mathdp31.c

2400bps MELP语音编解码源程序。

/*

2.4 kbps MELP Proposed Federal Standard speech coder

Fixed-point C code, version 1.0

Copyright (c) 1998, Texas Instruments, Inc.  

Texas Instruments has intellectual property rights on the MELP
algorithm.  The Texas Instruments contact for licensing issues for
commercial and non-government use is William Gordon, Director,
Government Contracts, Texas Instruments Incorporated, Semiconductor
Group (phone [phone]).

The fixed-point version of the voice codec Mixed Excitation Linear
Prediction (MELP) is based on specifications on the C-language software
simulation contained in GSM 06.06 which is protected by copyright and
is the property of the European Telecommunications Standards Institute
(ETSI). This standard is available from the ETSI publication office
tel. [phone]. ETSI has granted a license to United States
Department of Defense to use the C-language software simulation contained
in GSM 06.06 for the purposes of the development of a fixed-point
version of the voice codec Mixed Excitation Linear Prediction (MELP).
Requests for authorization to make other use of the GSM 06.06 or
otherwise distribute or modify them need to be addressed to the ETSI
Secretariat fax: [phone].

*/
/***************************************************************************
 *
 *   File Name:  mathdp31.c
 *
 *   Purpose:  Contains functions increased-precision arithmetic operations.
 *
 *      Below is a listing of all the functions in this file.  There
 *      is no interdependence among the functions.
 *
 *      L_mpy_ls()
 *      L_mpy_ll()
 *      isLwLimit()
 *      isSwLimit()
 *
 ***************************************************************************/
/*_________________________________________________________________________
 |                                                                         |
 |                              Include Files                              |
 |_________________________________________________________________________|
*/

#include "mathhalf.h"
#include "typedefs.h"

/****************************************************************************
 *
 *     FUNCTION NAME: isLwLimit
 *
 *     PURPOSE:
 *
 *        Check to see if the input Longword is at the
 *        upper or lower limit of its range.  i.e.
 *        0x7fff ffff or -0x8000 0000
 *
 *        Ostensibly this is a check for an overflow.
 *        This does not truly mean an overflow occurred,
 *        it means the value reached is the
 *        maximum/minimum value representable.  It may
 *        have come about due to an overflow.
 *
 *     INPUTS:
 *
 *       L_In               A Longword input variable
 *
 *
 *     OUTPUTS:             none
 *
 *     RETURN VALUE:        1 if input == 0x7fff ffff or -0x8000 0000
 *                          0 otherwise
 *
 *     KEYWORDS: saturation, limit
 *
 ***************************************************************************/

short  isLwLimit(Longword L_In)
{

  Longword L_ls;
  short  siOut;

  if (L_In != 0)
  {
    L_ls = L_shl(L_In, 1);
    if (L_sub(L_In, L_ls) == 0)
      siOut = 1;
    else
      siOut = 0;
  }
  else
  {
    siOut = 0;
  }
  return (siOut);
}

/****************************************************************************
 *
 *     FUNCTION NAME: isSwLimit
 *
 *     PURPOSE:
 *
 *        Check to see if the input Shortword is at the
 *        upper or lower limit of its range.  i.e.
 *        0x7fff or -0x8000
 *
 *        Ostensibly this is a check for an overflow.
 *        This does not truly mean an overflow occurred,
 *        it means the value reached is the
 *        maximum/minimum value representable.  It may
 *        have come about due to an overflow.
 *
 *     INPUTS:
 *
 *       swIn               A Shortword input variable
 *
 *
 *     OUTPUTS:             none
 *
 *     RETURN VALUE:        1 if input == 0x7fff or -0x8000
 *                          0 otherwise
 *
 *     KEYWORDS: saturation, limit
 *
 ***************************************************************************/

short  isSwLimit(Shortword swIn)
{

  Shortword swls;
  short  siOut;

  if (swIn != 0)
  {
    swls = shl(swIn, 1);
    if (sub(swIn, swls) == 0)          /* logical compare outputs 1/0 */
      siOut = 1;
    else
      siOut = 0;
  }
  else
  {
    siOut = 0;
  }
  return (siOut);

}

/****************************************************************************
 *
 *     FUNCTION NAME: L_mpy_ll
 *
 *     PURPOSE:    Multiply a 32 bit number (L_var1) and a 32 bit number
 *                 (L_var2), and return a 32 bit result.
 *
 *     INPUTS:
 *
 *       L_var1             A Longword input variable
 *
 *       L_var2             A Longword input variable
 *
 *     OUTPUTS:             none
 *
 *     IMPLEMENTATION:
 *
 *        Performs a 31x31 bit multiply, Complexity=24 Ops.
 *
 *        Let x1x0, or y1y0, be the two constituent halves
 *        of a 32 bit number.  This function performs the
 *        following:
 *
 *        low = ((x0 >> 1)*(y0 >> 1)) >> 16     (low * low)
 *        mid1 = [(x1 * (y0 >> 1)) >> 1 ]       (high * low)
 *        mid2 = [(y1 * (x0 >> 1)) >> 1]        (high * low)
 *        mid =  (mid1 + low + mid2) >> 14      (sum so far)
 *        output = (y1*x1) + mid                (high * high)
 *
 *
 *     RETURN VALUE:        A Longword value
 *
 *     KEYWORDS: mult,mpy,multiplication
 *
 ***************************************************************************/

Longword L_mpy_ll(Longword L_var1, Longword L_var2)
{
  Shortword swLow1,
         swLow2,
         swHigh1,
         swHigh2;
  Longword L_varOut,
         L_low,
         L_mid1,
         L_mid2,
         L_mid;


  swLow1 = shr(extract_l(L_var1), 1);
  swLow1 = SW_MAX & swLow1;

  swLow2 = shr(extract_l(L_var2), 1);
  swLow2 = SW_MAX & swLow2;
  swHigh1 = extract_h(L_var1);
  swHigh2 = extract_h(L_var2);

  L_low = L_mult(swLow1, swLow2);
  L_low = L_shr(L_low, 16);

  L_mid1 = L_mult(swHigh1, swLow2);
  L_mid1 = L_shr(L_mid1, 1);
  L_mid = L_add(L_mid1, L_low);

  L_mid2 = L_mult(swHigh2, swLow1);
  L_mid2 = L_shr(L_mid2, 1);
  L_mid = L_add(L_mid, L_mid2);

  L_mid = L_shr(L_mid, 14);
  L_varOut = L_mac(L_mid, swHigh1, swHigh2);

  return (L_varOut);
}

/****************************************************************************
 *
 *     FUNCTION NAME: L_mpy_ls
 *
 *     PURPOSE:    Multiply a 32 bit number (L_var2) and a 16 bit
 *                 number (var1) returning a 32 bit result. L_var2
 *                 is truncated to 31 bits prior to executing the
 *                 multiply.
 *
 *     INPUTS:
 *
 *       L_var2             A Longword input variable
 *
 *       var1               A Shortword input variable
 *
 *     OUTPUTS:             none
 *
 *     RETURN VALUE:        A Longword value
 *
 *     KEYWORDS: mult,mpy,multiplication
 *
 ***************************************************************************/

Longword L_mpy_ls(Longword L_var2, Shortword var1)
{
  Longword L_varOut;
  Shortword swtemp;

  swtemp = shr(extract_l(L_var2), 1);
  swtemp = (short) 32767 & (short) swtemp;

  L_varOut = L_mult(var1, swtemp);
  L_varOut = L_shr(L_varOut, 15);
  L_varOut = L_mac(L_varOut, var1, extract_h(L_var2));
  return (L_varOut);
}