www.pudn.com > G711-729.rar > DE_ACELP.C

/* Version 3.3    Last modified: December 26, 1995 */ 
 
/*-----------------------------------------------------------* 
 *  Function  Decod_ACELP()                                  * 
 *  ~~~~~~~~~~~~~~~~~~~~~~~                                  * 
 *   Algebraic codebook decoder.                             * 
 *----------------------------------------------------------*/ 
 
#include "typedef.h" 
#include "basic_op.h" 
#include "ld8k.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