/* * 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: /cvsroot/linphone/linphone/gsmlib/preprocess.c,v 1.1.1.1 2001/11/19 19:50:11 smorlat 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;}