LXR linux/arch/parisc/math-emu/dfsqrt.c

   1/*
   2 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
   3 *
   4 * Floating-point emulation code
   5 *  Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
   6 *
   7 *    This program is free software; you can redistribute it and/or modify
   8 *    it under the terms of the GNU General Public License as published by
   9 *    the Free Software Foundation; either version 2, or (at your option)
  10 *    any later version.
  11 *
  12 *    This program is distributed in the hope that it will be useful,
  13 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 *    GNU General Public License for more details.
  16 *
  17 *    You should have received a copy of the GNU General Public License
  18 *    along with this program; if not, write to the Free Software
  19 *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20 */
  21/*
  22 * BEGIN_DESC
  23 *
  24 *  File:
  25 *      @(#)    pa/spmath/dfsqrt.c              $Revision: 1.1 $
  26 *
  27 *  Purpose:
  28 *      Double Floating-point Square Root
  29 *
  30 *  External Interfaces:
  31 *      dbl_fsqrt(srcptr,nullptr,dstptr,status)
  32 *
  33 *  Internal Interfaces:
  34 *
  35 *  Theory:
  36 *      <<please update with a overview of the operation of this file>>
  37 *
  38 * END_DESC
  39*/
  40
  41
  42#include "float.h"
  43#include "dbl_float.h"
  44
  45/*
  46 *  Double Floating-point Square Root
  47 */
  48
  49/*ARGSUSED*/
  50unsigned int
  51dbl_fsqrt(
  52            dbl_floating_point *srcptr,
  53            unsigned int *nullptr,
  54            dbl_floating_point *dstptr,
  55            unsigned int *status)
  56{
  57        register unsigned int srcp1, srcp2, resultp1, resultp2;
  58        register unsigned int newbitp1, newbitp2, sump1, sump2;
  59        register int src_exponent;
  60        register boolean guardbit = FALSE, even_exponent;
  61
  62        Dbl_copyfromptr(srcptr,srcp1,srcp2);
  63        /*
  64         * check source operand for NaN or infinity
  65         */
  66        if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) {
  67                /*
  68                 * is signaling NaN?
  69                 */
  70                if (Dbl_isone_signaling(srcp1)) {
  71                        /* trap if INVALIDTRAP enabled */
  72                        if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
  73                        /* make NaN quiet */
  74                        Set_invalidflag();
  75                        Dbl_set_quiet(srcp1);
  76                }
  77                /*
  78                 * Return quiet NaN or positive infinity.
  79                 *  Fall through to negative test if negative infinity.
  80                 */
  81                if (Dbl_iszero_sign(srcp1) || 
  82                    Dbl_isnotzero_mantissa(srcp1,srcp2)) {
  83                        Dbl_copytoptr(srcp1,srcp2,dstptr);
  84                        return(NOEXCEPTION);
  85                }
  86        }
  87
  88        /*
  89         * check for zero source operand
  90         */
  91        if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) {
  92                Dbl_copytoptr(srcp1,srcp2,dstptr);
  93                return(NOEXCEPTION);
  94        }
  95
  96        /*
  97         * check for negative source operand 
  98         */
  99        if (Dbl_isone_sign(srcp1)) {
 100                /* trap if INVALIDTRAP enabled */
 101                if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
 102                /* make NaN quiet */
 103                Set_invalidflag();
 104                Dbl_makequietnan(srcp1,srcp2);
 105                Dbl_copytoptr(srcp1,srcp2,dstptr);
 106                return(NOEXCEPTION);
 107        }
 108
 109        /*
 110         * Generate result
 111         */
 112        if (src_exponent > 0) {
 113                even_exponent = Dbl_hidden(srcp1);
 114                Dbl_clear_signexponent_set_hidden(srcp1);
 115        }
 116        else {
 117                /* normalize operand */
 118                Dbl_clear_signexponent(srcp1);
 119                src_exponent++;
 120                Dbl_normalize(srcp1,srcp2,src_exponent);
 121                even_exponent = src_exponent & 1;
 122        }
 123        if (even_exponent) {
 124                /* exponent is even */
 125                /* Add comment here.  Explain why odd exponent needs correction */
 126                Dbl_leftshiftby1(srcp1,srcp2);
 127        }
 128        /*
 129         * Add comment here.  Explain following algorithm.
 130         * 
 131         * Trust me, it works.
 132         *
 133         */
 134        Dbl_setzero(resultp1,resultp2);
 135        Dbl_allp1(newbitp1) = 1 << (DBL_P - 32);
 136        Dbl_setzero_mantissap2(newbitp2);
 137        while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) {
 138                Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2);
 139                if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) {
 140                        Dbl_leftshiftby1(newbitp1,newbitp2);
 141                        /* update result */
 142                        Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,
 143                         resultp1,resultp2);  
 144                        Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2);
 145                        Dbl_rightshiftby2(newbitp1,newbitp2);
 146                }
 147                else {
 148                        Dbl_rightshiftby1(newbitp1,newbitp2);
 149                }
 150                Dbl_leftshiftby1(srcp1,srcp2);
 151        }
 152        /* correct exponent for pre-shift */
 153        if (even_exponent) {
 154                Dbl_rightshiftby1(resultp1,resultp2);
 155        }
 156
 157        /* check for inexact */
 158        if (Dbl_isnotzero(srcp1,srcp2)) {
 159                if (!even_exponent && Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) {
 160                        Dbl_increment(resultp1,resultp2);
 161                }
 162                guardbit = Dbl_lowmantissap2(resultp2);
 163                Dbl_rightshiftby1(resultp1,resultp2);
 164
 165                /*  now round result  */
 166                switch (Rounding_mode()) {
 167                case ROUNDPLUS:
 168                     Dbl_increment(resultp1,resultp2);
 169                     break;
 170                case ROUNDNEAREST:
 171                     /* stickybit is always true, so guardbit 
 172                      * is enough to determine rounding */
 173                     if (guardbit) {
 174                            Dbl_increment(resultp1,resultp2);
 175                     }
 176                     break;
 177                }
 178                /* increment result exponent by 1 if mantissa overflowed */
 179                if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2;
 180
 181                if (Is_inexacttrap_enabled()) {
 182                        Dbl_set_exponent(resultp1,
 183                         ((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
 184                        Dbl_copytoptr(resultp1,resultp2,dstptr);
 185                        return(INEXACTEXCEPTION);
 186                }
 187                else Set_inexactflag();
 188        }
 189        else {
 190                Dbl_rightshiftby1(resultp1,resultp2);
 191        }
 192        Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
 193        Dbl_copytoptr(resultp1,resultp2,dstptr);
 194        return(NOEXCEPTION);
 195}
 196