/*

 * 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: /tmp_amd/presto/export/kbs/jutta/src/gsm/RCS/preprocess.c,v 1.2 1994/05/10 20:18:45 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;

}