www.pudn.com > g729_audio_encode.rar > dec_lag3.c

/* 
   ITU-T G.729 Speech Coder ANSI-C Source Code 
   Version 3.3    Last modified: December 26, 1995 
 
   Copyright (c) 1996, 
   AT&T, France Telecom, NTT, Universite de Sherbrooke, Lucent Technologies 
   All rights reserved. 
*/ 
 
/*------------------------------------------------------------------------* 
 *    Function Dec_lag3                                                   * 
 *             ~~~~~~~~                                                   * 
 *   Decoding of fractional pitch lag with 1/3 resolution.                * 
 * See "Enc_lag3.c" for more details about the encoding procedure.        * 
 *------------------------------------------------------------------------*/ 
 
#include "typedef.h" 
#include "basic_op.h" 
#include "ld8k.h" 
 
void Dec_lag3( 
  Word16 index,       /* input : received pitch index           */ 
  Word16 pit_min,     /* input : minimum pitch lag              */ 
  Word16 pit_max,     /* input : maximum pitch lag              */ 
  Word16 i_subfr,     /* input : subframe flag                  */ 
  Word16 *T0,         /* output: integer part of pitch lag      */ 
  Word16 *T0_frac     /* output: fractional part of pitch lag   */ 
) 
{ 
  Word16 i; 
  Word16 T0_min, T0_max; 
 
  if (i_subfr == 0)                  /* if 1st subframe */ 
  { 
    if (sub(index, 197) < 0) 
    { 
      /* *T0 = (index+2)/3 + 19 */ 
 
      *T0 = add(mult(add(index, 2), 10923), 19); 
 
      /* *T0_frac = index - *T0*3 + 58 */ 
 
      i = add(add(*T0, *T0), *T0); 
      *T0_frac = add(sub(index, i), 58); 
    } 
    else 
    { 
      *T0 = sub(index, 112); 
      *T0_frac = 0; 
    } 
 
  } 
 
  else  /* second subframe */ 
  { 
    /* find T0_min and T0_max for 2nd subframe */ 
 
    T0_min = sub(*T0, 5); 
    if (sub(T0_min, pit_min) < 0) 
    { 
      T0_min = pit_min; 
    } 
 
    T0_max = add(T0_min, 9); 
    if (sub(T0_max, pit_max) > 0) 
    { 
      T0_max = pit_max; 
      T0_min = sub(T0_max, 9); 
    } 
 
    /* i = (index+2)/3 - 1 */ 
    /* *T0 = i + t0_min;    */ 
 
    i = sub(mult(add(index, 2), 10923), 1); 
    *T0 = add(i, T0_min); 
 
    /* t0_frac = index - 2 - i*3; */ 
 
    i = add(add(i, i), i); 
    *T0_frac = sub(sub(index, 2), i); 
  } 
 
  return; 
}