mathhalf.c

MSP430单片机C语言实例精讲

  Longword L_Mask,
         L_Out;

  if (var2 == 0 || L_var1 == 0) {
    L_Out = L_var1;
  }
  else if (var2 < 0) {
    /* perform a left shift */
    /*----------------------*/
      if (var2 <= -31) {
	  L_Out = (L_var1 > 0) ? LW_MAX : LW_MIN;   /* saturate */

      }   
    else
      L_Out = L_shl(L_var1, (Shortword)-var2);
  }
  else {

    if (var2 >= 31)
      L_Out = (L_var1 > 0) ? 0 : 0xffffffffL;
    else {
      L_Mask = 0;

      if (L_var1 < 0) {
        L_Mask = ~L_Mask << (32 - var2);
      }

      L_var1 >>= var2;
      L_Out = L_Mask | L_var1;
    }
  }
  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=0;
  int    i,
         iOverflow = 0;

  if (var2 == 0 || L_var1 == 0) {
    L_Out = L_var1;
  }
  else if (var2 < 0) {
    if (var2 <= -31)
      L_Out = (L_var1 > 0) ? 0 : 0xffffffffL;
    else
      L_Out = L_shr(L_var1, (Shortword)-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) {
	L_Out = (L_var1 > 0) ? LW_MAX : LW_MIN;   /* saturate */

    }   
  }


  return (L_Out);
}

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

    }
  }

  return (swOut);
}

/***************************************************************************
 *
 *   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 = (Longword)(L_shl(L_var1, (Shortword)(var2 + 1)) & (Longword)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: norm_l
 *
 *   PURPOSE:
 *
 *     Get normalize shift count:
 *
 *     A 32 bit number is input (possiblly unnormalized).  Output
 *     the positive (or zero) shift count required to normalize the
 *     input.
 *
 *   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
 *                     0 <= swOut <= 31
 *
 *
 *
 *   IMPLEMENTATION:
 *
 *     Get normalize shift count:
 *
 *     A 32 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 0000 >= normlzd number >= 0x7fff ffff (positive number)
 *     or
 *     0x8000 0000 <= normlzd number < 0xc000 0000 (negative number)
 *
 *     Return the number of shifts.
 *
 *     This instruction corresponds exactly to the Full-Rate "norm"
 *     instruction.
 *
 *   KEYWORDS: norm, normalization
 *
 *************************************************************************/

Shortword norm_l(Longword L_var1)
{

  Shortword swShiftCnt;

  if (L_var1 != 0) {
    if (!(L_var1 & LW_SIGN)) {

      /* positive input */
      for (swShiftCnt = 0; !(L_var1 <= LW_MAX && L_var1 >= 0x40000000L);
           swShiftCnt++) {
        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: 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
 *