arch/mips/math-emu/sp_sub.c

   1 /* IEEE754 floating point arithmetic
   2  * single precision
   3  */
   4 /*
   5  * MIPS floating point support
   6  * Copyright (C) 1994-2000 Algorithmics Ltd.
   7  *
   8  *  This program is free software; you can distribute it and/or modify it
   9  *  under the terms of the GNU General Public License (Version 2) as
  10  *  published by the Free Software Foundation.
  11  *
  12  *  This program is distributed in the hope it will be useful, but WITHOUT
  13  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15  *  for more details.
  16  *
  17  *  You should have received a copy of the GNU General Public License along
  18  *  with this program; if not, write to the Free Software Foundation, Inc.,
  19  *  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA.
  20  */
  21
  22 #include "ieee754sp.h"
  23
  24 union ieee754sp ieee754sp_sub(union ieee754sp x, union ieee754sp y)
  25 {
  26         int s;
  27
  28         COMPXSP;
  29         COMPYSP;
  30
  31         EXPLODEXSP;
  32         EXPLODEYSP;
  33
  34         ieee754_clearcx();
  35
  36         FLUSHXSP;
  37         FLUSHYSP;
  38
  39         switch (CLPAIR(xc, yc)) {
  40         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
  41         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
  42         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
  43         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
  44         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
  45                 return ieee754sp_nanxcpt(y);
  46
  47         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
  48         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
  49         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
  50         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
  51         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
  52         case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
  53                 return ieee754sp_nanxcpt(x);
  54
  55         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
  56         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
  57         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
  58         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
  59                 return y;
  60
  61         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
  62         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
  63         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
  64         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
  65         case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
  66                 return x;
  67
  68
  69         /*
  70          * Infinity handling
  71          */
  72         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
  73                 if (xs != ys)
  74                         return x;
  75                 ieee754_setcx(IEEE754_INVALID_OPERATION);
  76                 return ieee754sp_indef();
  77
  78         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
  79         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
  80         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
  81                 return ieee754sp_inf(ys ^ 1);
  82
  83         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
  84         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
  85         case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
  86                 return x;
  87
  88         /*
  89          * Zero handling
  90          */
  91         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
  92                 if (xs != ys)
  93                         return x;
  94                 else
  95                         return ieee754sp_zero(ieee754_csr.rm == FPU_CSR_RD);
  96
  97         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
  98         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
  99                 return x;
 100
 101         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
 102         case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
 103                 /* quick fix up */
 104                 SPSIGN(y) ^= 1;
 105                 return y;
 106
 107         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
 108                 SPDNORMX;
 109                 /* fall through */
 110
 111         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
 112                 SPDNORMY;
 113                 break;
 114
 115         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
 116                 SPDNORMX;
 117                 break;
 118
 119         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
 120                 break;
 121         }
 122         /* flip sign of y and handle as add */
 123         ys ^= 1;
 124
 125         assert(xm & SP_HIDDEN_BIT);
 126         assert(ym & SP_HIDDEN_BIT);
 127
 128
 129         /* provide guard,round and stick bit space */
 130         xm <<= 3;
 131         ym <<= 3;
 132
 133         if (xe > ye) {
 134                 /*
 135                  * have to shift y fraction right to align
 136                  */
 137                 s = xe - ye;
 138                 ym = XSPSRS(ym, s);
 139                 ye += s;
 140         } else if (ye > xe) {
 141                 /*
 142                  * have to shift x fraction right to align
 143                  */
 144                 s = ye - xe;
 145                 xm = XSPSRS(xm, s);
 146                 xe += s;
 147         }
 148         assert(xe == ye);
 149         assert(xe <= SP_EMAX);
 150
 151         if (xs == ys) {
 152                 /* generate 28 bit result of adding two 27 bit numbers
 153                  */
 154                 xm = xm + ym;
 155
 156                 if (xm >> (SP_FBITS + 1 + 3)) { /* carry out */
 157                         SPXSRSX1();     /* shift preserving sticky */
 158                 }
 159         } else {
 160                 if (xm >= ym) {
 161                         xm = xm - ym;
 162                 } else {
 163                         xm = ym - xm;
 164                         xs = ys;
 165                 }
 166                 if (xm == 0) {
 167                         if (ieee754_csr.rm == FPU_CSR_RD)
 168                                 return ieee754sp_zero(1);       /* round negative inf. => sign = -1 */
 169                         else
 170                                 return ieee754sp_zero(0);       /* other round modes   => sign = 1 */
 171                 }
 172                 /* normalize to rounding precision
 173                  */
 174                 while ((xm >> (SP_FBITS + 3)) == 0) {
 175                         xm <<= 1;
 176                         xe--;
 177                 }
 178         }
 179
 180         return ieee754sp_format(xs, xe, xm);
 181 }