/*ADAPTSH.C - ADAPTIVE FILTER WITH SHIFTED INPUT   */
#include "math.h"
#define beta 0.005           /*rate of convergence */               
#define N  30                /*# of coefficients   */
#define NS 128               /*# of output samples */               
#define pi  3.1415926                     
#define shift 90          /*desired amount of shift*/ 
#define Fs 8000           /*sampling frequency     */
#define inp 1000*sin(2*pi*T*1000/Fs) /*input signal*/

main()
{
 int I, T;
 double xin, x, ys, D, E, Y1; 
 double W[N+1];
 double Delay[N+1];
 volatile int *IO_OUTPUT = (volatile int*) 0x809d00;
 ys = 0;
 for (T = 0; T < N; T++)
  {
   W[T] = 0.0;
   Delay[T] = 0.0;
  }                
 for (T=0; T < NS; T++) /*# of output samples          */       
  {  
   xin = inp/1000;      /*input between 1 and -1       */
   if (ys >= xin)       /*is signal rising or falling  */
    x = acos(xin);      /*signal is falling            */
   else                 /*otherwise                    */
    x=asin(xin)-(pi/2); /*signal is rising             */
   x = x - (shift);     /*shift                        */
   Delay[0]=cos(x);     /*shifted output=filter's input*/
   D = inp;             /*input data                   */
   Y1 = 0;              /*init output                  */
   ys = xin;            /*store input value            */ 
   for (I=0; I <N; I++) /*for N coefficients           */
    Y1+=W[I]*Delay[I];  /*adaptive filter output       */            
   E = D - Y1;          /*error signal                 */             
   for (I=N; I>0; I--)         
    {
     W[I]=W[I]+(beta*E*Delay[I]); /*update weights     */  
     if (I != 0)                     
     Delay[I] = Delay[I-1];       /*update delays      */       
    } 
   *IO_OUTPUT++ = Y1;             /*overall output     */
  }   
}