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  *
   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
  29 ieee754dp 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 }