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reg_divide.c

/*---------------------------------------------------------------------------+
 |  reg_divide.c                                                             |
 |                                                                           |
 | Divide one FPU_REG by another and put the result in a destination FPU_REG.|
 |                                                                           |
 | Copyright (C) 1996                                                        |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   billm@jacobi.maths.monash.edu.au                |
 |                                                                           |
 |    Return value is the tag of the answer, or-ed with FPU_Exception if     |
 |    one was raised, or -1 on internal error.                               |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 | The destination may be any FPU_REG, including one of the source FPU_REGs. |
 +---------------------------------------------------------------------------*/

#include "exception.h"
#include "reg_constant.h"
#include "fpu_emu.h"
#include "fpu_system.h"

/*
  Divide one register by another and put the result into a third register.
  */
int FPU_div(int flags, int rm, int control_w)
{
  FPU_REG x, y;
  FPU_REG const *a, *b, *st0_ptr, *st_ptr;
  FPU_REG *dest;
  u_char taga, tagb, signa, signb, sign, saved_sign;
  int tag, deststnr;

  if ( flags & DEST_RM )
    deststnr = rm;
  else
    deststnr = 0;

  if ( flags & REV )
    {
      b = &st(0);
      st0_ptr = b;
      tagb = FPU_gettag0();
      if ( flags & LOADED )
      {
        a = (FPU_REG *)rm;
        taga = flags & 0x0f;
      }
      else
      {
        a = &st(rm);
        st_ptr = a;
        taga = FPU_gettagi(rm);
      }
    }
  else
    {
      a = &st(0);
      st0_ptr = a;
      taga = FPU_gettag0();
      if ( flags & LOADED )
      {
        b = (FPU_REG *)rm;
        tagb = flags & 0x0f;
      }
      else
      {
        b = &st(rm);
        st_ptr = b;
        tagb = FPU_gettagi(rm);
      }
    }

  signa = getsign(a);
  signb = getsign(b);

  sign = signa ^ signb;

  dest = &st(deststnr);
  saved_sign = getsign(dest);

  if ( !(taga | tagb) )
    {
      /* Both regs Valid, this should be the most common case. */
      reg_copy(a, &x);
      reg_copy(b, &y);
      setpositive(&x);
      setpositive(&y);
      tag = FPU_u_div(&x, &y, dest, control_w, sign);

      if ( tag < 0 )
      return tag;

      FPU_settagi(deststnr, tag);
      return tag;
    }

  if ( taga == TAG_Special )
    taga = FPU_Special(a);
  if ( tagb == TAG_Special )
    tagb = FPU_Special(b);

  if ( ((taga == TAG_Valid) && (tagb == TW_Denormal))
          || ((taga == TW_Denormal) && (tagb == TAG_Valid))
          || ((taga == TW_Denormal) && (tagb == TW_Denormal)) )
    {
      if ( denormal_operand() < 0 )
      return FPU_Exception;

      FPU_to_exp16(a, &x);
      FPU_to_exp16(b, &y);
      tag = FPU_u_div(&x, &y, dest, control_w, sign);
      if ( tag < 0 )
      return tag;

      FPU_settagi(deststnr, tag);
      return tag;
    }
  else if ( (taga <= TW_Denormal) && (tagb <= TW_Denormal) )
    {
      if ( tagb != TAG_Zero )
      {
        /* Want to find Zero/Valid */
        if ( tagb == TW_Denormal )
          {
            if ( denormal_operand() < 0 )
            return FPU_Exception;
          }

        /* The result is zero. */
        FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
        setsign(dest, sign);
        return TAG_Zero;
      }
      /* We have an exception condition, either 0/0 or Valid/Zero. */
      if ( taga == TAG_Zero )
      {
        /* 0/0 */
        return arith_invalid(deststnr);
      }
      /* Valid/Zero */
      return FPU_divide_by_zero(deststnr, sign);
    }
  /* Must have infinities, NaNs, etc */
  else if ( (taga == TW_NaN) || (tagb == TW_NaN) )
    {
      if ( flags & LOADED )
      return real_2op_NaN((FPU_REG *)rm, flags & 0x0f, 0, st0_ptr);

      if ( flags & DEST_RM )
      {
        int tag;
        tag = FPU_gettag0();
        if ( tag == TAG_Special )
          tag = FPU_Special(st0_ptr);
        return real_2op_NaN(st0_ptr, tag, rm, (flags & REV) ? st0_ptr : &st(rm));
      }
      else
      {
        int tag;
        tag = FPU_gettagi(rm);
        if ( tag == TAG_Special )
          tag = FPU_Special(&st(rm));
        return real_2op_NaN(&st(rm), tag, 0, (flags & REV) ? st0_ptr : &st(rm));
      }
    }
  else if (taga == TW_Infinity)
    {
      if (tagb == TW_Infinity)
      {
        /* infinity/infinity */
        return arith_invalid(deststnr);
      }
      else
      {
        /* tagb must be Valid or Zero */
        if ( (tagb == TW_Denormal) && (denormal_operand() < 0) )
          return FPU_Exception;
        
        /* Infinity divided by Zero or Valid does
           not raise and exception, but returns Infinity */
        FPU_copy_to_regi(a, TAG_Special, deststnr);
        setsign(dest, sign);
        return taga;
      }
    }
  else if (tagb == TW_Infinity)
    {
      if ( (taga == TW_Denormal) && (denormal_operand() < 0) )
      return FPU_Exception;

      /* The result is zero. */
      FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
      setsign(dest, sign);
      return TAG_Zero;
    }
#ifdef PARANOID
  else
    {
      EXCEPTION(EX_INTERNAL|0x102);
      return FPU_Exception;
    }
#endif /* PARANOID */ 

      return 0;
}

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