annotate wdf/fir.c @ 0:5242703e91d3 tip

Initial checkin for AIM92 aimR8.2 (last updated May 1997).

/*
    Copyright (c) Applied Psychology Unit, Medical Research Council. 1988, 1989
    ===========================================================================

    Permission to use, copy, modify, and distribute this software without fee 
    is hereby granted for research purposes, provided that this copyright 
    notice appears in all copies and in all supporting documentation, and that 
    the software is not redistributed for any fee (except for a nominal shipping 
    charge). Anyone wanting to incorporate all or part of this software in a
    commercial product must obtain a license from the Medical Research Council.

    The MRC makes no representations about the suitability of this 
    software for any purpose.  It is provided "as is" without express or implied 
    warranty.
 
    THE MRC DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING 
    ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL THE
    A.P.U. BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY 
    DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN 
    AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

/*  
    Acknowledgment:
    ==============

    The source code provided in this file was originally developed by 
    Christian Giguere as part of a Ph.D degree at the Department of
    Engineering of the University of Cambridge from April 1990 to
    November 1993. The code was subsequently adapted under a grant
    from the Hearing Research Trust for full compatibility with 
    AIM Release 6.15.

    Christian Giguere 25/03/94

*/

/*
    ===========================================================
    fir.c
    ===========================================================

    Finite Impulse Response (FIR) filtering module.
    
    Author        : Christian Giguere
    First written : 12th November, 1990
    Last edited   : 22nd September, 1991
    
    Reference:
    (1) A.V.Oppenheim and R.W.Schafer (1975). Digital Signal
        Processing (Prentice-Hall), Sections 4.5.5 and 5.5.
    ===========================================================
*/


/***** includes *****/

#include <math.h>
#include <stdio.h>
#include "stitch.h"
#include "calc.h"
#include "calc_tl.h"
#include "fir.h"


/***** defines *****/

#define NUMBER_OF_COEFFS     (               51 )                 /* odd order */
#define NUMBER_OF_STATES     ( NUMBER_OF_COEFFS ) 


/***** functions *****/

/*******************************************************************************
* name:                 function:  
*
* NewLpFIRfilter()      Design of LowPass FIR filter using windowing technique
*                       (Hamming window). It generates the multiplier coefficients
*                       and initializes the states of the filter. It returns a 
*                       pointer to a structure containing all relevant information 
*                       for the realisation of the filter.
*
* DoFIRfilter()         Direct form realisation for FIR filter of odd order linear
*                       phase. It is called by function ``upsample_callback()'' 
*                       in file ``upsample.c'' once for a specified number of input 
*                       points.  It computes the filter output for each input point
*                       and keeps track of the filter states. 
*
* CloseFIRfilter()      Deletes all private data structures and arrays of the FIR 
*                       filter upon comletion of filtering.  It is called by function
*                       ``upsample_callback()'' in file ``upsample.c''. 
********************************************************************************/


/************************* NewLpFIRfilter() *******************************/

FIRfilterState *NewLpFIRfilter( wc, upsample_factor, delay )
  double wc ;
  int    upsample_factor, *delay ;
{
  DeclareNew( FIRfilterState *, filter_state ) ;
  CoeffType *hn ;
  double    filterGain, hamming() ;
  int       n ;

 /***** generate and store FIR filter coefficients (linear phase, odd order, window desing technique) *****/
  filter_state->number_of_coeffs = ( NUMBER_OF_COEFFS + 1 ) / 2 ;  
  filter_state->coeffs = ( char * ) NewArray( CoeffType, filter_state->number_of_coeffs, "fir.c for coefficients\n" ) ;

  *delay = ( NUMBER_OF_COEFFS - 1 ) / 2 ;
  hn = ( CoeffType * ) filter_state->coeffs ;
  filterGain = ( double ) upsample_factor ;

  for( n = 0 ; n < filter_state->number_of_coeffs - 1 ; n++ ) 
      *hn++ = sin( wc * ( n - *delay ) ) / ( Pi * ( n - *delay ) ) * hamming( n, NUMBER_OF_COEFFS ) * filterGain ;
  *hn = wc / Pi * filterGain ;
    

 /***** initialise filter states *****/
  filter_state->number_of_states = NUMBER_OF_STATES ;
  filter_state->states = ( char * ) NewZeroedArray( StateType, NUMBER_OF_STATES, "fir.c for filter states\n" ) ;


 /***** return *****/   
  return( filter_state ) ;
}


/****************************** DoFIRfilter() *******************************/

void DoFIRfilter( filter_state, inoutput, points )
  FIRfilterState *filter_state ;
  DataType       *inoutput ;
  int            points ;
{
  register StateType  *st = ( StateType * ) filter_state->states ;
  register CoeffType  *cf = ( CoeffType * ) filter_state->coeffs ;
  register DataType   *inout_ptr = inoutput ;
  register double     acc ;
  register int        n, Ns = filter_state->number_of_states ;
  register int        Nc = filter_state->number_of_coeffs ;

 /***** for all points *****/
  for( ; points > 0 ; points-- ) {
      acc = 0. ;

     /*** shift the states ***/
      for( n = Ns - 1 ; n > 0 ; n-- ) 
          st[n] = st[n-1] ;
      st[0] = *inout_ptr ;
   
     /*** filter current point ***/
      for( n = 0  ; n < Nc - 1 ; n++ ) 
          acc += cf[n] * ( st[n] + st[Ns-1-n] ) ; 
      acc += cf[n] * st[n] ;

     /*** store output point ***/
      *inout_ptr++ = acc ;
  }  

 /***** return *****/
  return ;

}

/************************* CloseFIRfilter() *******************************/

void CloseFIRfilter( filter_state )
  FIRfilterState *filter_state ;
{
  Delete( filter_state->states ) ;
  Delete( filter_state->coeffs ) ;
  Delete( filter_state ) ;

  return ;

}


/*********************** low level functions ***********************/

double hamming( n, N )
  int n, N ;
{ 
  return ( 0.54 - 0.46 * cos( TwoPi * n / ( N - 1. ) ) ) ;
}