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