/*
   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
   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;
}