/*****************************************************************
**
** file: fir_filter.h
** Description:  Subroutines to implement a (real) FIR Filter in real-time.
**	         Multiple subroutine calls are used to calculate the output
**               of an FIR filter
**	             y(n) = x(n) * h(n)
**	         where x(n) is the nth input sample, and the values of h(n) 
**	         obtained from an array of fixed values, and "*" denotes 
**               discrete-time convolution.
**
** Implementation:
**   Filters are implemented using three function calls:
**     init_fir()   is called once, and is used to initialize the array
**                  of filter coefficients h(n), allocate any required memory,
**		    and perform any other required initialization.
**     calc_fir()   is called multiple times -- once for every input sample.
**                  It returns the filter output sample y(n).
**     destroy_fir() is called once at the end of the program, and is used
**                  to de-allocate any memory.
**
**  Function Prototypes and parameters:
**
**    	#include "fir_filter.h"
**	FIR_PARMS *init_fir(double *filter_coefs, int n_coef);
**
**	   Inputs:
**		filter_coefs	pointer to the array of values for h(n)
**        			filter_coefs[i] should contain the impulse
**				response of the filter at time "i", for 
**				i=0, 1, 2, ..., n_coef-1
**				The filter_coefs array is NOT modified by
**				init_fir(), calc_fir(), or destroy_fir().
**		n_coef  	Number of samples in the array
**	   Returned:
**		The function returns a pointer to a "FIR_PARMS" data type
**		(which is defined in "fir_filter.h")
**		
**	double calc_fir( FIR_PARMS *s, double x );
**
**	   Inputs:
**		s	pointer to FIR_PARMS, as provided by init_fir()
**		x	Input sample value
**	   Returned:
**		The function returns the FIR filter output sample y(n).
**
**                      i=n_coef-1
**		y(n) =    sum     ( h[i] x(n-i) )
**			  i=0
**
**		where x(n) is the value of "x" for the current call, x(n-1)
**		is the value of "x" from the previous call, x(n-2) is the 
**		value of "x" from call before that, and so on.  
**		
**  	void destroy_fir(FIR_PARMS *s);   
**  	   Inputs:
**	   	s	pointer to FIR_PARMS, as provided by init_fir()
**	   No value is returned.
** 
*******************************************************************/ 

#ifndef ECE486_FIR_FILTER
#define ECE486_FIR_FILTER

 /*******  ECE486 STUDENTS MODIFY THIS *******/

#endif