text: /*
   * 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.
   */
  
  #include	<stdio.h>
  #include	<assert.h>
  
  #include "gsm610_priv.h"
  
  #include	"gsm.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 (
  	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;
  
  	register int		k = 160;
  
  	while (k--) {
  
  	/*  4.2.1   Downscaling of the input signal
  	 */
  		SO = SASR_W( *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( 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( L_temp, 15 );
  		*so++ = GSM_ADD( mp, msp );
  	}
  
  	S->z1   = z1;
  	S->L_z2 = L_z2;
  	S->mp   = mp;
  }
  /*
  ** Do not edit or modify anything in this comment block.
  ** The arch-tag line is a file identity tag for the GNU Arch 
  ** revision control system.
  **
  ** arch-tag: b760b0d9-3a05-4da3-9dc9-441ffb905d87
  */
  
  