dspfunc.c

C源程序---G.729a语音代码G.729a语音代码

/*
   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.
*/

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

#include "ld8a.h"
#include "tab_ld8a.h"

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : Pow2()                                                  |
 |                                                                           |
 |     L_x = pow(2.0, exponent.fraction)                                     |
 |---------------------------------------------------------------------------|
 |  Algorithm:                                                               |
 |                                                                           |
 |   The function Pow2(L_x) is approximated by a table and linear            |
 |   interpolation.                                                          |
 |                                                                           |
 |   1- i = bit10-b15 of fraction,   0 <= i <= 31                            |
 |   2- a = bit0-b9   of fraction                                            |
 |   3- L_x = tabpow[i]<<16 - (tabpow[i] - tabpow[i+1]) * a * 2                 |
 |   4- L_x = L_x >> (30-exponent)     (with rounding)                       |
 |___________________________________________________________________________|
*/


Word32 Pow2(        /* (o) Q0  : result       (range: 0<=val<=0x7fffffff) */
  Word16 exponent,  /* (i) Q0  : Integer part.      (range: 0<=val<=30)   */
  Word16 fraction   /* (i) Q15 : Fractional part.   (range: 0.0<=val<1.0) */
)
{
  Word16 exp, i, a, tmp;
  Word32 L_x;

  L_x = L_mult(fraction, 32);           /* L_x = fraction<<6           */
  i   = extract_h(L_x);                 /* Extract b10-b15 of fraction */
  L_x = L_shr(L_x, 1);
  a   = extract_l(L_x);                 /* Extract b0-b9   of fraction */
  a   = a & (Word16)0x7fff;

  L_x = L_deposit_h(tabpow[i]);         /* tabpow[i] << 16        */
  tmp = sub(tabpow[i], tabpow[i+1]);    /* tabpow[i] - tabpow[i+1] */
  L_x = L_msu(L_x, tmp, a);             /* L_x -= tmp*a*2        */

  exp = sub(30, exponent);
  L_x = L_shr_r(L_x, exp);

  return(L_x);
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : Log2()                                                  |
 |                                                                           |
 |       Compute log2(L_x).                                                  |
 |       L_x is positive.                                                    |
 |                                                                           |
 |       if L_x is negative or zero, result is 0.                            |
 |---------------------------------------------------------------------------|
 |  Algorithm:                                                               |
 |                                                                           |
 |   The function Log2(L_x) is approximated by a table and linear            |
 |   interpolation.                                                          |
 |                                                                           |
 |   1- Normalization of L_x.                                                |
 |   2- exponent = 30-exponent                                               |
 |   3- i = bit25-b31 of L_x,    32 <= i <= 63  ->because of normalization.  |
 |   4- a = bit10-b24                                                        |
 |   5- i -=32                                                               |
 |   6- fraction = tablog[i]<<16 - (tablog[i] - tablog[i+1]) * a * 2            |
 |___________________________________________________________________________|
*/

void Log2(
  Word32 L_x,       /* (i) Q0 : input value                                 */
  Word16 *exponent, /* (o) Q0 : Integer part of Log2.   (range: 0<=val<=30) */
  Word16 *fraction  /* (o) Q15: Fractional  part of Log2. (range: 0<=val<1) */
)
{
  Word16 exp, i, a, tmp;
  Word32 L_y;

  if( L_x <= (Word32)0 )
  {
    *exponent = 0;
    *fraction = 0;
    return;
  }

  exp = norm_l(L_x);
  L_x = L_shl(L_x, exp );               /* L_x is normalized */

  *exponent = sub(30, exp);

  L_x = L_shr(L_x, 9);
  i   = extract_h(L_x);                 /* Extract b25-b31 */
  L_x = L_shr(L_x, 1);
  a   = extract_l(L_x);                 /* Extract b10-b24 of fraction */
  a   = a & (Word16)0x7fff;

  i   = sub(i, 32);

  L_y = L_deposit_h(tablog[i]);         /* tablog[i] << 16        */
  tmp = sub(tablog[i], tablog[i+1]);    /* tablog[i] - tablog[i+1] */
  L_y = L_msu(L_y, tmp, a);             /* L_y -= tmp*a*2        */

  *fraction = extract_h( L_y);

  return;
}

/*___________________________________________________________________________
 |                                                                           |
 |   Function Name : Inv_sqrt                                                |
 |                                                                           |
 |       Compute 1/sqrt(L_x).                                                |
 |       L_x is positive.                                                    |
 |                                                                           |
 |       if L_x is negative or zero, result is 1 (3fff ffff).                |
 |---------------------------------------------------------------------------|
 |  Algorithm:                                                               |
 |                                                                           |
 |   The function 1/sqrt(L_x) is approximated by a table and linear          |
 |   interpolation.                                                          |
 |                                                                           |
 |   1- Normalization of L_x.                                                |
 |   2- If (30-exponent) is even then shift right once.                      |
 |   3- exponent = (30-exponent)/2  +1                                       |
 |   4- i = bit25-b31 of L_x,    16 <= i <= 63  ->because of normalization.  |
 |   5- a = bit10-b24                                                        |
 |   6- i -=16                                                               |
 |   7- L_y = tabsqr[i]<<16 - (tabsqr[i] - tabsqr[i+1]) * a * 2                 |
 |   8- L_y >>= exponent                                                     |
 |___________________________________________________________________________|
*/


Word32 Inv_sqrt(   /* (o) Q30 : output value   (range: 0<=val<1)           */
  Word32 L_x       /* (i) Q0  : input value    (range: 0<=val<=7fffffff)   */
)
{
  Word16 exp, i, a, tmp;
  Word32 L_y;

  if( L_x <= (Word32)0) return ( (Word32)0x3fffffffL);

  exp = norm_l(L_x);
  L_x = L_shl(L_x, exp );               /* L_x is normalize */

  exp = sub(30, exp);
  if( (exp & 1) == 0 )                  /* If exponent even -> shift right */
      L_x = L_shr(L_x, 1);

  exp = shr(exp, 1);
  exp = add(exp, 1);

  L_x = L_shr(L_x, 9);
  i   = extract_h(L_x);                 /* Extract b25-b31 */
  L_x = L_shr(L_x, 1);
  a   = extract_l(L_x);                 /* Extract b10-b24 */
  a   = a & (Word16)0x7fff;

  i   = sub(i, 16);

  L_y = L_deposit_h(tabsqr[i]);         /* tabsqr[i] << 16          */
  tmp = sub(tabsqr[i], tabsqr[i+1]);    /* tabsqr[i] - tabsqr[i+1])  */
  L_y = L_msu(L_y, tmp, a);             /* L_y -=  tmp*a*2         */

  L_y = L_shr(L_y, exp);                /* denormalization */

  return(L_y);
}