LXR linux/arch/mips/math-emu/dp

   1/* IEEE754 floating point arithmetic
   2 * double precision: common utilities
   3 */
   4/*
   5 * MIPS floating point support
   6 * Copyright (C) 1994-2000 Algorithmics Ltd.
   7 * http://www.algor.co.uk
   8 *
   9 * ########################################################################
  10 *
  11 *  This program is free software; you can distribute it and/or modify it
  12 *  under the terms of the GNU General Public License (Version 2) as
  13 *  published by the Free Software Foundation.
  14 *
  15 *  This program is distributed in the hope it will be useful, but WITHOUT
  16 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  17 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  18 *  for more details.
  19 *
  20 *  You should have received a copy of the GNU General Public License along
  21 *  with this program; if not, write to the Free Software Foundation, Inc.,
  22 *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
  23 *
  24 * ########################################################################
  25 */
  26
  27
  28#include "ieee754dp.h"
  29
  30ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y)
  31{
  32        COMPXDP;
  33        COMPYDP;
  34
  35        EXPLODEXDP;
  36        EXPLODEYDP;
  37
  38        CLEARCX;
  39
  40        FLUSHXDP;
  41        FLUSHYDP;
  42
  43        switch (CLPAIR(xc, yc)) {
  44        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
  45        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
  46        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
  47        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
  48        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
  49        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
  50        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
  51        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
  52        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
  53        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
  54        case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
  55                SETCX(IEEE754_INVALID_OPERATION);
  56                return ieee754dp_nanxcpt(ieee754dp_indef(), "sub", x, y);
  57
  58        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
  59        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
  60        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
  61        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
  62                return y;
  63
  64        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
  65        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
  66        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
  67        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
  68        case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
  69                return x;
  70
  71
  72                /* Infinity handling
  73                 */
  74
  75        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
  76                if (xs != ys)
  77                        return x;
  78                SETCX(IEEE754_INVALID_OPERATION);
  79                return ieee754dp_xcpt(ieee754dp_indef(), "sub", x, y);
  80
  81        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
  82        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
  83        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
  84                return ieee754dp_inf(ys ^ 1);
  85
  86        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
  87        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
  88        case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
  89                return x;
  90
  91                /* Zero handling
  92                 */
  93
  94        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
  95                if (xs != ys)
  96                        return x;
  97                else
  98                        return ieee754dp_zero(ieee754_csr.rm ==
  99                                              IEEE754_RD);
 100
 101        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
 102        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
 103                return x;
 104
 105        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
 106        case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
 107                /* quick fix up */
 108                DPSIGN(y) ^= 1;
 109                return y;
 110
 111        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
 112                DPDNORMX;
 113                /* FAAL THOROUGH */
 114
 115        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
 116                /* normalize ym,ye */
 117                DPDNORMY;
 118                break;
 119
 120        case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
 121                /* normalize xm,xe */
 122                DPDNORMX;
 123                break;
 124
 125        case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
 126                break;
 127        }
 128        /* flip sign of y and handle as add */
 129        ys ^= 1;
 130
 131        assert(xm & DP_HIDDEN_BIT);
 132        assert(ym & DP_HIDDEN_BIT);
 133
 134
 135        /* provide guard,round and stick bit dpace */
 136        xm <<= 3;
 137        ym <<= 3;
 138
 139        if (xe > ye) {
 140                /* have to shift y fraction right to align
 141                 */
 142                int s = xe - ye;
 143                ym = XDPSRS(ym, s);
 144                ye += s;
 145        } else if (ye > xe) {
 146                /* have to shift x fraction right to align
 147                 */
 148                int s = ye - xe;
 149                xm = XDPSRS(xm, s);
 150                xe += s;
 151        }
 152        assert(xe == ye);
 153        assert(xe <= DP_EMAX);
 154
 155        if (xs == ys) {
 156                /* generate 28 bit result of adding two 27 bit numbers
 157                 */
 158                xm = xm + ym;
 159                xe = xe;
 160                xs = xs;
 161
 162                if (xm >> (DP_MBITS + 1 + 3)) { /* carry out */
 163                        xm = XDPSRS1(xm);       /* shift preserving sticky */
 164                        xe++;
 165                }
 166        } else {
 167                if (xm >= ym) {
 168                        xm = xm - ym;
 169                        xe = xe;
 170                        xs = xs;
 171                } else {
 172                        xm = ym - xm;
 173                        xe = xe;
 174                        xs = ys;
 175                }
 176                if (xm == 0) {
 177                        if (ieee754_csr.rm == IEEE754_RD)
 178                                return ieee754dp_zero(1);       /* round negative inf. => sign = -1 */
 179                        else
 180                                return ieee754dp_zero(0);       /* other round modes   => sign = 1 */
 181                }
 182
 183                /* normalize to rounding precision
 184                 */
 185                while ((xm >> (DP_MBITS + 3)) == 0) {
 186                        xm <<= 1;
 187                        xe--;
 188                }
 189        }
 190        DPNORMRET2(xs, xe, xm, "sub", x, y);
 191}
 192