/*
 * Copyright 1992 by Jutta Degener and Carsten Bormann, Technische
 * Universitaet Berlin.  See the accompanying file "COPYRIGHT" for
 * details.  THERE IS ABSOLUTELY NO WARRANTY FOR THIS SOFTWARE.
 */

/* $Header: /home/kbs/jutta/src/gsm/gsm-1.0/src/RCS/preprocess.c,v 1.1 1992/10/28 00:15:50 jutta Exp $ */

#include	<stdio.h>
#include	<assert.h>

#include "private.h"

#include	"gsm.h"
#include 	"proto.h"

/*	4.2.0 .. 4.2.3	PREPROCESSING SECTION
 *  
 *  	After A-law to linear conversion (or directly from the
 *   	Ato D converter) the following scaling is assumed for
 * 	input to the RPE-LTP algorithm:
 *
 *      in:  0.1.....................12
 *	     S.v.v.v.v.v.v.v.v.v.v.v.v.*.*.*
 *
 *	Where S is the sign bit, v a valid bit, and * a "don't care" bit.
 * 	The original signal is called sop[..]
 *
 *      out:   0.1................... 12 
 *	     S.S.v.v.v.v.v.v.v.v.v.v.v.v.0.0
 */


void Gsm_Preprocess P3((S, s, so),
  struct gsm_state *S, word * s, word * so)
{                               /* [0..159]       IN/OUT  */

  word z1 = S->z1;
  longword L_z2 = S->L_z2;
  word mp = S->mp;

  word s1;
  longword L_s2;

  longword L_temp;

  word msp, lsp;
  word SO;

  longword ltmp;                /* for   ADD */
  ulongword utmp;               /* for L_ADD */

  register int k = 160;

  while (k--) {

    /*  4.2.1   Downscaling of the input signal
     */
    SO = SASR(*s, 3) << 2;
    s++;

    assert(SO >= -0x4000);      /* downscaled by     */
    assert(SO <= 0x3FFC);       /* previous routine. */


    /*  4.2.2   Offset compensation
     * 
     *  This part implements a high-pass filter and requires extended
     *  arithmetic precision for the recursive part of this filter.
     *  The input of this procedure is the array so[0...159] and the
     *  output the array sof[ 0...159 ].
     */
    /*   Compute the non-recursive part
     */

    s1 = SO - z1;               /* s1 = gsm_sub( *so, z1 ); */
    z1 = SO;

    assert(s1 != MIN_WORD);

    /*   Compute the recursive part
     */
    L_s2 = s1;
    L_s2 <<= 15;

    /*   Execution of a 31 bv 16 bits multiplication
     */

    msp = SASR(L_z2, 15);
    lsp = L_z2 - ((longword) msp << 15);        /* gsm_L_sub(L_z2,(msp<<15)); */

    L_s2 += GSM_MULT_R(lsp, 32735);
    L_temp = (longword) msp *32735;     /* GSM_L_MULT(msp,32735) >> 1; */
    L_z2 = GSM_L_ADD(L_temp, L_s2);

    /*    Compute sof[k] with rounding
     */
    L_temp = GSM_L_ADD(L_z2, 16384);

    /*   4.2.3  Preemphasis
     */

    msp = GSM_MULT_R(mp, -28180);
    mp = SASR(L_temp, 15);
    *so++ = GSM_ADD(mp, msp);
  }

  S->z1 = z1;
  S->L_z2 = L_z2;
  S->mp = mp;
}
