arch/parisc/math-emu/sfsqrt.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/sfsqrt.c              $Revision: 1.1 $
  26  *
  27  *  Purpose:
  28  *      Single Floating-point Square Root
  29  *
  30  *  External Interfaces:
  31  *      sgl_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 "sgl_float.h"
  44
  45 /*
  46  *  Single Floating-point Square Root
  47  */
  48
  49 /*ARGSUSED*/
  50 unsigned int
  51 sgl_fsqrt(
  52     sgl_floating_point *srcptr,
  53     unsigned int *nullptr,
  54     sgl_floating_point *dstptr,
  55     unsigned int *status)
  56 {
  57         register unsigned int src, result;
  58         register int src_exponent;
  59         register unsigned int newbit, sum;
  60         register boolean guardbit = FALSE, even_exponent;
  61
  62         src = *srcptr;
  63         /*
  64          * check source operand for NaN or infinity
  65          */
  66         if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
  67                 /*
  68                  * is signaling NaN?
  69                  */
  70                 if (Sgl_isone_signaling(src)) {
  71                         /* trap if INVALIDTRAP enabled */
  72                         if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
  73                         /* make NaN quiet */
  74                         Set_invalidflag();
  75                         Sgl_set_quiet(src);
  76                 }
  77                 /*
  78                  * Return quiet NaN or positive infinity.
  79                  *  Fall through to negative test if negative infinity.
  80                  */
  81                 if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
  82                         *dstptr = src;
  83                         return(NOEXCEPTION);
  84                 }
  85         }
  86
  87         /*
  88          * check for zero source operand
  89          */
  90         if (Sgl_iszero_exponentmantissa(src)) {
  91                 *dstptr = src;
  92                 return(NOEXCEPTION);
  93         }
  94
  95         /*
  96          * check for negative source operand
  97          */
  98         if (Sgl_isone_sign(src)) {
  99                 /* trap if INVALIDTRAP enabled */
 100                 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
 101                 /* make NaN quiet */
 102                 Set_invalidflag();
 103                 Sgl_makequietnan(src);
 104                 *dstptr = src;
 105                 return(NOEXCEPTION);
 106         }
 107
 108         /*
 109          * Generate result
 110          */
 111         if (src_exponent > 0) {
 112                 even_exponent = Sgl_hidden(src);
 113                 Sgl_clear_signexponent_set_hidden(src);
 114         }
 115         else {
 116                 /* normalize operand */
 117                 Sgl_clear_signexponent(src);
 118                 src_exponent++;
 119                 Sgl_normalize(src,src_exponent);
 120                 even_exponent = src_exponent & 1;
 121         }
 122         if (even_exponent) {
 123                 /* exponent is even */
 124                 /* Add comment here.  Explain why odd exponent needs correction */
 125                 Sgl_leftshiftby1(src);
 126         }
 127         /*
 128          * Add comment here.  Explain following algorithm.
 129          *
 130          * Trust me, it works.
 131          *
 132          */
 133         Sgl_setzero(result);
 134         newbit = 1 << SGL_P;
 135         while (newbit && Sgl_isnotzero(src)) {
 136                 Sgl_addition(result,newbit,sum);
 137                 if(sum <= Sgl_all(src)) {
 138                         /* update result */
 139                         Sgl_addition(result,(newbit<<1),result);
 140                         Sgl_subtract(src,sum,src);
 141                 }
 142                 Sgl_rightshiftby1(newbit);
 143                 Sgl_leftshiftby1(src);
 144         }
 145         /* correct exponent for pre-shift */
 146         if (even_exponent) {
 147                 Sgl_rightshiftby1(result);
 148         }
 149
 150         /* check for inexact */
 151         if (Sgl_isnotzero(src)) {
 152                 if (!even_exponent && Sgl_islessthan(result,src))
 153                         Sgl_increment(result);
 154                 guardbit = Sgl_lowmantissa(result);
 155                 Sgl_rightshiftby1(result);
 156
 157                 /*  now round result  */
 158                 switch (Rounding_mode()) {
 159                 case ROUNDPLUS:
 160                      Sgl_increment(result);
 161                      break;
 162                 case ROUNDNEAREST:
 163                      /* stickybit is always true, so guardbit
 164                       * is enough to determine rounding */
 165                      if (guardbit) {
 166                         Sgl_increment(result);
 167                      }
 168                      break;
 169                 }
 170                 /* increment result exponent by 1 if mantissa overflowed */
 171                 if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
 172
 173                 if (Is_inexacttrap_enabled()) {
 174                         Sgl_set_exponent(result,
 175                          ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
 176                         *dstptr = result;
 177                         return(INEXACTEXCEPTION);
 178                 }
 179                 else Set_inexactflag();
 180         }
 181         else {
 182                 Sgl_rightshiftby1(result);
 183         }
 184         Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
 185         *dstptr = result;
 186         return(NOEXCEPTION);
 187 }