mathhalf.c

GSM中半速率语音编解码源码

/***************************************************************************
 *
 *   File Name:  mathhalf.c
 *
 *   Purpose:  Contains functions which implement the primitive
 *     arithmetic operations.
 *
 *      The functions in this file are listed below.  Some of them are
 *      defined in terms of other basic operations.  One of the
 *      routines, saturate() is static.  This is not a basic
 *      operation, and is not referenced outside the scope of this
 *      file.
 *
 *
 *       abs_s()
 *       add()
 *       divide_s()
 *       extract_h()
 *       extract_l()
 *       L_abs()
 *       L_add()
 *       L_deposit_h()
 *       L_deposit_l()
 *       L_mac()
 *       L_msu()
 *       L_mult()
 *       L_negate()
 *       L_shift_r()
 *       L_shl()
 *       L_shr()
 *       L_sub()
 *       mac_r()
 *       msu_r()
 *       mult()
 *       mult_r()
 *       negate()
 *       norm_l()
 *       norm_s()
 *       round()
 *       saturate()
 *       shift_r()
 *       shl()
 *       shr()
 *       sub()
 *
 **************************************************************************/

/*_________________________________________________________________________
 |                                                                         |
 |                            Include Files                                |
 |_________________________________________________________________________|
*/

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

/***************************************************************************
 *
 *   FUNCTION NAME: saturate
 *
 *   PURPOSE:
 *
 *     Limit the 32 bit input to the range of a 16 bit word.
 *
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   KEYWORDS: saturation, limiting, limit, saturate, 16 bits
 *
 *************************************************************************/

static Shortword saturate(Longword L_var1)
{
  Shortword swOut;

  if (L_var1 > SW_MAX)
  {
    swOut = SW_MAX;
  }
  else if (L_var1 < SW_MIN)
  {
    swOut = SW_MIN;
  }
  else
    swOut = (Shortword) L_var1;        /* automatic type conversion */
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: abs_s
 *
 *   PURPOSE:
 *
 *     Take the absolute value of the 16 bit input.  An input of
 *     -0x8000 results in a return value of 0x7fff.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0x0000 0000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     Take the absolute value of the 16 bit input.  An input of
 *     -0x8000 results in a return value of 0x7fff.
 *
 *   KEYWORDS: absolute value, abs
 *
 *************************************************************************/

Shortword abs_s(Shortword var1)
{
  Shortword swOut;

  if (var1 == SW_MIN)
  {
    swOut = SW_MAX;
  }
  else
  {
    if (var1 < 0)
      swOut = -var1;
    else
      swOut = var1;
  }
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: add
 *
 *   PURPOSE:
 *
 *     Perform the addition of the two 16 bit input variable with
 *     saturation.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     Perform the addition of the two 16 bit input variable with
 *     saturation.
 *
 *     swOut = var1 + var2
 *
 *     swOut is set to 0x7fff if the operation results in an
 *     overflow.  swOut is set to 0x8000 if the operation results
 *     in an underflow.
 *
 *   KEYWORDS: add, addition
 *
 *************************************************************************/

Shortword add(Shortword var1, Shortword var2)
{
  Longword L_sum;
  Shortword swOut;

  L_sum = (Longword) var1 + var2;
  swOut = saturate(L_sum);
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: divide_s
 *
 *   PURPOSE:
 *
 *     Divide var1 by var2.  Note that both must be positive, and
 *     var1 >=  var2.  The output is set to 0 if invalid input is
 *     provided.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *     In the case where var1==var2 the function returns 0x7fff.  The output
 *     is undefined for invalid inputs.  This implementation returns zero
 *     and issues a warning via stdio if invalid input is presented.
 *
 *   KEYWORDS: divide
 *
 *************************************************************************/

Shortword divide_s(Shortword var1, Shortword var2)
{
  Longword L_div;
  Shortword swOut;

  if (var1 < 0 || var2 < 0 || var1 > var2)
  {
    /* undefined output for invalid input into divide_s */
    return (0);
  }

  if (var1 == var2)
    return (0x7fff);

  L_div = ((0x00008000L * (Longword) var1) / (Longword) var2);
  swOut = saturate(L_div);
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: extract_h
 *
 *   PURPOSE:
 *
 *     Extract the 16 MS bits of a 32 bit Longword.  Return the 16 bit
 *     number as a Shortword.  This is used as a "truncation" of a fractional
 *     number.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *   IMPLEMENTATION:
 *
 *   KEYWORDS: assign, truncate
 *
 *************************************************************************/

Shortword extract_h(Longword L_var1)
{
  Shortword var2;

  var2 = (Shortword) (0x0000ffffL & (L_var1 >> 16));
  return (var2);
}

/***************************************************************************
 *
 *   FUNCTION NAME: extract_l
 *
 *   PURPOSE:
 *
 *     Extract the 16 LS bits of a 32 bit Longword.  Return the 16 bit
 *     number as a Shortword.  The upper portion of the input Longword
 *     has no impact whatsoever on the output.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     swOut
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= swOut <= 0x0000 7fff.
 *
 *
 *   KEYWORDS: extract, assign
 *
 *************************************************************************/

Shortword extract_l(Longword L_var1)
{
  Shortword var2;

  var2 = (Shortword) (0x0000ffffL & L_var1);
  return (var2);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_abs
 *
 *   PURPOSE:
 *
 *     Take the absolute value of the 32 bit input.  An input of
 *     -0x8000 0000 results in a return value of 0x7fff ffff.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     L_Out
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *
 *
 *   KEYWORDS: absolute value, abs
 *
 *************************************************************************/
Longword L_abs(Longword L_var1)
{
  Longword L_Out;

  if (L_var1 == LW_MIN)
  {
    L_Out = LW_MAX;
  }
  else
  {
    if (L_var1 < 0)
      L_Out = -L_var1;
    else
      L_Out = L_var1;
  }
  return (L_Out);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_add
 *
 *   PURPOSE:
 *
 *     Perform the addition of the two 32 bit input variables with
 *     saturation.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *     L_var2
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var2 <= 0x7fff ffff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     L_Out
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   IMPLEMENTATION:
 *
 *     Perform the addition of the two 32 bit input variables with
 *     saturation.
 *
 *     L_Out = L_var1 + L_var2
 *
 *     L_Out is set to 0x7fff ffff if the operation results in an
 *     overflow.  L_Out is set to 0x8000 0000 if the operation
 *     results in an underflow.
 *
 *   KEYWORDS: add, addition
 *
 *************************************************************************/
Longword L_add(Longword L_var1, Longword L_var2)
{

  Longword L_Sum,
         L_SumLow,
         L_SumHigh;

  L_Sum = L_var1 + L_var2;

  if ((L_var1 > 0 && L_var2 > 0) || (L_var1 < 0 && L_var2 < 0))
  {

    /* an overflow is possible */

    L_SumLow = (L_var1 & 0xffff) + (L_var2 & 0xffff);
    L_SumHigh = ((L_var1 >> 16) & 0xffff) + ((L_var2 >> 16) & 0xffff);
    if (L_SumLow & 0x10000)
    {
      /* carry into high word is set */
      L_SumHigh += 1;
    }

    /* update sum only if there is an overflow or underflow */
    /*------------------------------------------------------*/

    if ((0x10000 & L_SumHigh) && !(0x8000 & L_SumHigh))
      L_Sum = LW_MIN;                  /* underflow */
    else if (!(0x10000 & L_SumHigh) && (0x8000 & L_SumHigh))
      L_Sum = LW_MAX;                  /* overflow */
  }

  return (L_Sum);

}

/***************************************************************************
 *
 *   FUNCTION NAME: L_deposit_h
 *
 *   PURPOSE:
 *