de_acelp.c

/* ITU-T G.729 Software Package Release 2 (November 2006) */
/*
 ITU-T G.729A Speech Coder    ANSI-C Source Code
 Version 1.1    Last modified: September 1996

 Copyright (c) 1996,
 AT&T, France Telecom, NTT, Universite de Sherbrooke, Lucent Technologies
 All rights reserved.
 */

/*-----------------------------------------------------------*
 *  Function  Decod_ACELP()                                  *
 *  ~~~~~~~~~~~~~~~~~~~~~~~                                  *
 *   Algebraic codebook decoder.                             *
 *----------------------------------------------------------*/

#include "typedef.h"
#include "basic_op.h"
#include "ld8a.h"

void Decod_ACELP(Word16 sign, /* (i)     : signs of 4 pulses.                       */
Word16 index, /* (i)     : Positions of the 4 pulses.               */
Word16 cod[] /* (o) Q13 : algebraic (fixed) codebook excitation    */
) {
	Word16 i, j;
	Word16 pos[4];

	/* Decode the positions */

	i = index & (Word16) 7;
	pos[0] = add(i, shl(i, 2)); /* pos0 =i*5 */

	index = shr(index, 3);
	i = index & (Word16) 7;
	i = add(i, shl(i, 2)); /* pos1 =i*5+1 */
	pos[1] = add(i, 1);

	index = shr(index, 3);
	i = index & (Word16) 7;
	i = add(i, shl(i, 2)); /* pos2 =i*5+1 */
	pos[2] = add(i, 2);

	index = shr(index, 3);
	j = index & (Word16) 1;
	index = shr(index, 1);
	i = index & (Word16) 7;
	i = add(i, shl(i, 2)); /* pos3 =i*5+3+j */
	i = add(i, 3);
	pos[3] = add(i, j);

	/* decode the signs  and build the codeword */

	for (i = 0; i < L_SUBFR; i++) {
		cod[i] = 0;
	}

	for (j = 0; j < 4; j++) {

		i = sign & (Word16) 1;
		sign = shr(sign, 1);

		if (i != 0) {
			cod[pos[j]] = 8191; /* Q13 +1.0 */
		} else {
			cod[pos[j]] = -8192; /* Q13 -1.0 */
		}
	}

	return;
}