAU and TAU3 for subframes 1
*	and 2 (TAU3 is a future absolute tau value).  For subframes 3
*	and 4 there are no valid future values (since delta taus in the 
*	future are not valid), therefore the array VECTOR is constructed 
*	entirely from the array OLDTAU.  Decisions concering smoothing of 
*	a particular tau are made on the variance of the array VECTOR and 
*	the tau in question (TAU).
*
*	If the value of tau is smoothed in subframe 3, smoothing is disabled
*	for subframe 4 of the same frame since the tau value in subframe 4
*	is a delta based on subframe 3.
*
*	Note:  The smoothing parameters should be capable of adapting
*	to various bit error rate estimates. For example, different
*	values of SYNDAVG should select different levels of TAULIMIT and
*	VARLIMIT.
*
***************************************************************************
*
* CALLED BY
*
*       celp
*
* CALLS
*
*
*
**************************************************************************/
#include <math.h>
#define TAUHISTORY	4
#define TAULIMIT	15
#define VARLIMIT	15
#define SYNDLIMIT       0.04
#define TRUE            1
#define FALSE           0
#define nint(F)          (((F)>0)?(int)(F+0.5):(int)(F-0.5))
extern int frame;
smoothtau(tau, twoerror, syndavg, tau3, subframe)
int twoerror, subframe;
float *tau, syndavg, tau3;
{
  int i;
  static int enable;
  float avg, var, vector[4];
  static float oldtau[TAUHISTORY];

  if (subframe != 4)
    enable = TRUE;
  if ((twoerror || syndavg > SYNDLIMIT) && enable)
  {
    if (subframe == 1)
    {
      vector[0] = oldtau[0];
      vector[1] = oldtau[1];
      vector[2] = oldtau[2];
      vector[3] = tau3;
    }
    else if (subframe == 2)
    {
      vector[0] = oldtau[0];
      vector[1] = oldtau[1];
      vector[2] = oldtau[2];
      vector[3] = tau3;
    }
    else if (subframe == 3)
    {
      vector[0] = oldtau[0];
      vector[1] = oldtau[1];
      vector[2] = oldtau[2];
      vector[3] = oldtau[3];
    }
    else if (subframe == 4)
    {
      vector[0] = oldtau[0];
      vector[1] = oldtau[1];
      vector[2] = oldtau[2];
      vector[3] = oldtau[3];
    }
    else
      printf("smoothtau: Error in subframe number\n");

    variance(vector, 4, &var, &avg);
    if (var < VARLIMIT && (*tau >= avg + TAULIMIT || *tau <= avg - TAULIMIT))
    {
      *tau = nint(avg);
      printf("smoothtau: tau value reset to avg at frame %d subframe %d\n",
	      frame, subframe);
      if (subframe == 3)
      {
	enable = FALSE;
	printf("smoothpgain: tau smoothing disabled for subframe 4\n");
      }
    }
  }

  for (i = TAUHISTORY - 1; i > 0; i--)
    oldtau[i] = oldtau[i - 1];
  oldtau[0] = *tau;
}