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dfdiv.c

/*
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 *
 * Floating-point emulation code
 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
 *
 *    This program is free software; you can redistribute it and/or modify
 *    it under the terms of the GNU General Public License as published by
 *    the Free Software Foundation; either version 2, or (at your option)
 *    any later version.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU General Public License for more details.
 *
 *    You should have received a copy of the GNU General Public License
 *    along with this program; if not, write to the Free Software
 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
/*
 * BEGIN_DESC
 *
 *  File:
 *    @(#)  pa/spmath/dfdiv.c       $Revision: 1.1 $
 *
 *  Purpose:
 *    Double Precision Floating-point Divide
 *
 *  External Interfaces:
 *    dbl_fdiv(srcptr1,srcptr2,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 Precision Floating-point Divide
 */

int
dbl_fdiv (dbl_floating_point * srcptr1, dbl_floating_point * srcptr2,
        dbl_floating_point * dstptr, unsigned int *status)
{
      register unsigned int opnd1p1, opnd1p2, opnd2p1, opnd2p2;
      register unsigned int opnd3p1, opnd3p2, resultp1, resultp2;
      register int dest_exponent, count;
      register boolean inexact = FALSE, guardbit = FALSE, stickybit = FALSE;
      boolean is_tiny;

      Dbl_copyfromptr(srcptr1,opnd1p1,opnd1p2);
      Dbl_copyfromptr(srcptr2,opnd2p1,opnd2p2);
      /* 
       * set sign bit of result 
       */
      if (Dbl_sign(opnd1p1) ^ Dbl_sign(opnd2p1)) 
            Dbl_setnegativezerop1(resultp1);  
      else Dbl_setzerop1(resultp1);
      /*
       * check first operand for NaN's or infinity
       */
      if (Dbl_isinfinity_exponent(opnd1p1)) {
            if (Dbl_iszero_mantissa(opnd1p1,opnd1p2)) {
                  if (Dbl_isnotnan(opnd2p1,opnd2p2)) {
                        if (Dbl_isinfinity(opnd2p1,opnd2p2)) {
                              /* 
                               * invalid since both operands 
                               * are infinity 
                               */
                              if (Is_invalidtrap_enabled())
                                          return(INVALIDEXCEPTION);
                                    Set_invalidflag();
                                    Dbl_makequietnan(resultp1,resultp2);
                              Dbl_copytoptr(resultp1,resultp2,dstptr);
                              return(NOEXCEPTION);
                        }
                        /*
                         * return infinity
                         */
                        Dbl_setinfinity_exponentmantissa(resultp1,resultp2);
                        Dbl_copytoptr(resultp1,resultp2,dstptr);
                        return(NOEXCEPTION);
                  }
            }
            else {
                  /*
                   * is NaN; signaling or quiet?
                   */
                  if (Dbl_isone_signaling(opnd1p1)) {
                              /* trap if INVALIDTRAP enabled */
                              if (Is_invalidtrap_enabled())
                                    return(INVALIDEXCEPTION);
                              /* make NaN quiet */
                              Set_invalidflag();
                              Dbl_set_quiet(opnd1p1);
                  }
                  /* 
                   * is second operand a signaling NaN? 
                   */
                  else if (Dbl_is_signalingnan(opnd2p1)) {
                              /* trap if INVALIDTRAP enabled */
                              if (Is_invalidtrap_enabled())
                                    return(INVALIDEXCEPTION);
                              /* make NaN quiet */
                              Set_invalidflag();
                              Dbl_set_quiet(opnd2p1);
                        Dbl_copytoptr(opnd2p1,opnd2p2,dstptr);
                        return(NOEXCEPTION);
                  }
                  /*
                   * return quiet NaN
                   */
                  Dbl_copytoptr(opnd1p1,opnd1p2,dstptr);
                  return(NOEXCEPTION);
            }
      }
      /*
       * check second operand for NaN's or infinity
       */
      if (Dbl_isinfinity_exponent(opnd2p1)) {
            if (Dbl_iszero_mantissa(opnd2p1,opnd2p2)) {
                  /*
                   * return zero
                   */
                  Dbl_setzero_exponentmantissa(resultp1,resultp2);
                  Dbl_copytoptr(resultp1,resultp2,dstptr);
                  return(NOEXCEPTION);
            }
                /*
                 * is NaN; signaling or quiet?
                 */
                if (Dbl_isone_signaling(opnd2p1)) {
                        /* trap if INVALIDTRAP enabled */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        /* make NaN quiet */
                        Set_invalidflag();
                        Dbl_set_quiet(opnd2p1);
                }
                /*
                 * return quiet NaN
                 */
            Dbl_copytoptr(opnd2p1,opnd2p2,dstptr);
                return(NOEXCEPTION);
      }
        /*
         * check for division by zero
         */
        if (Dbl_iszero_exponentmantissa(opnd2p1,opnd2p2)) {
                if (Dbl_iszero_exponentmantissa(opnd1p1,opnd1p2)) {
                        /* invalid since both operands are zero */
                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
                        Set_invalidflag();
                        Dbl_makequietnan(resultp1,resultp2);
                        Dbl_copytoptr(resultp1,resultp2,dstptr);
                        return(NOEXCEPTION);
                }
                if (Is_divisionbyzerotrap_enabled())
                        return(DIVISIONBYZEROEXCEPTION);
                Set_divisionbyzeroflag();
                Dbl_setinfinity_exponentmantissa(resultp1,resultp2);
                Dbl_copytoptr(resultp1,resultp2,dstptr);
                return(NOEXCEPTION);
        }
      /*
       * Generate exponent 
       */
      dest_exponent = Dbl_exponent(opnd1p1) - Dbl_exponent(opnd2p1) + DBL_BIAS;

      /*
       * Generate mantissa
       */
      if (Dbl_isnotzero_exponent(opnd1p1)) {
            /* set hidden bit */
            Dbl_clear_signexponent_set_hidden(opnd1p1);
      }
      else {
            /* check for zero */
            if (Dbl_iszero_mantissa(opnd1p1,opnd1p2)) {
                  Dbl_setzero_exponentmantissa(resultp1,resultp2);
                  Dbl_copytoptr(resultp1,resultp2,dstptr);
                  return(NOEXCEPTION);
            }
                /* is denormalized, want to normalize */
                Dbl_clear_signexponent(opnd1p1);
                Dbl_leftshiftby1(opnd1p1,opnd1p2);
            Dbl_normalize(opnd1p1,opnd1p2,dest_exponent);
      }
      /* opnd2 needs to have hidden bit set with msb in hidden bit */
      if (Dbl_isnotzero_exponent(opnd2p1)) {
            Dbl_clear_signexponent_set_hidden(opnd2p1);
      }
      else {
                /* is denormalized; want to normalize */
                Dbl_clear_signexponent(opnd2p1);
                Dbl_leftshiftby1(opnd2p1,opnd2p2);
                while (Dbl_iszero_hiddenhigh7mantissa(opnd2p1)) {
                        dest_exponent+=8;
                        Dbl_leftshiftby8(opnd2p1,opnd2p2);
                }
                if (Dbl_iszero_hiddenhigh3mantissa(opnd2p1)) {
                        dest_exponent+=4;
                        Dbl_leftshiftby4(opnd2p1,opnd2p2);
                }
                while (Dbl_iszero_hidden(opnd2p1)) {
                        dest_exponent++;
                        Dbl_leftshiftby1(opnd2p1,opnd2p2);
                }
      }

      /* Divide the source mantissas */

      /* 
       * A non-restoring divide algorithm is used.
       */
      Twoword_subtract(opnd1p1,opnd1p2,opnd2p1,opnd2p2);
      Dbl_setzero(opnd3p1,opnd3p2);
      for (count=1; count <= DBL_P && (opnd1p1 || opnd1p2); count++) {
            Dbl_leftshiftby1(opnd1p1,opnd1p2);
            Dbl_leftshiftby1(opnd3p1,opnd3p2);
            if (Dbl_iszero_sign(opnd1p1)) {
                  Dbl_setone_lowmantissap2(opnd3p2);
                  Twoword_subtract(opnd1p1,opnd1p2,opnd2p1,opnd2p2);
            }
            else {
                  Twoword_add(opnd1p1, opnd1p2, opnd2p1, opnd2p2);
            }
      }
      if (count <= DBL_P) {
            Dbl_leftshiftby1(opnd3p1,opnd3p2);
            Dbl_setone_lowmantissap2(opnd3p2);
            Dbl_leftshift(opnd3p1,opnd3p2,(DBL_P-count));
            if (Dbl_iszero_hidden(opnd3p1)) {
                  Dbl_leftshiftby1(opnd3p1,opnd3p2);
                  dest_exponent--;
            }
      }
      else {
            if (Dbl_iszero_hidden(opnd3p1)) {
                  /* need to get one more bit of result */
                  Dbl_leftshiftby1(opnd1p1,opnd1p2);
                  Dbl_leftshiftby1(opnd3p1,opnd3p2);
                  if (Dbl_iszero_sign(opnd1p1)) {
                        Dbl_setone_lowmantissap2(opnd3p2);
                        Twoword_subtract(opnd1p1,opnd1p2,opnd2p1,opnd2p2);
                  }
                  else {
                        Twoword_add(opnd1p1,opnd1p2,opnd2p1,opnd2p2);
                  }
                  dest_exponent--;
            }
            if (Dbl_iszero_sign(opnd1p1)) guardbit = TRUE;
            stickybit = Dbl_allp1(opnd1p1) || Dbl_allp2(opnd1p2);
      }
      inexact = guardbit | stickybit;

      /* 
       * round result 
       */
      if (inexact && (dest_exponent > 0 || Is_underflowtrap_enabled())) {
            Dbl_clear_signexponent(opnd3p1);
            switch (Rounding_mode()) {
                  case ROUNDPLUS: 
                        if (Dbl_iszero_sign(resultp1)) 
                              Dbl_increment(opnd3p1,opnd3p2);
                        break;
                  case ROUNDMINUS: 
                        if (Dbl_isone_sign(resultp1)) 
                              Dbl_increment(opnd3p1,opnd3p2);
                        break;
                  case ROUNDNEAREST:
                        if (guardbit && (stickybit || 
                            Dbl_isone_lowmantissap2(opnd3p2))) {
                                    Dbl_increment(opnd3p1,opnd3p2);
                        }
            }
            if (Dbl_isone_hidden(opnd3p1)) dest_exponent++;
      }
      Dbl_set_mantissa(resultp1,resultp2,opnd3p1,opnd3p2);

        /* 
         * Test for overflow
         */
      if (dest_exponent >= DBL_INFINITY_EXPONENT) {
                /* trap if OVERFLOWTRAP enabled */
                if (Is_overflowtrap_enabled()) {
                        /*
                         * Adjust bias of result
                         */
                        Dbl_setwrapped_exponent(resultp1,dest_exponent,ovfl);
                        Dbl_copytoptr(resultp1,resultp2,dstptr);
                        if (inexact) 
                            if (Is_inexacttrap_enabled())
                                return(OVERFLOWEXCEPTION | INEXACTEXCEPTION);
                            else Set_inexactflag();
                        return(OVERFLOWEXCEPTION);
                }
            Set_overflowflag();
                /* set result to infinity or largest number */
            Dbl_setoverflow(resultp1,resultp2);
            inexact = TRUE;
      }
        /* 
         * Test for underflow
         */
      else if (dest_exponent <= 0) {
                /* trap if UNDERFLOWTRAP enabled */
                if (Is_underflowtrap_enabled()) {
                        /*
                         * Adjust bias of result
                         */
                        Dbl_setwrapped_exponent(resultp1,dest_exponent,unfl);
                        Dbl_copytoptr(resultp1,resultp2,dstptr);
                        if (inexact) 
                            if (Is_inexacttrap_enabled())
                                return(UNDERFLOWEXCEPTION | INEXACTEXCEPTION);
                            else Set_inexactflag();
                        return(UNDERFLOWEXCEPTION);
                }

            /* Determine if should set underflow flag */
            is_tiny = TRUE;
            if (dest_exponent == 0 && inexact) {
                  switch (Rounding_mode()) {
                  case ROUNDPLUS: 
                        if (Dbl_iszero_sign(resultp1)) {
                              Dbl_increment(opnd3p1,opnd3p2);
                              if (Dbl_isone_hiddenoverflow(opnd3p1))
                                  is_tiny = FALSE;
                              Dbl_decrement(opnd3p1,opnd3p2);
                        }
                        break;
                  case ROUNDMINUS: 
                        if (Dbl_isone_sign(resultp1)) {
                              Dbl_increment(opnd3p1,opnd3p2);
                              if (Dbl_isone_hiddenoverflow(opnd3p1))
                                  is_tiny = FALSE;
                              Dbl_decrement(opnd3p1,opnd3p2);
                        }
                        break;
                  case ROUNDNEAREST:
                        if (guardbit && (stickybit || 
                            Dbl_isone_lowmantissap2(opnd3p2))) {
                                    Dbl_increment(opnd3p1,opnd3p2);
                              if (Dbl_isone_hiddenoverflow(opnd3p1))
                                  is_tiny = FALSE;
                              Dbl_decrement(opnd3p1,opnd3p2);
                        }
                        break;
                  }
            }

                /*
                 * denormalize result or set to signed zero
                 */
            stickybit = inexact;
            Dbl_denormalize(opnd3p1,opnd3p2,dest_exponent,guardbit,
             stickybit,inexact);

            /* return rounded number */ 
            if (inexact) {
                  switch (Rounding_mode()) {
                  case ROUNDPLUS:
                        if (Dbl_iszero_sign(resultp1)) {
                              Dbl_increment(opnd3p1,opnd3p2);
                        }
                        break;
                  case ROUNDMINUS: 
                        if (Dbl_isone_sign(resultp1)) {
                              Dbl_increment(opnd3p1,opnd3p2);
                        }
                        break;
                  case ROUNDNEAREST:
                        if (guardbit && (stickybit || 
                            Dbl_isone_lowmantissap2(opnd3p2))) {
                                    Dbl_increment(opnd3p1,opnd3p2);
                        }
                        break;
                  }
                  if (is_tiny) Set_underflowflag();
                }
            Dbl_set_exponentmantissa(resultp1,resultp2,opnd3p1,opnd3p2);
      }
      else Dbl_set_exponent(resultp1,dest_exponent);
      Dbl_copytoptr(resultp1,resultp2,dstptr);

      /* check for inexact */
      if (inexact) {
            if (Is_inexacttrap_enabled()) return(INEXACTEXCEPTION);
            else Set_inexactflag();
      }
      return(NOEXCEPTION);
}

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