mathhalf.c

GSM中半速率语音编解码源码

 *     Put the 16 bit input into the 16 MSB's of the output Longword.  The
 *     LS 16 bits are zeroed.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     L_Out
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff 0000.
 *
 *
 *   KEYWORDS: deposit, assign, fractional assign
 *
 *************************************************************************/

Longword L_deposit_h(Shortword var1)
{
  Longword L_var2;

  L_var2 = (Longword) var1 << 16;
  return (L_var2);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_deposit_l
 *
 *   PURPOSE:
 *
 *     Put the 16 bit input into the 16 LSB's of the output Longword with
 *     sign extension i.e. the top 16 bits are set to either 0 or 0xffff.
 *
 *   INPUTS:
 *
 *     var1
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var1 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     L_Out
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0xffff 8000 <= L_var1 <= 0x0000 7fff.
 *
 *   KEYWORDS: deposit, assign
 *
 *************************************************************************/

Longword L_deposit_l(Shortword var1)
{
  Longword L_Out;

  L_Out = var1;
  return (L_Out);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_mac
 *
 *   PURPOSE:
 *
 *     Multiply accumulate.  Fractionally multiply two 16 bit
 *     numbers together with saturation.  Add that result to the
 *     32 bit input with saturation.  Return the 32 bit result.
 *
 *   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.
 *     L_var3
 *                     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:
 *
 *     Fractionally multiply two 16 bit numbers together with
 *     saturation.  The only numbers which will cause saturation on
 *     the multiply are 0x8000 * 0x8000.
 *
 *     Add that result to the 32 bit input with saturation.
 *     Return the 32 bit result.
 *
 *     Please note that this is not a true multiply accumulate as
 *     most processors would implement it.  The 0x8000*0x8000
 *     causes and overflow for this instruction.  On most
 *     processors this would cause an overflow only if the 32 bit
 *     input added to it were positive or zero.
 *
 *   KEYWORDS: mac, multiply accumulate
 *
 *************************************************************************/

Longword L_mac(Longword L_var3, Shortword var1, Shortword var2)
{
  return (L_add(L_var3, L_mult(var1, var2)));
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_msu
 *
 *   PURPOSE:
 *
 *     Multiply and subtract.  Fractionally multiply two 16 bit
 *     numbers together with saturation.  Subtract that result from
 *     the 32 bit input with saturation.  Return the 32 bit result.
 *
 *   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.
 *     L_var3
 *                     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:
 *
 *     Fractionally multiply two 16 bit numbers together with
 *     saturation.  The only numbers which will cause saturation on
 *     the multiply are 0x8000 * 0x8000.
 *
 *     Subtract that result from the 32 bit input with saturation.
 *     Return the 32 bit result.
 *
 *     Please note that this is not a true multiply accumulate as
 *     most processors would implement it.  The 0x8000*0x8000
 *     causes and overflow for this instruction.  On most
 *     processors this would cause an overflow only if the 32 bit
 *     input added to it were negative or zero.
 *
 *   KEYWORDS: mac, multiply accumulate, msu
 *
 *************************************************************************/

Longword L_msu(Longword L_var3, Shortword var1, Shortword var2)
{
  return (L_sub(L_var3, L_mult(var1, var2)));
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_mult
 *
 *   PURPOSE:
 *
 *     Perform a fractional multipy of the two 16 bit input numbers
 *     with saturation.  Output a 32 bit number.
 *
 *   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:
 *
 *     L_Out
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *   IMPLEMENTATION:
 *
 *     Multiply the two the two 16 bit input numbers. If the
 *     result is within this range, left shift the result by one
 *     and output the 32 bit number.  The only possible overflow
 *     occurs when var1==var2==-0x8000.  In this case output
 *     0x7fff ffff.
 *
 *   KEYWORDS: multiply, mult, mpy
 *
 *************************************************************************/

Longword L_mult(Shortword var1, Shortword var2)
{
  Longword L_product;

  if (var1 == SW_MIN && var2 == SW_MIN)
    L_product = LW_MAX;                /* overflow */
  else
  {
    L_product = (Longword) var1 *var2; /* integer multiply */

    L_product = L_product << 1;
  }
  return (L_product);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_negate
 *
 *   PURPOSE:
 *
 *     Negate the 32 bit input. 0x8000 0000's negated value is
 *     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 0001 <= L_var1 <= 0x7fff ffff.
 *
 *   KEYWORDS: negate, negative
 *
 *************************************************************************/

Longword L_negate(Longword L_var1)
{
  Longword L_Out;

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

/***************************************************************************
 *
 *   FUNCTION NAME: L_shift_r
 *
 *   PURPOSE:
 *
 *     Shift and round.  Perform a shift right. After shifting, use
 *     the last bit shifted out of the LSB to round the result up
 *     or down.
 *
 *   INPUTS:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *
 *   OUTPUTS:
 *
 *     none
 *
 *   RETURN VALUE:
 *
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range
 *                     0x8000 0000 <= L_var1 <= 0x7fff ffff.
 *
 *
 *   IMPLEMENTATION:
 *
 *     Shift and round.  Perform a shift right. After shifting, use
 *     the last bit shifted out of the LSB to round the result up
 *     or down.  This is just like shift_r above except that the
 *     input/output is 32 bits as opposed to 16.
 *
 *     if var2 is positve perform a arithmetic left shift
 *     with saturation (see L_shl() above).
 *
 *     If var2 is zero simply return L_var1.
 *
 *     If var2 is negative perform a arithmetic right shift (L_shr)
 *     of L_var1 by (-var2)+1.  Add the LS bit of the result to
 *     L_var1 shifted right (L_shr) by -var2.
 *
 *     Note that there is no constraint on var2, so if var2 is
 *     -0xffff 8000 then -var2 is 0x0000 8000, not 0x0000 7fff.
 *     This is the reason the L_shl function is used.
 *
 *
 *   KEYWORDS:
 *
 *************************************************************************/

Longword L_shift_r(Longword L_var1, Shortword var2)
{
  Longword L_Out,
         L_rnd;

  if (var2 < -31)
  {
    L_Out = 0;
  }
  else if (var2 < 0)
  {
    /* right shift */
    L_rnd = L_shl(L_var1, var2 + 1) & 0x1;
    L_Out = L_add(L_shl(L_var1, var2), L_rnd);
  }
  else
    L_Out = L_shl(L_var1, var2);

  return (L_Out);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_shl
 *
 *   PURPOSE:
 *
 *     Arithmetic shift left (or right).
 *     Arithmetically shift the input left by var2.   If var2 is
 *     negative then an arithmetic shift right (L_shr) of L_var1 by
 *     -var2 is performed.
 *
 *   INPUTS:
 *
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *     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.
 *
 *
 *   IMPLEMENTATION:
 *
 *     Arithmetically shift the 32 bit input left by var2.  This
 *     operation maintains the sign of the input number. If var2 is
 *     negative then an arithmetic shift right (L_shr) of L_var1 by
 *     -var2 is performed.  See description of L_shr for details.
 *
 *     Equivalent to the Full-Rate GSM ">> n" operation.  Note that
 *     ANSI-C does not guarantee operation of the C ">>" or "<<"
 *     operator for negative numbers.
 *
 *   KEYWORDS: shift, arithmetic shift left,
 *
 *************************************************************************/

Longword L_shl(Longword L_var1, Shortword var2)
{

  Longword L_Mask,
         L_Out;
  int    i,
         iOverflow = 0;

  if (var2 == 0 || L_var1 == 0)
  {
    L_Out = L_var1;
  }
  else if (var2 < 0)
  {
    if (var2 <= -31)
    {
      if (L_var1 > 0)
        L_Out = 0;
      else
        L_Out = 0xffffffffL;
    }
    else
      L_Out = L_shr(L_var1, -var2);
  }
  else
  {

    if (var2 >= 31)
      iOverflow = 1;

    else
    {

      if (L_var1 < 0)
        L_Mask = LW_SIGN;              /* sign bit mask */
      else
        L_Mask = 0x0;
      L_Out = L_var1;
      for (i = 0; i < var2 && !iOverflow; i++)
      {
        /* check the sign bit */
        L_Out = (L_Out & 0x7fffffffL) << 1;
        if ((L_Mask ^ L_Out) & LW_SIGN)
          iOverflow = 1;
      }
    }

    if (iOverflow)
    {
      /* saturate */
      if (L_var1 > 0)
        L_Out = LW_MAX;
      else
        L_Out = LW_MIN;
    }
  }

  return (L_Out);
}

/***************************************************************************
 *
 *   FUNCTION NAME: L_shr
 *
 *   PURPOSE:
 *
 *     Arithmetic shift right (or left).
 *     Arithmetically shift the input right by var2.   If var2 is
 *     negative then an arithmetic shift left (shl) of var1 by
 *     -var2 is performed.
 *
 *   INPUTS:
 *
 *     var2
 *                     16 bit short signed integer (Shortword) whose value
 *                     falls in the range 0xffff 8000 <= var2 <= 0x0000 7fff.
 *     L_var1
 *                     32 bit long signed integer (Longword) whose value
 *                     falls in the range