src/GSM610/preprocess.c

/*
 * 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"

/*	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,
	int16_t		* s,
	int16_t		* so)		/* [0..159] 	IN/OUT	*/
{

	int16_t		z1 = S->z1 ;
	int32_t 	L_z2 = S->L_z2 ;
	int16_t		mp = S->mp ;

	int16_t		s1 ;
	int32_t	L_s2 ;

	int32_t	L_temp ;

	int16_t		msp, lsp ;
	int16_t		SO ;

	register int		k = 160 ;

	while (k--)
	{

		/*  4.2.1   Downscaling of the input signal */
		SO = arith_shift_left (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 = arith_shift_left (L_s2, 15) ;

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

		msp = SASR_L (L_z2, 15) ;
		lsp = L_z2 - arith_shift_left ((int32_t) msp, 15) ; /* gsm_L_sub (L_z2,(msp<<15)) ; */

		L_s2 += GSM_MULT_R (lsp, 32735) ;
		L_temp = (int32_t) 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 ;
}