LXR linux/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*/
  50unsigned int
  51sgl_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}
 188