arch/parisc/math-emu/dfsub.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * Linux/PA-RISC Project (http://www.parisc-linux.org/)
  *
  * Floating-point emulation code
  *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
  */
 /*
  * BEGIN_DESC
  *
  *  File:
  *	@(#)	pa/spmath/dfsub.c		$Revision: 1.1 $
  *
  *  Purpose:
  *	Double_subtract: subtract two double precision values.
  *
  *  External Interfaces:
  *	dbl_fsub(leftptr, rightptr, dstptr, status)
  *
  *  Internal Interfaces:
  *
  *  Theory:
  *	<<please update with a overview of the operation of this file>>
  *
  * END_DESC
 */


 #include "float.h"
 #include "dbl_float.h"

 /*
  * Double_subtract: subtract two double precision values.
  */
 int
 dbl_fsub(
 	    dbl_floating_point *leftptr,
 	    dbl_floating_point *rightptr,
 	    dbl_floating_point *dstptr,
 	    unsigned int *status)
     {
     register unsigned int signless_upper_left, signless_upper_right, save;
     register unsigned int leftp1, leftp2, rightp1, rightp2, extent;
     register unsigned int resultp1 = 0, resultp2 = 0;

     register int result_exponent, right_exponent, diff_exponent;
     register int sign_save, jumpsize;
     register boolean inexact = FALSE, underflowtrap;

     /* Create local copies of the numbers */
     Dbl_copyfromptr(leftptr,leftp1,leftp2);
     Dbl_copyfromptr(rightptr,rightp1,rightp2);

     /* A zero "save" helps discover equal operands (for later),  *
      * and is used in swapping operands (if needed).             */
     Dbl_xortointp1(leftp1,rightp1,/*to*/save);

     /*
      * check first operand for NaN's or infinity
      */
     if ((result_exponent = Dbl_exponent(leftp1)) == DBL_INFINITY_EXPONENT)
 	{
 	if (Dbl_iszero_mantissa(leftp1,leftp2))
 	    {
 	    if (Dbl_isnotnan(rightp1,rightp2))
 		{
 		if (Dbl_isinfinity(rightp1,rightp2) && save==0)
 		    {
 		    /*
 		     * invalid since operands are same signed infinity's
 		     */
 		    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                     Set_invalidflag();
                     Dbl_makequietnan(resultp1,resultp2);
 		    Dbl_copytoptr(resultp1,resultp2,dstptr);
 		    return(NOEXCEPTION);
 		    }
 		/*
 	 	 * return infinity
 	 	 */
 		Dbl_copytoptr(leftp1,leftp2,dstptr);
 		return(NOEXCEPTION);
 		}
 	    }
 	else
 	    {
             /*
              * is NaN; signaling or quiet?
              */
             if (Dbl_isone_signaling(leftp1))
 		{
                	/* trap if INVALIDTRAP enabled */
 		if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
         	/* make NaN quiet */
         	Set_invalidflag();
         	Dbl_set_quiet(leftp1);
         	}
 	    /*
 	     * is second operand a signaling NaN?
 	     */
 	    else if (Dbl_is_signalingnan(rightp1))
 		{
         	/* trap if INVALIDTRAP enabled */
                	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
 		/* make NaN quiet */
 		Set_invalidflag();
 		Dbl_set_quiet(rightp1);
 		Dbl_copytoptr(rightp1,rightp2,dstptr);
 		return(NOEXCEPTION);
 		}
 	    /*
  	     * return quiet NaN
  	     */
 	    Dbl_copytoptr(leftp1,leftp2,dstptr);
  	    return(NOEXCEPTION);
 	    }
 	} /* End left NaN or Infinity processing */
     /*
      * check second operand for NaN's or infinity
      */
     if (Dbl_isinfinity_exponent(rightp1))
 	{
 	if (Dbl_iszero_mantissa(rightp1,rightp2))
 	    {
 	    /* return infinity */
 	    Dbl_invert_sign(rightp1);
 	    Dbl_copytoptr(rightp1,rightp2,dstptr);
 	    return(NOEXCEPTION);
 	    }
         /*
          * is NaN; signaling or quiet?
          */
         if (Dbl_isone_signaling(rightp1))
 	    {
             /* trap if INVALIDTRAP enabled */
 	    if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
 	    /* make NaN quiet */
 	    Set_invalidflag();
 	    Dbl_set_quiet(rightp1);
 	    }
 	/*
 	 * return quiet NaN
  	 */
 	Dbl_copytoptr(rightp1,rightp2,dstptr);
 	return(NOEXCEPTION);
     	} /* End right NaN or Infinity processing */

     /* Invariant: Must be dealing with finite numbers */

     /* Compare operands by removing the sign */
     Dbl_copytoint_exponentmantissap1(leftp1,signless_upper_left);
     Dbl_copytoint_exponentmantissap1(rightp1,signless_upper_right);

     /* sign difference selects add or sub operation. */
     if(Dbl_ismagnitudeless(leftp2,rightp2,signless_upper_left,signless_upper_right))
 	{
 	/* Set the left operand to the larger one by XOR swap *
 	 *  First finish the first word using "save"          */
 	Dbl_xorfromintp1(save,rightp1,/*to*/rightp1);
 	Dbl_xorfromintp1(save,leftp1,/*to*/leftp1);
      	Dbl_swap_lower(leftp2,rightp2);
 	result_exponent = Dbl_exponent(leftp1);
 	Dbl_invert_sign(leftp1);
 	}
     /* Invariant:  left is not smaller than right. */

     if((right_exponent = Dbl_exponent(rightp1)) == 0)
         {
 	/* Denormalized operands.  First look for zeroes */
 	if(Dbl_iszero_mantissa(rightp1,rightp2))
 	    {
 	    /* right is zero */
 	    if(Dbl_iszero_exponentmantissa(leftp1,leftp2))
 		{
 		/* Both operands are zeros */
 		Dbl_invert_sign(rightp1);
 		if(Is_rounding_mode(ROUNDMINUS))
 		    {
 		    Dbl_or_signs(leftp1,/*with*/rightp1);
 		    }
 		else
 		    {
 		    Dbl_and_signs(leftp1,/*with*/rightp1);
 		    }
 		}
 	    else
 		{
 		/* Left is not a zero and must be the result.  Trapped
 		 * underflows are signaled if left is denormalized.  Result
 		 * is always exact. */
 		if( (result_exponent == 0) && Is_underflowtrap_enabled() )
 		    {
 		    /* need to normalize results mantissa */
 	    	    sign_save = Dbl_signextendedsign(leftp1);
 		    Dbl_leftshiftby1(leftp1,leftp2);
 		    Dbl_normalize(leftp1,leftp2,result_exponent);
 		    Dbl_set_sign(leftp1,/*using*/sign_save);
                     Dbl_setwrapped_exponent(leftp1,result_exponent,unfl);
 		    Dbl_copytoptr(leftp1,leftp2,dstptr);
 		    /* inexact = FALSE */
 		    return(UNDERFLOWEXCEPTION);
 		    }
 		}
 	    Dbl_copytoptr(leftp1,leftp2,dstptr);
 	    return(NOEXCEPTION);
 	    }

 	/* Neither are zeroes */
 	Dbl_clear_sign(rightp1);	/* Exponent is already cleared */
 	if(result_exponent == 0 )
 	    {
 	    /* Both operands are denormalized.  The result must be exact
 	     * and is simply calculated.  A sum could become normalized and a
 	     * difference could cancel to a true zero. */
 	    if( (/*signed*/int) save >= 0 )
 		{
 		Dbl_subtract(leftp1,leftp2,/*minus*/rightp1,rightp2,
 		 /*into*/resultp1,resultp2);
 		if(Dbl_iszero_mantissa(resultp1,resultp2))
 		    {
 		    if(Is_rounding_mode(ROUNDMINUS))
 			{
 			Dbl_setone_sign(resultp1);
 			}
 		    else
 			{
 			Dbl_setzero_sign(resultp1);
 			}
 		    Dbl_copytoptr(resultp1,resultp2,dstptr);
 		    return(NOEXCEPTION);
 		    }
 		}
 	    else
 		{
 		Dbl_addition(leftp1,leftp2,rightp1,rightp2,
 		 /*into*/resultp1,resultp2);
 		if(Dbl_isone_hidden(resultp1))
 		    {
 		    Dbl_copytoptr(resultp1,resultp2,dstptr);
 		    return(NOEXCEPTION);
 		    }
 		}
 	    if(Is_underflowtrap_enabled())
 		{
 		/* need to normalize result */
 	    	sign_save = Dbl_signextendedsign(resultp1);
 		Dbl_leftshiftby1(resultp1,resultp2);
 		Dbl_normalize(resultp1,resultp2,result_exponent);
 		Dbl_set_sign(resultp1,/*using*/sign_save);
                 Dbl_setwrapped_exponent(resultp1,result_exponent,unfl);
 		Dbl_copytoptr(resultp1,resultp2,dstptr);
 		/* inexact = FALSE */
 		return(UNDERFLOWEXCEPTION);
 		}
 	    Dbl_copytoptr(resultp1,resultp2,dstptr);
 	    return(NOEXCEPTION);
 	    }
 	right_exponent = 1;	/* Set exponent to reflect different bias
 				 * with denomalized numbers. */
 	}
     else
 	{
 	Dbl_clear_signexponent_set_hidden(rightp1);
 	}
     Dbl_clear_exponent_set_hidden(leftp1);
     diff_exponent = result_exponent - right_exponent;

     /*
      * Special case alignment of operands that would force alignment
      * beyond the extent of the extension.  A further optimization
      * could special case this but only reduces the path length for this
      * infrequent case.
      */
     if(diff_exponent > DBL_THRESHOLD)
 	{
 	diff_exponent = DBL_THRESHOLD;
 	}

     /* Align right operand by shifting to right */
     Dbl_right_align(/*operand*/rightp1,rightp2,/*shifted by*/diff_exponent,
      /*and lower to*/extent);

     /* Treat sum and difference of the operands separately. */
     if( (/*signed*/int) save >= 0 )
 	{
 	/*
 	 * Difference of the two operands.  Their can be no overflow.  A
 	 * borrow can occur out of the hidden bit and force a post
 	 * normalization phase.
 	 */
 	Dbl_subtract_withextension(leftp1,leftp2,/*minus*/rightp1,rightp2,
 	 /*with*/extent,/*into*/resultp1,resultp2);
 	if(Dbl_iszero_hidden(resultp1))
 	    {
 	    /* Handle normalization */
 	    /* A straight forward algorithm would now shift the result
 	     * and extension left until the hidden bit becomes one.  Not
 	     * all of the extension bits need participate in the shift.
 	     * Only the two most significant bits (round and guard) are
 	     * needed.  If only a single shift is needed then the guard
 	     * bit becomes a significant low order bit and the extension
 	     * must participate in the rounding.  If more than a single
 	     * shift is needed, then all bits to the right of the guard
 	     * bit are zeros, and the guard bit may or may not be zero. */
 	    sign_save = Dbl_signextendedsign(resultp1);
             Dbl_leftshiftby1_withextent(resultp1,resultp2,extent,resultp1,resultp2);

             /* Need to check for a zero result.  The sign and exponent
 	     * fields have already been zeroed.  The more efficient test
 	     * of the full object can be used.
 	     */
     	    if(Dbl_iszero(resultp1,resultp2))
 		/* Must have been "x-x" or "x+(-x)". */
 		{
 		if(Is_rounding_mode(ROUNDMINUS)) Dbl_setone_sign(resultp1);
 		Dbl_copytoptr(resultp1,resultp2,dstptr);
 		return(NOEXCEPTION);
 		}
 	    result_exponent--;
 	    /* Look to see if normalization is finished. */
 	    if(Dbl_isone_hidden(resultp1))
 		{
 		if(result_exponent==0)
 		    {
 		    /* Denormalized, exponent should be zero.  Left operand *
 		     * was normalized, so extent (guard, round) was zero    */
 		    goto underflow;
 		    }
 		else
 		    {
 		    /* No further normalization is needed. */
 		    Dbl_set_sign(resultp1,/*using*/sign_save);
 	    	    Ext_leftshiftby1(extent);
 		    goto round;
 		    }
 		}

 	    /* Check for denormalized, exponent should be zero.  Left    *
 	     * operand was normalized, so extent (guard, round) was zero */
 	    if(!(underflowtrap = Is_underflowtrap_enabled()) &&
 	       result_exponent==0) goto underflow;

 	    /* Shift extension to complete one bit of normalization and
 	     * update exponent. */
 	    Ext_leftshiftby1(extent);

 	    /* Discover first one bit to determine shift amount.  Use a
 	     * modified binary search.  We have already shifted the result
 	     * one position right and still not found a one so the remainder
 	     * of the extension must be zero and simplifies rounding. */
 	    /* Scan bytes */
 	    while(Dbl_iszero_hiddenhigh7mantissa(resultp1))
 		{
 		Dbl_leftshiftby8(resultp1,resultp2);
 		if((result_exponent -= 8) <= 0  && !underflowtrap)
 		    goto underflow;
 		}
 	    /* Now narrow it down to the nibble */
 	    if(Dbl_iszero_hiddenhigh3mantissa(resultp1))
 		{
 		/* The lower nibble contains the normalizing one */
 		Dbl_leftshiftby4(resultp1,resultp2);
 		if((result_exponent -= 4) <= 0 && !underflowtrap)
 		    goto underflow;
 		}
 	    /* Select case were first bit is set (already normalized)
 	     * otherwise select the proper shift. */
 	    if((jumpsize = Dbl_hiddenhigh3mantissa(resultp1)) > 7)
 		{
 		/* Already normalized */
 		if(result_exponent <= 0) goto underflow;
 		Dbl_set_sign(resultp1,/*using*/sign_save);
 		Dbl_set_exponent(resultp1,/*using*/result_exponent);
 		Dbl_copytoptr(resultp1,resultp2,dstptr);
 		return(NOEXCEPTION);
 		}
 	    Dbl_sethigh4bits(resultp1,/*using*/sign_save);
 	    switch(jumpsize)
 		{
 		case 1:
 		    {
 		    Dbl_leftshiftby3(resultp1,resultp2);
 		    result_exponent -= 3;
 		    break;
 		    }
 		case 2:
 		case 3:
 		    {
 		    Dbl_leftshiftby2(resultp1,resultp2);
 		    result_exponent -= 2;
 		    break;
 		    }
 		case 4:
 		case 5:
 		case 6:
 		case 7:
 		    {
 		    Dbl_leftshiftby1(resultp1,resultp2);
 		    result_exponent -= 1;
 		    break;
 		    }
 		}
 	    if(result_exponent > 0)
 		{
 		Dbl_set_exponent(resultp1,/*using*/result_exponent);
 		Dbl_copytoptr(resultp1,resultp2,dstptr);
 		return(NOEXCEPTION);		/* Sign bit is already set */
 		}
 	    /* Fixup potential underflows */
 	  underflow:
 	    if(Is_underflowtrap_enabled())
 		{
 		Dbl_set_sign(resultp1,sign_save);
                 Dbl_setwrapped_exponent(resultp1,result_exponent,unfl);
 		Dbl_copytoptr(resultp1,resultp2,dstptr);
 		/* inexact = FALSE */
 		return(UNDERFLOWEXCEPTION);
 		}
 	    /*
 	     * Since we cannot get an inexact denormalized result,
 	     * we can now return.
 	     */
 	    Dbl_fix_overshift(resultp1,resultp2,(1-result_exponent),extent);
 	    Dbl_clear_signexponent(resultp1);
 	    Dbl_set_sign(resultp1,sign_save);
 	    Dbl_copytoptr(resultp1,resultp2,dstptr);
 	    return(NOEXCEPTION);
 	    } /* end if(hidden...)... */
 	/* Fall through and round */
 	} /* end if(save >= 0)... */
     else
 	{
 	/* Subtract magnitudes */
 	Dbl_addition(leftp1,leftp2,rightp1,rightp2,/*to*/resultp1,resultp2);
 	if(Dbl_isone_hiddenoverflow(resultp1))
 	    {
 	    /* Prenormalization required. */
 	    Dbl_rightshiftby1_withextent(resultp2,extent,extent);
 	    Dbl_arithrightshiftby1(resultp1,resultp2);
 	    result_exponent++;
 	    } /* end if hiddenoverflow... */
 	} /* end else ...subtract magnitudes... */

     /* Round the result.  If the extension is all zeros,then the result is
      * exact.  Otherwise round in the correct direction.  No underflow is
      * possible. If a postnormalization is necessary, then the mantissa is
      * all zeros so no shift is needed. */
   round:
     if(Ext_isnotzero(extent))
 	{
 	inexact = TRUE;
 	switch(Rounding_mode())
 	    {
 	    case ROUNDNEAREST: /* The default. */
 	    if(Ext_isone_sign(extent))
 		{
 		/* at least 1/2 ulp */
 		if(Ext_isnotzero_lower(extent)  ||
 		  Dbl_isone_lowmantissap2(resultp2))
 		    {
 		    /* either exactly half way and odd or more than 1/2ulp */
 		    Dbl_increment(resultp1,resultp2);
 		    }
 		}
 	    break;

 	    case ROUNDPLUS:
 	    if(Dbl_iszero_sign(resultp1))
 		{
 		/* Round up positive results */
 		Dbl_increment(resultp1,resultp2);
 		}
 	    break;

 	    case ROUNDMINUS:
 	    if(Dbl_isone_sign(resultp1))
 		{
 		/* Round down negative results */
 		Dbl_increment(resultp1,resultp2);
 		}

 	    case ROUNDZERO:;
 	    /* truncate is simple */
 	    } /* end switch... */
 	if(Dbl_isone_hiddenoverflow(resultp1)) result_exponent++;
 	}
     if(result_exponent == DBL_INFINITY_EXPONENT)
         {
         /* Overflow */
         if(Is_overflowtrap_enabled())
 	    {
 	    Dbl_setwrapped_exponent(resultp1,result_exponent,ovfl);
 	    Dbl_copytoptr(resultp1,resultp2,dstptr);
 	    if (inexact)
 	    if (Is_inexacttrap_enabled())
 		return(OVERFLOWEXCEPTION | INEXACTEXCEPTION);
 		else Set_inexactflag();
 	    return(OVERFLOWEXCEPTION);
 	    }
         else
 	    {
 	    inexact = TRUE;
 	    Set_overflowflag();
 	    Dbl_setoverflow(resultp1,resultp2);
 	    }
 	}
     else Dbl_set_exponent(resultp1,result_exponent);
     Dbl_copytoptr(resultp1,resultp2,dstptr);
     if(inexact)
 	if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
 	else Set_inexactflag();
     return(NOEXCEPTION);
     }
	// SPDX-License-Identifier: GPL-2.0-or-later
	/*
	* Linux/PA-RISC Project (http://www.parisc-linux.org/)
	*
	* Floating-point emulation code
	* Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
	*/
	/*
	* BEGIN_DESC
	*
	* File:
	* @(#) pa/spmath/dfsub.c $Revision: 1.1 $
	*
	* Purpose:
	* Double_subtract: subtract two double precision values.
	*
	* External Interfaces:
	* dbl_fsub(leftptr, rightptr, dstptr, status)
	*
	* Internal Interfaces:
	*
	* Theory:
	* <<please update with a overview of the operation of this file>>
	*
	* END_DESC
	*/


	#include "float.h"
	#include "dbl_float.h"

	/*
	* Double_subtract: subtract two double precision values.
	*/
	int
	dbl_fsub(
	dbl_floating_point *leftptr,
	dbl_floating_point *rightptr,
	dbl_floating_point *dstptr,
	unsigned int *status)
	{
	register unsigned int signless_upper_left, signless_upper_right, save;
	register unsigned int leftp1, leftp2, rightp1, rightp2, extent;
	register unsigned int resultp1 = 0, resultp2 = 0;

	register int result_exponent, right_exponent, diff_exponent;
	register int sign_save, jumpsize;
	register boolean inexact = FALSE, underflowtrap;

	/* Create local copies of the numbers */
	Dbl_copyfromptr(leftptr,leftp1,leftp2);
	Dbl_copyfromptr(rightptr,rightp1,rightp2);

	/* A zero "save" helps discover equal operands (for later), *
	* and is used in swapping operands (if needed). */
	Dbl_xortointp1(leftp1,rightp1,/to/save);

	/*
	* check first operand for NaN's or infinity
	*/
	if ((result_exponent = Dbl_exponent(leftp1)) == DBL_INFINITY_EXPONENT)
	{
	if (Dbl_iszero_mantissa(leftp1,leftp2))
	{
	if (Dbl_isnotnan(rightp1,rightp2))
	{
	if (Dbl_isinfinity(rightp1,rightp2) && save==0)
	{
	/*
	* invalid since operands are same signed infinity's
	*/
	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
	Set_invalidflag();
	Dbl_makequietnan(resultp1,resultp2);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	/*
	* return infinity
	*/
	Dbl_copytoptr(leftp1,leftp2,dstptr);
	return(NOEXCEPTION);
	}
	}
	else
	{
	/*
	* is NaN; signaling or quiet?
	*/
	if (Dbl_isone_signaling(leftp1))
	{
	/* trap if INVALIDTRAP enabled */
	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
	/* make NaN quiet */
	Set_invalidflag();
	Dbl_set_quiet(leftp1);
	}
	/*
	* is second operand a signaling NaN?
	*/
	else if (Dbl_is_signalingnan(rightp1))
	{
	/* trap if INVALIDTRAP enabled */
	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
	/* make NaN quiet */
	Set_invalidflag();
	Dbl_set_quiet(rightp1);
	Dbl_copytoptr(rightp1,rightp2,dstptr);
	return(NOEXCEPTION);
	}
	/*
	* return quiet NaN
	*/
	Dbl_copytoptr(leftp1,leftp2,dstptr);
	return(NOEXCEPTION);
	}
	} /* End left NaN or Infinity processing */
	/*
	* check second operand for NaN's or infinity
	*/
	if (Dbl_isinfinity_exponent(rightp1))
	{
	if (Dbl_iszero_mantissa(rightp1,rightp2))
	{
	/* return infinity */
	Dbl_invert_sign(rightp1);
	Dbl_copytoptr(rightp1,rightp2,dstptr);
	return(NOEXCEPTION);
	}
	/*
	* is NaN; signaling or quiet?
	*/
	if (Dbl_isone_signaling(rightp1))
	{
	/* trap if INVALIDTRAP enabled */
	if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
	/* make NaN quiet */
	Set_invalidflag();
	Dbl_set_quiet(rightp1);
	}
	/*
	* return quiet NaN
	*/
	Dbl_copytoptr(rightp1,rightp2,dstptr);
	return(NOEXCEPTION);
	} /* End right NaN or Infinity processing */

	/* Invariant: Must be dealing with finite numbers */

	/* Compare operands by removing the sign */
	Dbl_copytoint_exponentmantissap1(leftp1,signless_upper_left);
	Dbl_copytoint_exponentmantissap1(rightp1,signless_upper_right);

	/* sign difference selects add or sub operation. */
	if(Dbl_ismagnitudeless(leftp2,rightp2,signless_upper_left,signless_upper_right))
	{
	/* Set the left operand to the larger one by XOR swap *
	* First finish the first word using "save" */
	Dbl_xorfromintp1(save,rightp1,/to/rightp1);
	Dbl_xorfromintp1(save,leftp1,/to/leftp1);
	Dbl_swap_lower(leftp2,rightp2);
	result_exponent = Dbl_exponent(leftp1);
	Dbl_invert_sign(leftp1);
	}
	/* Invariant: left is not smaller than right. */

	if((right_exponent = Dbl_exponent(rightp1)) == 0)
	{
	/* Denormalized operands. First look for zeroes */
	if(Dbl_iszero_mantissa(rightp1,rightp2))
	{
	/* right is zero */
	if(Dbl_iszero_exponentmantissa(leftp1,leftp2))
	{
	/* Both operands are zeros */
	Dbl_invert_sign(rightp1);
	if(Is_rounding_mode(ROUNDMINUS))
	{
	Dbl_or_signs(leftp1,/with/rightp1);
	}
	else
	{
	Dbl_and_signs(leftp1,/with/rightp1);
	}
	}
	else
	{
	/* Left is not a zero and must be the result. Trapped
	* underflows are signaled if left is denormalized. Result
	* is always exact. */
	if( (result_exponent == 0) && Is_underflowtrap_enabled() )
	{
	/* need to normalize results mantissa */
	sign_save = Dbl_signextendedsign(leftp1);
	Dbl_leftshiftby1(leftp1,leftp2);
	Dbl_normalize(leftp1,leftp2,result_exponent);
	Dbl_set_sign(leftp1,/using/sign_save);
	Dbl_setwrapped_exponent(leftp1,result_exponent,unfl);
	Dbl_copytoptr(leftp1,leftp2,dstptr);
	/* inexact = FALSE */
	return(UNDERFLOWEXCEPTION);
	}
	}
	Dbl_copytoptr(leftp1,leftp2,dstptr);
	return(NOEXCEPTION);
	}

	/* Neither are zeroes */
	Dbl_clear_sign(rightp1); /* Exponent is already cleared */
	if(result_exponent == 0 )
	{
	/* Both operands are denormalized. The result must be exact
	* and is simply calculated. A sum could become normalized and a
	* difference could cancel to a true zero. */
	if( (/signed/int) save >= 0 )
	{
	Dbl_subtract(leftp1,leftp2,/minus/rightp1,rightp2,
	/into/resultp1,resultp2);
	if(Dbl_iszero_mantissa(resultp1,resultp2))
	{
	if(Is_rounding_mode(ROUNDMINUS))
	{
	Dbl_setone_sign(resultp1);
	}
	else
	{
	Dbl_setzero_sign(resultp1);
	}
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	}
	else
	{
	Dbl_addition(leftp1,leftp2,rightp1,rightp2,
	/into/resultp1,resultp2);
	if(Dbl_isone_hidden(resultp1))
	{
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	}
	if(Is_underflowtrap_enabled())
	{
	/* need to normalize result */
	sign_save = Dbl_signextendedsign(resultp1);
	Dbl_leftshiftby1(resultp1,resultp2);
	Dbl_normalize(resultp1,resultp2,result_exponent);
	Dbl_set_sign(resultp1,/using/sign_save);
	Dbl_setwrapped_exponent(resultp1,result_exponent,unfl);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	/* inexact = FALSE */
	return(UNDERFLOWEXCEPTION);
	}
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	right_exponent = 1; /* Set exponent to reflect different bias
	* with denomalized numbers. */
	}
	else
	{
	Dbl_clear_signexponent_set_hidden(rightp1);
	}
	Dbl_clear_exponent_set_hidden(leftp1);
	diff_exponent = result_exponent - right_exponent;

	/*
	* Special case alignment of operands that would force alignment
	* beyond the extent of the extension. A further optimization
	* could special case this but only reduces the path length for this
	* infrequent case.
	*/
	if(diff_exponent > DBL_THRESHOLD)
	{
	diff_exponent = DBL_THRESHOLD;
	}

	/* Align right operand by shifting to right */
	Dbl_right_align(/operand/rightp1,rightp2,/shifted by/diff_exponent,
	/and lower to/extent);

	/* Treat sum and difference of the operands separately. */
	if( (/signed/int) save >= 0 )
	{
	/*
	* Difference of the two operands. Their can be no overflow. A
	* borrow can occur out of the hidden bit and force a post
	* normalization phase.
	*/
	Dbl_subtract_withextension(leftp1,leftp2,/minus/rightp1,rightp2,
	/with/extent,/into/resultp1,resultp2);
	if(Dbl_iszero_hidden(resultp1))
	{
	/* Handle normalization */
	/* A straight forward algorithm would now shift the result
	* and extension left until the hidden bit becomes one. Not
	* all of the extension bits need participate in the shift.
	* Only the two most significant bits (round and guard) are
	* needed. If only a single shift is needed then the guard
	* bit becomes a significant low order bit and the extension
	* must participate in the rounding. If more than a single
	* shift is needed, then all bits to the right of the guard
	* bit are zeros, and the guard bit may or may not be zero. */
	sign_save = Dbl_signextendedsign(resultp1);
	Dbl_leftshiftby1_withextent(resultp1,resultp2,extent,resultp1,resultp2);

	/* Need to check for a zero result. The sign and exponent
	* fields have already been zeroed. The more efficient test
	* of the full object can be used.
	*/
	if(Dbl_iszero(resultp1,resultp2))
	/* Must have been "x-x" or "x+(-x)". */
	{
	if(Is_rounding_mode(ROUNDMINUS)) Dbl_setone_sign(resultp1);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	result_exponent--;
	/* Look to see if normalization is finished. */
	if(Dbl_isone_hidden(resultp1))
	{
	if(result_exponent==0)
	{
	/* Denormalized, exponent should be zero. Left operand *
	* was normalized, so extent (guard, round) was zero */
	goto underflow;
	}
	else
	{
	/* No further normalization is needed. */
	Dbl_set_sign(resultp1,/using/sign_save);
	Ext_leftshiftby1(extent);
	goto round;
	}
	}

	/* Check for denormalized, exponent should be zero. Left *
	* operand was normalized, so extent (guard, round) was zero */
	if(!(underflowtrap = Is_underflowtrap_enabled()) &&
	result_exponent==0) goto underflow;

	/* Shift extension to complete one bit of normalization and
	* update exponent. */
	Ext_leftshiftby1(extent);

	/* Discover first one bit to determine shift amount. Use a
	* modified binary search. We have already shifted the result
	* one position right and still not found a one so the remainder
	* of the extension must be zero and simplifies rounding. */
	/* Scan bytes */
	while(Dbl_iszero_hiddenhigh7mantissa(resultp1))
	{
	Dbl_leftshiftby8(resultp1,resultp2);
	if((result_exponent -= 8) <= 0 && !underflowtrap)
	goto underflow;
	}
	/* Now narrow it down to the nibble */
	if(Dbl_iszero_hiddenhigh3mantissa(resultp1))
	{
	/* The lower nibble contains the normalizing one */
	Dbl_leftshiftby4(resultp1,resultp2);
	if((result_exponent -= 4) <= 0 && !underflowtrap)
	goto underflow;
	}
	/* Select case were first bit is set (already normalized)
	* otherwise select the proper shift. */
	if((jumpsize = Dbl_hiddenhigh3mantissa(resultp1)) > 7)
	{
	/* Already normalized */
	if(result_exponent <= 0) goto underflow;
	Dbl_set_sign(resultp1,/using/sign_save);
	Dbl_set_exponent(resultp1,/using/result_exponent);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	}
	Dbl_sethigh4bits(resultp1,/using/sign_save);
	switch(jumpsize)
	{
	case 1:
	{
	Dbl_leftshiftby3(resultp1,resultp2);
	result_exponent -= 3;
	break;
	}
	case 2:
	case 3:
	{
	Dbl_leftshiftby2(resultp1,resultp2);
	result_exponent -= 2;
	break;
	}
	case 4:
	case 5:
	case 6:
	case 7:
	{
	Dbl_leftshiftby1(resultp1,resultp2);
	result_exponent -= 1;
	break;
	}
	}
	if(result_exponent > 0)
	{
	Dbl_set_exponent(resultp1,/using/result_exponent);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION); /* Sign bit is already set */
	}
	/* Fixup potential underflows */
	underflow:
	if(Is_underflowtrap_enabled())
	{
	Dbl_set_sign(resultp1,sign_save);
	Dbl_setwrapped_exponent(resultp1,result_exponent,unfl);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	/* inexact = FALSE */
	return(UNDERFLOWEXCEPTION);
	}
	/*
	* Since we cannot get an inexact denormalized result,
	* we can now return.
	*/
	Dbl_fix_overshift(resultp1,resultp2,(1-result_exponent),extent);
	Dbl_clear_signexponent(resultp1);
	Dbl_set_sign(resultp1,sign_save);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	return(NOEXCEPTION);
	} /* end if(hidden...)... */
	/* Fall through and round */
	} /* end if(save >= 0)... */
	else
	{
	/* Subtract magnitudes */
	Dbl_addition(leftp1,leftp2,rightp1,rightp2,/to/resultp1,resultp2);
	if(Dbl_isone_hiddenoverflow(resultp1))
	{
	/* Prenormalization required. */
	Dbl_rightshiftby1_withextent(resultp2,extent,extent);
	Dbl_arithrightshiftby1(resultp1,resultp2);
	result_exponent++;
	} /* end if hiddenoverflow... */
	} /* end else ...subtract magnitudes... */

	/* Round the result. If the extension is all zeros,then the result is
	* exact. Otherwise round in the correct direction. No underflow is
	* possible. If a postnormalization is necessary, then the mantissa is
	* all zeros so no shift is needed. */
	round:
	if(Ext_isnotzero(extent))
	{
	inexact = TRUE;
	switch(Rounding_mode())
	{
	case ROUNDNEAREST: /* The default. */
	if(Ext_isone_sign(extent))
	{
	/* at least 1/2 ulp */
	if(Ext_isnotzero_lower(extent) \|\|
	Dbl_isone_lowmantissap2(resultp2))
	{
	/* either exactly half way and odd or more than 1/2ulp */
	Dbl_increment(resultp1,resultp2);
	}
	}
	break;

	case ROUNDPLUS:
	if(Dbl_iszero_sign(resultp1))
	{
	/* Round up positive results */
	Dbl_increment(resultp1,resultp2);
	}
	break;

	case ROUNDMINUS:
	if(Dbl_isone_sign(resultp1))
	{
	/* Round down negative results */
	Dbl_increment(resultp1,resultp2);
	}

	case ROUNDZERO:;
	/* truncate is simple */
	} /* end switch... */
	if(Dbl_isone_hiddenoverflow(resultp1)) result_exponent++;
	}
	if(result_exponent == DBL_INFINITY_EXPONENT)
	{
	/* Overflow */
	if(Is_overflowtrap_enabled())
	{
	Dbl_setwrapped_exponent(resultp1,result_exponent,ovfl);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	if (inexact)
	if (Is_inexacttrap_enabled())
	return(OVERFLOWEXCEPTION \| INEXACTEXCEPTION);
	else Set_inexactflag();
	return(OVERFLOWEXCEPTION);
	}
	else
	{
	inexact = TRUE;
	Set_overflowflag();
	Dbl_setoverflow(resultp1,resultp2);
	}
	}
	else Dbl_set_exponent(resultp1,result_exponent);
	Dbl_copytoptr(resultp1,resultp2,dstptr);
	if(inexact)
	if(Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
	else Set_inexactflag();
	return(NOEXCEPTION);
	}