dvfir2.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:  dvfir2.c
 * DATE:  Nov 1, 1989
 * RELATED FILES:  
 * AUTHOR:  Mark Schrank
 * DESCRIPTION:  "c" Dvfir2 function
 * NOTES/WARNINGS:  
 * REVISION HISTORY:
 *	Release		Who	Date	Comments
 *      2.6    John Lundell 02/23/90  Changed Macro calls to register pointers.
 *      3.0    John Lundell 03/19/93  Collapsed two loops to one for efficiency.
 */
#include "cgs.h"
/*
 *---------------------------------------------------------------
 * FUNCTION:  Dvfir2(d_input,sp_state,sp_coef)
 * DESCRIPTION:  
 *	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 tapped-delay line.
 *	The entire vector is shifted with each new point.  Though
 *	this may seem slow, it is faster than Dvfir for short
 *	filter lengths.
 *
 * REVISION HISTORY:
 *	Release		Who	Date	Comments
 *      2.6    John Lundell 02/23/90  Changed Macro calls to register pointers.
 *      3.0    John Lundell 03/19/93  Collapsed two loops to one for efficiency.
 */

double Dvfir2(d_input, sp_state, sp_coef)
double 	d_input;
Ovector sp_state, sp_coef;
{
	register long 	n = sp_coef->length;
	register char  	*sp = sp_state->virtstart;
	register char	*cp = sp_coef->virtstart;
	register long	stps = sp_state->stepsize;
	register long	stpc = sp_coef->stepsize;
	register double	result = 0.0;
	register double	t2, t1 = d_input;
/*
 *  Calculate the output
 */
	while (n-- > 0) {
		result += *(double *) cp * t1;
		t2 = *(double *) sp;
		*(double *) sp = t1;
		t1 = t2;
		cp += stpc;
		sp += stps;
	} 

	return result;
}