dec_lag3.c

g729a 语音编码,再linux c 环境下实现,有非常的好的移植性,通话质量好

/*
   ITU-T G.729 Annex C - Reference C code for floating point
                         implementation of G.729
                         Version 1.01 of 15.September.98
*/

/*
----------------------------------------------------------------------
                    COPYRIGHT NOTICE
----------------------------------------------------------------------
   ITU-T G.729 Annex C ANSI C source code
   Copyright (C) 1998, AT&T, France Telecom, NTT, University of
   Sherbrooke.  All rights reserved.

----------------------------------------------------------------------
*/

/*
 File : DEC_LAG3.C
 Used for the floating point version of both
 G.729 main body and G.729A
*/
#include "typedef.h"
#include "version.h"
#ifdef VER_G729A
 #include "ld8a.h"
#else
 #include "ld8k.h"
#endif

/*------------------------------------------------------------------------*
 *    Function dec_lag3                                                   *
 *             ~~~~~~~~                                                   *
 *   Decoding of fractional pitch lag with 1/3 resolution.                *
 * See "enc_lag3.c" for more details about the encoding procedure.        *
 *------------------------------------------------------------------------*/

void dec_lag3(     /* Decode the pitch lag                   */
  int index,       /* input : received pitch index           */
  int pit_min,     /* input : minimum pitch lag              */
  int pit_max,     /* input : maximum pitch lag              */
  int i_subfr,     /* input : subframe flag                  */
  int *T0,         /* output: integer part of pitch lag      */
  int *T0_frac     /* output: fractional part of pitch lag   */
)
{
  int i;
  int T0_min, T0_max;

  if (i_subfr == 0)                  /* if 1st subframe */
  {
    if (index < 197)
    {
       *T0 = (index+2)/3 + 19;
       *T0_frac = index - *T0*3 + 58;
    }
    else
    {
      *T0 = index - 112;
      *T0_frac = 0;
    }
  }

  else  /* second subframe */
  {
    /* find T0_min and T0_max for 2nd subframe */

    T0_min = *T0 - 5;
    if (T0_min < pit_min)
      T0_min = pit_min;

    T0_max = T0_min + 9;
    if(T0_max > pit_max)
    {
      T0_max = pit_max;
      T0_min = T0_max -9;
    }

    i = (index+2)/3 - 1;
    *T0 = i + T0_min;
    *T0_frac = index - 2 - i*3;
  }
  return;
}