dvfir.c

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/*
 *	*************************************************************************
 *	*									*
 *	*	This confidential and proprietary software may be used only	*
 *	*  as authorized by a licensing agreement from the Alta Group of	*
 *	*  Cadence Design Systems, Inc.  In the event of publication, the	*
 *	*  following notice is applicable:					*
 *	*									*
 *	*    (c) COPYRIGHT 1995 ALTA GROUP OF CADENCE DESIGN SYSTEMS, INC.	*
 *	*			ALL RIGHTS RESERVED				*
 *	*									*
 *	*	The entire notice above must be reproduced on all authorized	*
 *	*  copies.								*
 *	*									*
 *	*************************************************************************
 *
 */
/*
 * FILE:  dvfir.c
 * DATE:  Nov 1, 1989
 * RELATED FILES:  
 * AUTHOR:  Mark Schrank
 * DESCRIPTION:  "c" Dvfir function
 * NOTES/WARNINGS:  
 * REVISION HISTORY:
 *	Release		Who	Date	Comments
 *      2.6    John Lundell 02/23/90  Changed Macro calls to register pointers.
 */
#include "cgs.h"
/*
 *---------------------------------------------------------------
 * FUNCTION:  Dvfir(d_input,sp_state,sp_coef)
 * DESCRIPTION:  
 *	double Dvfir(double input, Ovector *state, Ovector *coef);
 *
 *	Performs a single FIR filter output using passed filter
 *	input, state, and coefficients
 *
 * RETURN VALUE:  The filter output
 * NOTES/WARNINGS: 
 *	This function uses the state vector as a circular buffer.
 *	The dot product is therefore split into two parts.  The
 *	first part performs the dot product from the current location
 *	to the end of the state vector.  The second part is the dot
 *	product from the state vector start to the until the end of
 *	filter.
 *	
 *	This function only uses the points in the state vector in the
 *	set [state->virtstart, state->virtend).  The number of points
 *	in this set must be >= the length of the coef vector.  This
 *	function ignores the step size of the state vector and assumes
 *	that the curr_loc is not changed from call to call.
 *
 * REVISION HISTORY:
 *	Release		Who	Date	Comments
 *      2.6    John Lundell 02/23/90  Changed Macro calls to register pointers.
 */

double Dvfir(d_input, sp_state, sp_coef)
double d_input;
Ovector sp_state;
Ovector sp_coef;
{
	register long 	n = sp_coef->length;
	register double	*sp = (double *) sp_state->curr_loc;
	register double *se = (double *) sp_state->virtend;
	register char	*cp = sp_coef->virtstart;
	register long	stpc = sp_coef->stepsize;
	register double	result = 0.0;

/*
 *  Update the circular buffer pointer.
 */
	if (sp-- <= (double *) sp_state->virtstart) {
		sp = se - 1;
	}
	*sp = d_input;
	sp_state->curr_loc = (char *) sp;
/*
 *  Get the output
 */
	while (n-- > 0) {
		result += *sp++ * *(double *) cp;
		cp += stpc;
		if (sp >= se) sp = (double *) sp_state->virtstart;
	}

	return result;
}