/*
 * Copyright: (C) 2000 Julius O. Smith
 *
 *   This library is free software; you can redistribute it and/or
 *   modify it under the terms of the GNU Lesser General Public
 *   License as published by the Free Software Foundation; either
 *   version 2.1 of the License, or any later version.
 *
 *   This library is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *   Lesser General Public License for more details.
 *
 *   You should have received a copy of the GNU Lesser General Public
 *   License along with this library; if not, write to the Free Software
 *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
 *
 *   Julius O. Smith  jos@ccrma.stanford.edu
 *
 */
/* This code was modified by Bruce Forsberg (forsberg@tns.net) to make it
   into a C++ class
*/

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>

#include "aflibConverter.h"
#include "aflibConverterLargeFilter.h"
#include "aflibConverterSmallFilter.h"

#include "aflibDebug.h"

#if (!defined(TRUE) || !defined(FALSE))
# define TRUE 1
# define FALSE 0
#endif                                                                                   


/*
 * The configuration constants below govern
 * the number of bits in the input sample and filter coefficients, the
 * number of bits to the right of the binary-point for fixed-point math, etc.
 */

/* Conversion constants */
#define Nhc       8
#define Na        7
#define Np       (Nhc+Na)
#define Npc      (1<<Nhc)
#define Amask    ((1<<Na)-1)
#define Pmask    ((1<<Np)-1)
#define Nh       16
#define Nb       16
#define Nhxn     14
#define Nhg      (Nh-Nhxn)
#define NLpScl   13
/* Description of constants:
 *
 * Npc - is the number of look-up values available for the lowpass filter
 *    between the beginning of its impulse response and the "cutoff time"
 *    of the filter.  The cutoff time is defined as the reciprocal of the
 *    lowpass-filter cut off frequence in Hz.  For example, if the
 *    lowpass filter were a sinc function, Npc would be the index of the
 *    impulse-response lookup-table corresponding to the first zero-
 *    crossing of the sinc function.  (The inverse first zero-crossing
 *    time of a sinc function equals its nominal cutoff frequency in Hz.)
 *    Npc must be a power of 2 due to the details of the current
 *    implementation. The default value of 512 is sufficiently high that
 *    using linear interpolation to fill in between the table entries
 *    gives approximately 16-bit accuracy in filter coefficients.
 *
 * Nhc - is log base 2 of Npc.
 *
 * Na - is the number of bits devoted to linear interpolation of the
 *    filter coefficients.
 *
 * Np - is Na + Nhc, the number of bits to the right of the binary point
 *    in the integer "time" variable. To the left of the point, it indexes
 *    the input array (X), and to the right, it is interpreted as a number
 *    between 0 and 1 sample of the input X.  Np must be less than 16 in
 *    this implementation.
 *
 * Nh - is the number of bits in the filter coefficients. The sum of Nh and
 *    the number of bits in the input data (typically 16) cannot exceed 32.
 *    Thus Nh should be 16.  The largest filter coefficient should nearly
 *    fill 16 bits (32767).
 *
 * Nb - is the number of bits in the input data. The sum of Nb and Nh cannot
 *    exceed 32.
 *
 * Nhxn - is the number of bits to right shift after multiplying each input
 *    sample times a filter coefficient. It can be as great as Nh and as
 *    small as 0. Nhxn = Nh-2 gives 2 guard bits in the multiply-add
 *    accumulation.  If Nhxn=0, the accumulation will soon overflow 32 bits.
 *
 * Nhg - is the number of guard bits in mpy-add accumulation (equal to Nh-Nhxn)
 *
 * NLpScl - is the number of bits allocated to the unity-gain normalization
 *    factor.  The output of the lowpass filter is multiplied by LpScl and
 *    then right-shifted NLpScl bits. To avoid overflow, we must have
 *    Nb+Nhg+NLpScl < 32.
 */




aflibConverter::aflibConverter(
   bool  high_quality,
   bool  linear_interpolation,
   bool  filter_interpolation)
{
	/* TODO put all these into an enum as it only makes sense to have 
	 * one true at a time. - DAS
	 */
   interpFilt = filter_interpolation;
   largeFilter = high_quality;
   linearInterp = linear_interpolation;

   _I = NULL;
   _J = NULL;
   _vol = 1.0;
}

aflibConverter::~aflibConverter()
{
   deleteMemory();
}


void
aflibConverter::deleteMemory()
{
   int i;

   // Delete memory for the input and output arrays
   if (_I != NULL)
   {
      for (i = 0; i < _nChans; i++)
      {
         delete [] _I[i];
         _I[i] = NULL;
         delete [] _J[i];
         _J[i] = NULL;
      }
      delete [] _I;
      _I = NULL;
      delete [] _J;
      _J = NULL;
   }
}

void
aflibConverter::initialize(
   double fac,
   int    channels,
   double volume)
{
// This function will allow one to stream data. When a new data stream is to
// be input then this function should be called. Even if the factor and number
// of channels don't change. Otherwise each new data block sent to resample
// will be considered part of the previous data block. This function also allows
// one to specified a multiplication factor to adjust the final output. This
// applies to the small and large filter.

   int i;

   // Delete all previous allocated input and output buffer memory
   deleteMemory();

   _factor = fac;
   _nChans = channels;
   _initial = TRUE;
   _vol = volume;

   // Allocate all new memory
   _I = new short * [_nChans];
   _J = new short * [_nChans];

   for (i = 0; i < _nChans; i++)
   {
      // Add extra to allow of offset of input data (Xoff in main routine)
      _I[i] = new short[IBUFFSIZE + 256];
      _J[i] = new short[(int)(((double)IBUFFSIZE)*_factor)];
      memset(_I[i], 0, sizeof(short) * (IBUFFSIZE + 256));    
   }
}

int
aflibConverter::resample(       /* number of output samples returned */
    int& inCount,               /* number of input samples to convert */
    int outCount,               /* number of output samples to compute */
    short inArray[],            /* input data */
    short outArray[])           /* output data */
{
   int Ycount;


   // Use fast method with no filtering. Poor quality
   if (linearInterp == TRUE)
      Ycount = resampleFast(inCount,outCount,inArray,outArray);
   // Use small filtering. Good qulaity
   else if (largeFilter == FALSE)
      Ycount = resampleWithFilter(inCount,outCount,inArray,outArray,
         SMALL_FILTER_IMP, SMALL_FILTER_IMPD, 
	(unsigned short)(SMALL_FILTER_SCALE * _vol),
         SMALL_FILTER_NMULT, SMALL_FILTER_NWING);
   // Use large filtering Great quality
   else
      Ycount = resampleWithFilter(inCount,outCount,inArray,outArray,
         LARGE_FILTER_IMP, LARGE_FILTER_IMPD, 
	(unsigned short)(LARGE_FILTER_SCALE * _vol),
         LARGE_FILTER_NMULT, LARGE_FILTER_NWING);                               

   _initial = FALSE;

   return (Ycount);
}



int
aflibConverter::err_ret(char *s)
{
    aflib_debug("resample: %s \n\n",s); /* Display error message  */
    return -1;
}

int
aflibConverter::readData(
         int   inCount,       /* _total_ number of frames in input file */
         short inArray[],     /* input data */
         short *outPtr[],     /* array receiving chan samps */
         int   dataArraySize, /* size of these arrays */
         int   Xoff,          /* read into input array starting at this index */
         bool  init_count) 
{
   int    i, Nsamps, c;
   static unsigned int framecount;  /* frames previously read */
   short *ptr;

   if (init_count == TRUE)
      framecount = 0;       /* init this too */

   Nsamps = dataArraySize - Xoff;   /* Calculate number of samples to get */

   // Don't overrun input buffers
   if (Nsamps > (inCount - (int)framecount))
   {
      Nsamps = inCount - framecount;
   }

   for (c = 0; c < _nChans; c++)
   {
      ptr = outPtr[c];
      ptr += Xoff;        /* Start at designated sample number */

      for (i = 0; i < Nsamps; i++)
         *ptr++ = (short) inArray[c * inCount + i + framecount];
   }

   framecount += Nsamps;

   if ((int)framecount >= inCount)            /* return index of last samp */
      return (((Nsamps - (framecount - inCount)) - 1) + Xoff);
   else
      return 0;
}

int
aflibConverter::SrcLinear(
   short X[],
   short Y[],
   double factor,
   unsigned int *Time,
   unsigned short& Nx,
   unsigned short Nout)
{
	short iconst;
	short *Xp, *Ystart;
	int v,x1,x2;

	double dt;                  /* Step through input signal */ 
	unsigned int dtb;           /* Fixed-point version of Dt */
//	unsigned int endTime;       /* When Time reaches EndTime, return to user */
	unsigned int start_sample, end_sample;

	dt = 1.0/factor;            /* Output sampling period */
	dtb = (unsigned int)(dt*(1<<Np) + 0.5); /* Fixed-point representation */

	start_sample = (*Time)>>Np;
	Ystart = Y;
//	endTime = *Time + (1<<Np)*(int)Nx;
	/* 
	* TODO
	* DAS: not sure why this was changed from *Time < endTime
	* update: *Time < endTime causes seg fault.  Also adds a clicking sound.
	*/
	while (Y - Ystart != Nout)
//	while (*Time < endTime)
	{
		iconst = (*Time) & Pmask;
		Xp = &X[(*Time)>>Np];      /* Ptr to current input sample */
		x1 = *Xp++;
		x2 = *Xp;
		x1 *= ((1<<Np)-iconst);
		x2 *= iconst;
		v = x1 + x2;
		*Y++ = WordToHword(v,Np);   /* Deposit output */
		*Time += dtb;		    /* Move to next sample by time increment */
	}
	end_sample = (*Time)>>Np;
	Nx = end_sample - start_sample;
	return (Y - Ystart);            /* Return number of output samples */
}


int
aflibConverter::SrcUp(
   short X[],
   short Y[],
   double factor,
   unsigned int *Time,
   unsigned short& Nx,
   unsigned short Nout,
   unsigned short Nwing,
   unsigned short LpScl,
   short Imp[],
   short ImpD[],
   bool Interp)
{
	short *Xp, *Ystart;
	int v;

	double dt;                  /* Step through input signal */ 
	unsigned int dtb;           /* Fixed-point version of Dt */
//	unsigned int endTime;       /* When Time reaches EndTime, return to user */
	unsigned int start_sample, end_sample;

	dt = 1.0/factor;            /* Output sampling period */
	dtb = (unsigned int)(dt*(1<<Np) + 0.5); /* Fixed-point representation */

	start_sample = (*Time)>>Np;
	Ystart = Y;
//	endTime = *Time + (1<<Np)*(int)Nx;
	/* 
	* TODO
	* DAS: not sure why this was changed from *Time < endTime
	* update: *Time < endTime causes seg fault.  Also adds a clicking sound.
	*/
	while (Y - Ystart != Nout)
//	while (*Time < endTime)
	{
		Xp = &X[*Time>>Np];      /* Ptr to current input sample */
		/* Perform left-wing inner product */
		v = FilterUp(Imp, ImpD, Nwing, Interp, Xp, (short)(*Time&Pmask),-1);
		/* Perform right-wing inner product */
		v += FilterUp(Imp, ImpD, Nwing, Interp, Xp+1, 
                       (short)((((*Time)^Pmask)+1)&Pmask), 1);
		v >>= Nhg;		/* Make guard bits */
		v *= LpScl;		/* Normalize for unity filter gain */
		*Y++ = WordToHword(v,NLpScl);   /* strip guard bits, deposit output */
		*Time += dtb;		/* Move to next sample by time increment */
	}
	end_sample = (*Time)>>Np;
	Nx = end_sample - start_sample;
	return (Y - Ystart);        /* Return the number of output samples */
}



int
aflibConverter::SrcUD(
   short X[],
   short Y[],
   double factor,
   unsigned int *Time,
   unsigned short& Nx,
   unsigned short Nout,
   unsigned short Nwing,
   unsigned short LpScl,
   short Imp[],
   short ImpD[],
   bool Interp)
{
	short *Xp, *Ystart;
	int v;

	double dh;                  /* Step through filter impulse response */
	double dt;                  /* Step through input signal */
//	unsigned int endTime;       /* When Time reaches EndTime, return to user */
	unsigned int dhb, dtb;      /* Fixed-point versions of Dh,Dt */
	unsigned int start_sample, end_sample;

	dt = 1.0/factor;            /* Output sampling period */
	dtb = (unsigned int)(dt*(1<<Np) + 0.5); /* Fixed-point representation */

	dh = MIN(Npc, factor*Npc);  /* Filter sampling period */
	dhb = (unsigned int)(dh*(1<<Na) + 0.5); /* Fixed-point representation */

	start_sample = (*Time)>>Np;
	Ystart = Y;
//	endTime = *Time + (1<<Np)*(int)Nx;
	/* 
	* TODO
	* DAS: not sure why this was changed from *Time < endTime
	* update: *Time < endTime causes seg fault.  Also adds a clicking sound.
	*/
	while (Y - Ystart != Nout)
//	while (*Time < endTime)
	{
		Xp = &X[*Time>>Np];	/* Ptr to current input sample */
		v = FilterUD(Imp, ImpD, Nwing, Interp, Xp, (short)(*Time&Pmask),
				  -1, dhb);	/* Perform left-wing inner product */
		v += FilterUD(Imp, ImpD, Nwing, Interp, Xp+1, 
                       (short)((((*Time)^Pmask)+1)&Pmask), 1, dhb);	/* Perform right-wing inner product */
		v >>= Nhg;		/* Make guard bits */
		v *= LpScl;		/* Normalize for unity filter gain */
		*Y++ = WordToHword(v,NLpScl);   /* strip guard bits, deposit output */
		*Time += dtb;		/* Move to next sample by time increment */
	}
	
	end_sample = (*Time)>>Np;
	Nx = end_sample - start_sample;
	return (Y - Ystart);        /* Return the number of output samples */
}


int
aflibConverter::resampleFast(  /* number of output samples returned */
    int& inCount,		/* number of input samples to convert */
    int outCount,		/* number of output samples to compute */
    short inArray[],            /* input data */
    short outArray[])           /* output data */
{
    unsigned int Time2;		/* Current time/pos in input sample */
#if 0
    unsigned short Ncreep;
#endif
    unsigned short Xp, Xoff, Xread;
    int OBUFFSIZE = (int)(((double)IBUFFSIZE)*_factor);
    unsigned short Nout = 0, Nx, orig_Nx;
    unsigned short maxOutput;
    int total_inCount = 0;
    int c, i, Ycount, last;
    bool first_pass = TRUE;


    Xoff = 10;

    Nx = IBUFFSIZE - 2*Xoff;     /* # of samples to process each iteration */
    last = 0;			/* Have not read last input sample yet */
    Ycount = 0;			/* Current sample and length of output file */

    Xp = Xoff;			/* Current "now"-sample pointer for input */
    Xread = Xoff;		/* Position in input array to read into */

    if (_initial == TRUE)
       _Time = (Xoff<<Np);	/* Current-time pointer for converter */

    do {
		if (!last)		/* If haven't read last sample yet */
		{
	   	 last = readData(inCount, inArray, _I, 
					 IBUFFSIZE, (int)Xread,first_pass);
          first_pass = FALSE;
	    	 if (last && (last-Xoff<Nx)) { /* If last sample has been read... */
				Nx = last-Xoff;	/* ...calc last sample affected by filter */
			 	if (Nx <= 0)
		  			break;
	    	 }
		}

      if ((outCount-Ycount) > (OBUFFSIZE - (2*Xoff*_factor)) )
      	maxOutput = OBUFFSIZE - (unsigned short)(2*Xoff*_factor);
      else
      	maxOutput = outCount-Ycount;

      for (c = 0; c < _nChans; c++)
      {
			orig_Nx = Nx;
	   	Time2 = _Time;
	   /* Resample stuff in input buffer */
	   	Nout=SrcLinear(_I[c],_J[c],_factor,&Time2,orig_Nx,maxOutput);
      }
		Nx = orig_Nx;
      _Time = Time2;

		_Time -= (Nx<<Np);	/* Move converter Nx samples back in time */
		Xp += Nx;		/* Advance by number of samples processed */
#if 0
	Ncreep = (Time>>Np) - Xoff; /* Calc time accumulation in Time */
	if (Ncreep) {
	    Time -= (Ncreep<<Np);    /* Remove time accumulation */
	    Xp += Ncreep;            /* and add it to read pointer */
	}
#endif
      for (c = 0; c < _nChans; c++)
      {
	   	for (i=0; i<IBUFFSIZE-Xp+Xoff; i++) { /* Copy part of input signal */
	       	_I[c][i] = _I[c][i+Xp-Xoff]; /* that must be re-used */
	   	}
      }
		if (last) {		/* If near end of sample... */
	    	last -= Xp;		/* ...keep track were it ends */
	    	if (!last)		/* Lengthen input by 1 sample if... */
	      	last++;		/* ...needed to keep flag TRUE */
		}
		Xread = IBUFFSIZE - Nx;	/* Pos in input buff to read new data into */
		Xp = Xoff;
	
		Ycount += Nout;
		if (Ycount>outCount) {
	    	Nout -= (Ycount-outCount);
	    	Ycount = outCount;
		}

		if (Nout > OBUFFSIZE) /* Check to see if output buff overflowed */
	 		return err_ret("Output array overflow");

      for (c = 0; c < _nChans; c++)
	   	for (i = 0; i < Nout; i++)
            outArray[c * outCount + i + Ycount - Nout] = _J[c][i];

      total_inCount += Nx;

    } while (Ycount < outCount); /* Continue until done */

    inCount = total_inCount;

    return(Ycount);		/* Return # of samples in output file */
}


int
aflibConverter::resampleWithFilter(  /* number of output samples returned */
    int& inCount,		/* number of input samples to convert */
    int outCount,		/* number of output samples to compute */
    short inArray[],            /* input data */
    short outArray[],           /* output data */
    short Imp[], short ImpD[],
    unsigned short LpScl, unsigned short Nmult, unsigned short Nwing)
{
    unsigned int Time2;		/* Current time/pos in input sample */
#if 0
    unsigned short Ncreep;
#endif
    unsigned short Xp, Xoff, Xread;
    int OBUFFSIZE = (int)(((double)IBUFFSIZE)*_factor);
    unsigned short Nout = 0, Nx, orig_Nx;
    unsigned short maxOutput;
    int total_inCount = 0;
    int c, i, Ycount, last;
    bool first_pass = TRUE;


    /* Account for increased filter gain when using factors less than 1 */
    if (_factor < 1)
      LpScl = (unsigned short)(LpScl*_factor + 0.5);

    /* Calc reach of LP filter wing & give some creeping room */
    Xoff = (unsigned short)(((Nmult+1)/2.0) * MAX(1.0,1.0/_factor) + 10);

    if (IBUFFSIZE < 2*Xoff)      /* Check input buffer size */
      return err_ret("IBUFFSIZE (or factor) is too small");

    Nx = IBUFFSIZE - 2*Xoff;     /* # of samples to process each iteration */
    
    last = 0;			/* Have not read last input sample yet */
    Ycount = 0;			/* Current sample and length of output file */
    Xp = Xoff;			/* Current "now"-sample pointer for input */
    Xread = Xoff;		/* Position in input array to read into */

    if (_initial == TRUE)
       _Time = (Xoff<<Np);	/* Current-time pointer for converter */
    
    do {
		if (!last)		/* If haven't read last sample yet */
		{
	    	last = readData(inCount, inArray, _I, 
					IBUFFSIZE, (int)Xread,first_pass);
         first_pass = FALSE;
	    	if (last && (last-Xoff<Nx)) { /* If last sample has been read... */
				Nx = last-Xoff;	/* ...calc last sample affected by filter */
				if (Nx <= 0)
		  			break;
	    	}
		}

      if ( (outCount-Ycount) > (OBUFFSIZE - (2*Xoff*_factor)) )
      	maxOutput = OBUFFSIZE  - (unsigned short)(2*Xoff*_factor);
      else
      	maxOutput = outCount-Ycount;

      for (c = 0; c < _nChans; c++)
      {
			orig_Nx = Nx;
	   	Time2 = _Time;
           /* Resample stuff in input buffer */
	   	if (_factor >= 1) {	/* SrcUp() is faster if we can use it */
	       	Nout=SrcUp(_I[c],_J[c],_factor,
						&Time2,Nx,maxOutput,Nwing,LpScl,Imp,ImpD,interpFilt);
	   	}
	   	else {
	       	Nout=SrcUD(_I[c],_J[c],_factor,
						&Time2,Nx,maxOutput,Nwing,LpScl,Imp,ImpD,interpFilt);
	   	}
      }
      _Time = Time2;

		_Time -= (Nx<<Np);	/* Move converter Nx samples back in time */
		Xp += Nx;		/* Advance by number of samples processed */
#if 0
	Ncreep = (Time>>Np) - Xoff; /* Calc time accumulation in Time */
	if (Ncreep) {
	    Time -= (Ncreep<<Np);    /* Remove time accumulation */
	    Xp += Ncreep;            /* and add it to read pointer */
	}
#endif
		if (last) {		/* If near end of sample... */
			 last -= Xp;		/* ...keep track were it ends */
			 if (!last)		/* Lengthen input by 1 sample if... */
				last++;		/* ...needed to keep flag TRUE */
		}
		
		Ycount += Nout;
		if (Ycount > outCount) {
			 Nout -= (Ycount - outCount);
			 Ycount = outCount;
		}

		if (Nout > OBUFFSIZE) /* Check to see if output buff overflowed */
		  return err_ret("Output array overflow");
		
	   for (c = 0; c < _nChans; c++)
		{
			for (i = 0; i < Nout; i++)
			{
				outArray[c * outCount + i + Ycount - Nout] = _J[c][i];
			}
		}

		int act_incount = (int)Nx;

		for (c = 0; c < _nChans; c++)
		{
			for (i=0; i<IBUFFSIZE-act_incount+Xoff; i++) { /* Copy part of input signal */
				 _I[c][i] = _I[c][i+act_incount]; /* that must be re-used */
			}
		}
		Xread = IBUFFSIZE - Nx; /* Pos in input buff to read new data into */
		Xp = Xoff;

		total_inCount += Nx;

    } while (Ycount < outCount); /* Continue until done */

    inCount = total_inCount;

    return(Ycount);		/* Return # of samples in output file */
}

int
aflibConverter::FilterUp(
	short Imp[], 
	short ImpD[], 
	unsigned short Nwing, 
	bool Interp,
	short *Xp, 
	short Ph, 
	short Inc)
{
	short *Hp, *Hdp = NULL, *End;
	short a = 0;
	int v, t;

	v=0;
	Hp = &Imp[Ph>>Na];
	End = &Imp[Nwing];
	
	if (Interp) 
	{
		Hdp = &ImpD[Ph>>Na];
		a = Ph & Amask;
	}
	
	if (Inc == 1)		/* If doing right wing...              */
	{				/* ...drop extra coeff, so when Ph is  */
		End--;			/*    0.5, we don't do too many mult's */
		if (Ph == 0)		/* If the phase is zero...           */
		{			/* ...then we've already skipped the */
			 Hp += Npc;		/*    first sample, so we must also  */
			 Hdp += Npc;		/*    skip ahead in Imp[] and ImpD[] */
		}
	}
	
	if (Interp)
	{
		while (Hp < End) 
		{
			t = *Hp;		/* Get filter coeff */
			t += (((int)*Hdp)*a)>>Na; /* t is now interp'd filter coeff */
			Hdp += Npc;		/* Filter coeff differences step */
			t *= *Xp;		/* Mult coeff by input sample */
			if (t & (1<<(Nhxn-1)))  /* Round, if needed */
				t += (1<<(Nhxn-1));
			t >>= Nhxn;		/* Leave some guard bits, but come back some */
			v += t;			/* The filter output */
			Hp += Npc;		/* Filter coeff step */
			Xp += Inc;		/* Input signal step. NO CHECK ON BOUNDS */
		}
	}	
	else 
	{
		while (Hp < End) 
		{
			t = *Hp;		/* Get filter coeff */
			t *= *Xp;		/* Mult coeff by input sample */
			if (t & (1<<(Nhxn-1)))  /* Round, if needed */
				t += (1<<(Nhxn-1));
			t >>= Nhxn;		/* Leave some guard bits, but come back some */
			v += t;			/* The filter output */
			Hp += Npc;		/* Filter coeff step */
			Xp += Inc;		/* Input signal step. NO CHECK ON BOUNDS */
		}
	}
	return(v);
}


int
aflibConverter::FilterUD( 
	short Imp[], 
	short ImpD[],
	unsigned short Nwing, 
	bool Interp,
	short *Xp, 
	short Ph, 
	short Inc, 
	unsigned short dhb)
{
	short a;
	short *Hp, *Hdp, *End;
	int v, t;
	unsigned int Ho;

	v=0;
	Ho = (Ph*(unsigned int)dhb)>>Np;
	End = &Imp[Nwing];
	if (Inc == 1)		/* If doing right wing...              */
	{				/* ...drop extra coeff, so when Ph is  */
		End--;			/*    0.5, we don't do too many mult's */
		if (Ph == 0)		/* If the phase is zero...           */
			Ho += dhb;		/* ...then we've already skipped the */
	}				/*    first sample, so we must also  */
			/*    skip ahead in Imp[] and ImpD[] */
	
	if (Interp)
	{
		while ((Hp = &Imp[Ho>>Na]) < End) 
		{
			t = *Hp;		/* Get IR sample */
			Hdp = &ImpD[Ho>>Na];  /* get interp (lower Na) bits from diff table*/
			a = Ho & Amask;	/* a is logically between 0 and 1 */
			t += (((int)*Hdp)*a)>>Na; /* t is now interp'd filter coeff */
			t *= *Xp;		/* Mult coeff by input sample */
			if (t & 1<<(Nhxn-1))	/* Round, if needed */
				t += 1<<(Nhxn-1);
			t >>= Nhxn;		/* Leave some guard bits, but come back some */
			v += t;			/* The filter output */
			Ho += dhb;		/* IR step */
			Xp += Inc;		/* Input signal step. NO CHECK ON BOUNDS */
		}
	}
	else 
	{
		while ((Hp = &Imp[Ho>>Na]) < End) 
		{
			t = *Hp;		/* Get IR sample */
			t *= *Xp;		/* Mult coeff by input sample */
			if (t & 1<<(Nhxn-1))	/* Round, if needed */
				t += 1<<(Nhxn-1);
			t >>= Nhxn;		/* Leave some guard bits, but come back some */
			v += t;			/* The filter output */
			Ho += dhb;		/* IR step */
			Xp += Inc;		/* Input signal step. NO CHECK ON BOUNDS */
		}
	}
	return(v);
}

