mathhalf.c

GSM中半速率语音编解码源码

      {
        L_var1 = L_var1 << 1;
      }

    }
    else
    {
      /* negative input */
      for (swShiftCnt = 0;
           !(L_var1 >= LW_MIN && L_var1 < (Longword) 0xc0000000L);
           swShiftCnt++)
      {
        L_var1 = L_var1 << 1;
      }
    }
  }
  else
  {
    swShiftCnt = 0;
  }
  return (swShiftCnt);
}

/***************************************************************************
 *
 *   FUNCTION NAME: norm_s
 *
 *   PURPOSE:
 *
 *     Get normalize shift count:
 *
 *     A 16 bit number is input (possiblly unnormalized).  Output
 *     the positive (or zero) shift count required to normalize the
 *     input.
 *
 *   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
 *                     0 <= swOut <= 15
 *
 *
 *
 *   IMPLEMENTATION:
 *
 *     Get normalize shift count:
 *
 *     A 16 bit number is input (possiblly unnormalized).  Output
 *     the positive (or zero) shift count required to normalize the
 *     input.
 *
 *     If zero in input, return 0 as the shift count.
 *
 *     For non-zero numbers, count the number of left shift
 *     required to get the number to fall into the range:
 *
 *     0x4000 >= normlzd number >= 0x7fff (positive number)
 *     or
 *     0x8000 <= normlzd number <  0xc000 (negative number)
 *
 *     Return the number of shifts.
 *
 *     This instruction corresponds exactly to the Full-Rate "norm"
 *     instruction.
 *
 *   KEYWORDS: norm, normalization
 *
 *************************************************************************/

Shortword norm_s(Shortword var1)
{

  short  swShiftCnt;
  Longword L_var1;

  L_var1 = L_deposit_h(var1);
  swShiftCnt = norm_l(L_var1);
  return (swShiftCnt);
}

/***************************************************************************
 *
 *   FUNCTION NAME: round
 *
 *   PURPOSE:
 *
 *     Round the 32 bit Longword into a 16 bit shortword with saturation.
 *
 *   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:
 *
 *     Perform a two's complement round on the input Longword with
 *     saturation.
 *
 *     This is equivalent to adding 0x0000 8000 to the input.  The
 *     result may overflow due to the add.  If so, the result is
 *     saturated.  The 32 bit rounded number is then shifted down
 *     16 bits and returned as a Shortword.
 *
 *
 *   KEYWORDS: round
 *
 *************************************************************************/

Shortword round(Longword L_var1)
{
  Longword L_Prod;

  L_Prod = L_add(L_var1, 0x00008000L); /* round MSP */
  return (extract_h(L_Prod));
}

/***************************************************************************
 *
 *   FUNCTION NAME: 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:
 *
 *     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:
 *
 *     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.
 *
 *     If var2 is positive perform a arithmetic left shift
 *     with saturation (see shl() above).
 *
 *     If var2 is zero simply return var1.
 *
 *     If var2 is negative perform a arithmetic right shift (shr)
 *     of var1 by (-var2)+1.  Add the LS bit of the result to var1
 *     shifted right (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 shl function is used.
 *
 *
 *   KEYWORDS:
 *
 *************************************************************************/

Shortword shift_r(Shortword var1, Shortword var2)
{
  Shortword swOut,
         swRnd;

  if (var2 >= 0)
    swOut = shl(var1, var2);
  else
  {

    /* right shift */

    if (var2 < -15)
    {

      swOut = 0;

    }
    else
    {

      swRnd = shl(var1, var2 + 1) & 0x1;
      swOut = add(shl(var1, var2), swRnd);

    }
  }
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: shl
 *
 *   PURPOSE:
 *
 *     Arithmetically shift the input left by var2.
 *
 *
 *   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:
 *
 *     If Arithmetically shift the input left by var2.  If var2 is
 *     negative then an arithmetic shift right (shr) of var1 by
 *     -var2 is performed.  See description of shr for details.
 *     When an arithmetic shift left is performed the var2 LS bits
 *     are zero filled.
 *
 *     The only exception is if the left shift causes an overflow
 *     or underflow.  In this case the LS bits are not modified.
 *     The number returned is 0x8000 in the case of an underflow or
 *     0x7fff in the case of an overflow.
 *
 *     The shl is equivalent to the Full-Rate GSM "<< n" operation.
 *     Note that ANSI-C does not guarantee operation of the C ">>"
 *     or "<<" operator for negative numbers - it is not specified
 *     whether this shift is an arithmetic or logical shift.
 *
 *   KEYWORDS: asl, arithmetic shift left, shift
 *
 *************************************************************************/

Shortword shl(Shortword var1, Shortword var2)
{
  Shortword swOut;
  Longword L_Out;

  if (var2 == 0 || var1 == 0)
  {
    swOut = var1;
  }
  else if (var2 < 0)
  {

    /* perform a right shift */
    /*-----------------------*/

    if (var2 <= -15)
    {
      if (var1 < 0)
        swOut = (Shortword) 0xffff;
      else
        swOut = 0x0;
    }
    else
      swOut = shr(var1, -var2);

  }
  else
  {
    /* var2 > 0 */
    if (var2 >= 15)
    {
      /* saturate */
      if (var1 > 0)
        swOut = SW_MAX;
      else
        swOut = SW_MIN;
    }
    else
    {

      L_Out = (Longword) var1 *(1 << var2);

      swOut = (Shortword) L_Out;       /* copy low portion to swOut, overflow
                                        * could have hpnd */
      if (swOut != L_Out)
      {
        /* overflow  */
        if (var1 > 0)
          swOut = SW_MAX;              /* saturate */
        else
          swOut = SW_MIN;              /* saturate */
      }
    }
  }
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: 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:
 *
 *     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:
 *
 *     Arithmetically shift the input right by var2.  This
 *     operation maintains the sign of the input number. If var2 is
 *     negative then an arithmetic shift left (shl) of var1 by
 *     -var2 is performed.  See description of shl 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 right,
 *
 *************************************************************************/

Shortword shr(Shortword var1, Shortword var2)
{

  Shortword swMask,
         swOut;

  if (var2 == 0 || var1 == 0)
    swOut = var1;

  else if (var2 < 0)
  {
    /* perform an arithmetic left shift */
    /*----------------------------------*/
    if (var2 <= -15)
    {
      /* saturate */
      if (var1 > 0)
        swOut = SW_MAX;
      else
        swOut = SW_MIN;
    }
    else
      swOut = shl(var1, -var2);
  }

  else
  {

    /* positive shift count */
    /*----------------------*/

    if (var2 >= 15)
    {
      if (var1 < 0)
        swOut = (Shortword) 0xffff;
      else
        swOut = 0x0;
    }
    else
    {
      /* take care of sign extension */
      /*-----------------------------*/

      swMask = 0;
      if (var1 < 0)
      {
        swMask = ~swMask << (16 - var2);
      }

      var1 >>= var2;
      swOut = swMask | var1;

    }
  }
  return (swOut);
}

/***************************************************************************
 *
 *   FUNCTION NAME: sub
 *
 *   PURPOSE:
 *
 *     Perform the subtraction 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 subtraction 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: sub, subtraction
 *
 *************************************************************************/
Shortword sub(Shortword var1, Shortword var2)
{
  Longword L_diff;
  Shortword swOut;

  L_diff = (Longword) var1 - var2;
  swOut = saturate(L_diff);

  return (swOut);
}