reg_mul.c

linux 内核源代码

/*---------------------------------------------------------------------------+
 |  reg_mul.c                                                                |
 |                                                                           |
 | Multiply one FPU_REG by another, put the result in a destination FPU_REG. |
 |                                                                           |
 | Copyright (C) 1992,1993,1997                                              |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   [e-mail]                              |
 |                                                                           |
 | Returns the tag of the result if no exceptions or errors occurred.        |
 |                                                                           |
 +---------------------------------------------------------------------------*/

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

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


/*
  Multiply two registers to give a register result.
  The sources are st(deststnr) and (b,tagb,signb).
  The destination is st(deststnr).
  */
/* This routine must be called with non-empty source registers */
int FPU_mul(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
{
  FPU_REG *a = &st(deststnr);
  FPU_REG *dest = a;
  u_char taga = FPU_gettagi(deststnr);
  u_char saved_sign = getsign(dest);
  u_char sign = (getsign(a) ^ getsign(b));
  int tag;


  if ( !(taga | tagb) )
    {
      /* Both regs Valid, this should be the most common case. */

      tag = FPU_u_mul(a, b, dest, control_w, sign, exponent(a) + exponent(b));
      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);
      tag = FPU_u_mul(&x, &y, dest, control_w, sign,
		      exponent16(&x) + exponent16(&y));
      if ( tag < 0 )
	{
	  setsign(dest, saved_sign);
	  return tag;
	}
      FPU_settagi(deststnr, tag);
      return tag;
    }
  else if ( (taga <= TW_Denormal) && (tagb <= TW_Denormal) )
    {
      if ( ((tagb == TW_Denormal) || (taga == TW_Denormal))
	   && (denormal_operand() < 0) )
	return FPU_Exception;

      /* Must have either both arguments == zero, or
	 one valid and the other zero.
	 The result is therefore zero. */
      FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
      /* The 80486 book says that the answer is +0, but a real
	 80486 behaves this way.
	 IEEE-754 apparently says it should be this way. */
      setsign(dest, sign);
      return TAG_Zero;
    }
      /* Must have infinities, NaNs, etc */
  else if ( (taga == TW_NaN) || (tagb == TW_NaN) )
    {
      return real_2op_NaN(b, tagb, deststnr, &st(0));
    }
  else if ( ((taga == TW_Infinity) && (tagb == TAG_Zero))
	    || ((tagb == TW_Infinity) && (taga == TAG_Zero)) )
    {
      return arith_invalid(deststnr);  /* Zero*Infinity is invalid */
    }
  else if ( ((taga == TW_Denormal) || (tagb == TW_Denormal))
	    && (denormal_operand() < 0) )
    {
      return FPU_Exception;
    }
  else if (taga == TW_Infinity)
    {
      FPU_copy_to_regi(a, TAG_Special, deststnr);
      setsign(dest, sign);
      return TAG_Special;
    }
  else if (tagb == TW_Infinity)
    {
      FPU_copy_to_regi(b, TAG_Special, deststnr);
      setsign(dest, sign);
      return TAG_Special;
    }

#ifdef PARANOID
  else
    {
      EXCEPTION(EX_INTERNAL|0x102);
      return FPU_Exception;
    }
#endif /* PARANOID */ 

	return 0;
}