arch/mips/math-emu/dp_sub.c

   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
  30 ieee754dp 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                 /* FALL THROUGH */
 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 }