Bochs/bochs/fpu/reg_add_sub.c

/*---------------------------------------------------------------------------+
 |  reg_add_sub.c                                                            |
 |                                                                           |
 | Functions to add or subtract two registers and put the result in a third. |
 |                                                                           |
 | Copyright (C) 1992,1993,1997                                              |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   billm@suburbia.net                              |
 |                                                                           |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 |  For each function, the destination may be any FPU_REG, including one of  |
 | the source FPU_REGs.                                                      |
 |  Each function returns 0 if the answer is o.k., otherwise a non-zero      |
 | value is returned, indicating either an exception condition or an         |
 | internal error.                                                           |
 +---------------------------------------------------------------------------*/

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

static
int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
		     FPU_REG const *b, u_char tagb, u_char signb,
		     FPU_REG *dest, int deststnr, u16 control_w);

/*
  Operates on st(0) and st(n), or on st(0) and temporary data.
  The destination must be one of the source st(x).
  */
int FPU_add(FPU_REG const *b, u_char tagb, int deststnr, u16 control_w)
{
  FPU_REG *a = &st(0);
  FPU_REG *dest = &st(deststnr);
  u_char signb = getsign(b);
  u_char taga = FPU_gettag0();
  u_char signa = getsign(a);
  u_char saved_sign = getsign(dest);
  int diff, tag, expa, expb;
  
  if ( !(taga | tagb) )
    {
      expa = exponent(a);
      expb = exponent(b);

    valid_add:
      /* Both registers are valid */
      if (!(signa ^ signb))
	{
	  /* signs are the same */
	  tag = FPU_u_add(a, b, dest, control_w, signa, expa, expb);
	}
      else
	{
	  /* The signs are different, so do a subtraction */
	  diff = expa - expb;
	  if (!diff)
	    {
	      diff = a->sigh - b->sigh;  /* This works only if the ms bits
					    are identical. */
	      if (!diff)
		{
		  diff = a->sigl > b->sigl;
		  if (!diff)
		    diff = -(a->sigl < b->sigl);
		}
	    }
      
	  if (diff > 0)
	    {
	      tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
	    }
	  else if ( diff < 0 )
	    {
	      tag = FPU_u_sub(b, a, dest, control_w, signb, expb, expa);
	    }
	  else
	    {
	      FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
	      /* sign depends upon rounding mode */
	      setsign(dest, ((control_w & CW_RC) != RC_DOWN)
		      ? SIGN_POS : SIGN_NEG);
	      return TAG_Zero;
	    }
	}

      if ( tag < 0 )
	{
	  setsign(dest, saved_sign);
	  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)) )
    {
      FPU_REG x, y;

      if ( denormal_operand() < 0 )
	return FPU_Exception;

      FPU_to_exp16(a, &x);
      FPU_to_exp16(b, &y);
      a = &x;
      b = &y;
      expa = exponent16(a);
      expb = exponent16(b);
      goto valid_add;
    }

  if ( (taga == TW_NaN) || (tagb == TW_NaN) )
    {
      if ( deststnr == 0 )
	return real_2op_NaN(b, tagb, deststnr, a);
      else
	return real_2op_NaN(a, taga, deststnr, a);
    }

  return add_sub_specials(a, taga, signa, b, tagb, signb,
			  dest, deststnr, control_w);
}


/* Subtract b from a.  (a-b) -> dest
 bbd: arg2 used to be int type, but sometimes pointers were forced
 in with typecasts.  On Alphas pointers are 64 bits and ints are 32,
 so when rm was cast back to a pointer...SEGFAULT.  Pass the pointers
 around instead, since they are always larger precision than the
 register numbers. */
int FPU_sub(int flags, FPU_REG *rm, u16 control_w)
{
  FPU_REG const *a, *b;
  FPU_REG *dest;
  u_char taga, tagb, signa, signb, saved_sign, sign;
  int diff, tag, expa, expb, deststnr;

  a = &st(0);
  taga = FPU_gettag0();

  deststnr = 0;
  if ( flags & LOADED )
    {
      b = rm;
      tagb = flags & 0x0f;
    }
  else
    {
      int rmint = PTR2INT(rm);
      b = &st(rmint);
      tagb = FPU_gettagi(rmint);

      if ( flags & DEST_RM )
	deststnr = rmint;
    }

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

  if ( flags & REV )
    {
      signa ^= SIGN_NEG;
      signb ^= SIGN_NEG;
    }

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

  if ( !(taga | tagb) )
    {
      expa = exponent(a);
      expb = exponent(b);

    valid_subtract:
      /* Both registers are valid */

      diff = expa - expb;

      if (!diff)
	{
	  diff = a->sigh - b->sigh;  /* Works only if ms bits are identical */
	  if (!diff)
	    {
	      diff = a->sigl > b->sigl;
	      if (!diff)
		diff = -(a->sigl < b->sigl);
	    }
	}

      switch ( (((int)signa)*2 + signb) / SIGN_NEG )
	{
	case 0: /* P - P */
	case 3: /* N - N */
	  if (diff > 0)
	    {
	      /* |a| > |b| */
	      tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
	    }
	  else if ( diff == 0 )
	    {
	      FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);

	      /* sign depends upon rounding mode */
	      setsign(dest, ((control_w & CW_RC) != RC_DOWN)
		? SIGN_POS : SIGN_NEG);
	      return TAG_Zero;
	    }
	  else
	    {
	      sign = signa ^ SIGN_NEG;
	      tag = FPU_u_sub(b, a, dest, control_w, sign, expb, expa);
	    }
	  break;
	case 1: /* P - N */
	  tag = FPU_u_add(a, b, dest, control_w, SIGN_POS, expa, expb);
	  break;
	case 2: /* N - P */
	  tag = FPU_u_add(a, b, dest, control_w, SIGN_NEG, expa, expb);
	  break;
#ifdef PARANOID
	default:
	  EXCEPTION(EX_INTERNAL|0x111);
	  return -1;
#endif
	}
      if ( tag < 0 )
	{
	  setsign(dest, saved_sign);
	  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)) )
    {
      FPU_REG x, y;

      if ( denormal_operand() < 0 )
	return FPU_Exception;

      FPU_to_exp16(a, &x);
      FPU_to_exp16(b, &y);
      a = &x;
      b = &y;
      expa = exponent16(a);
      expb = exponent16(b);

      goto valid_subtract;
    }

  if ( (taga == TW_NaN) || (tagb == TW_NaN) )
    {
      FPU_REG const *d1, *d2;
      if ( flags & REV )
	{
	  d1 = b;
	  d2 = a;
	}
      else
	{
	  d1 = a;
	  d2 = b;
	}
      if ( flags & LOADED )
	return real_2op_NaN(b, tagb, deststnr, d1);
      if ( flags & DEST_RM )
	return real_2op_NaN(a, taga, deststnr, d2);
      else
	return real_2op_NaN(b, tagb, deststnr, d2);
    }

    return add_sub_specials(a, taga, signa, b, tagb, signb ^ SIGN_NEG,
			    dest, deststnr, control_w);
}


static
int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
		     FPU_REG const *b, u_char tagb, u_char signb,
		     FPU_REG *dest, int deststnr, u16 control_w)
{
  if ( ((taga == TW_Denormal) || (tagb == TW_Denormal))
       && (denormal_operand() < 0) )
    return FPU_Exception;

  if (taga == TAG_Zero)
    {
      if (tagb == TAG_Zero)
	{
	  /* Both are zero, result will be zero. */
	  u_char different_signs = signa ^ signb;

	  FPU_copy_to_regi(a, TAG_Zero, deststnr);
	  if ( different_signs )
	    {
	      /* Signs are different. */
	      /* Sign of answer depends upon rounding mode. */
	      setsign(dest, ((control_w & CW_RC) != RC_DOWN)
		      ? SIGN_POS : SIGN_NEG);
	    }
	  else
	    setsign(dest, signa);  /* signa may differ from the sign of a. */
	  return TAG_Zero;
	}
      else
	{
	  reg_copy(b, dest);
	  if ( (tagb == TW_Denormal) && (b->sigh & 0x80000000) )
	    {
	      /* A pseudoDenormal, convert it. */
	      addexponent(dest, 1);
	      tagb = TAG_Valid;
	    }
	  else if ( tagb > TAG_Empty )
	    tagb = TAG_Special;
	  setsign(dest, signb);  /* signb may differ from the sign of b. */
	  FPU_settagi(deststnr, tagb);
	  return tagb;
	}
    }
  else if (tagb == TAG_Zero)
    {
      reg_copy(a, dest);
      if ( (taga == TW_Denormal) && (a->sigh & 0x80000000) )
	{
	  /* A pseudoDenormal */
	  addexponent(dest, 1);
	  taga = TAG_Valid;
	}
      else if ( taga > TAG_Empty )
	taga = TAG_Special;
      setsign(dest, signa);  /* signa may differ from the sign of a. */
      FPU_settagi(deststnr, taga);
      return taga;
    }
  else if (taga == TW_Infinity)
    {
      if ( (tagb != TW_Infinity) || (signa == signb) )
	{
	  FPU_copy_to_regi(a, TAG_Special, deststnr);
	  setsign(dest, signa);  /* signa may differ from the sign of a. */
	  return taga;
	}
      /* Infinity-Infinity is undefined. */
      return arith_invalid(deststnr);
    }
  else if (tagb == TW_Infinity)
    {
      FPU_copy_to_regi(b, TAG_Special, deststnr);
      setsign(dest, signb);  /* signb may differ from the sign of b. */
      return tagb;
    }

#ifdef PARANOID
  EXCEPTION(EX_INTERNAL|0x101);
#endif

  return FPU_Exception;
}