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  * ########################################################################
   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 "ieee754sp.h"
  28
  29 ieee754sp ieee754sp_sub(ieee754sp x, ieee754sp y)
  30 {
  31         COMPXSP;
  32         COMPYSP;
  33
  34         EXPLODEXSP;
  35         EXPLODEYSP;
  36
  37         CLEARCX;
  38
  39         FLUSHXSP;
  40         FLUSHYSP;
  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 ieee754sp_nanxcpt(ieee754sp_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 ieee754sp_xcpt(ieee754sp_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 ieee754sp_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 ieee754sp_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                 SPDNORMX;
 112
 113         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
 114                 SPDNORMY;
 115                 break;
 116
 117         case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
 118                 SPDNORMX;
 119                 break;
 120
 121         case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
 122                 break;
 123         }
 124         /* flip sign of y and handle as add */
 125         ys ^= 1;
 126
 127         assert(xm & SP_HIDDEN_BIT);
 128         assert(ym & SP_HIDDEN_BIT);
 129
 130
 131         /* provide guard,round and stick bit space */
 132         xm <<= 3;
 133         ym <<= 3;
 134
 135         if (xe > ye) {
 136                 /* have to shift y fraction right to align
 137                  */
 138                 int s = xe - ye;
 139                 SPXSRSYn(s);
 140         } else if (ye > xe) {
 141                 /* have to shift x fraction right to align
 142                  */
 143                 int s = ye - xe;
 144                 SPXSRSXn(s);
 145         }
 146         assert(xe == ye);
 147         assert(xe <= SP_EMAX);
 148
 149         if (xs == ys) {
 150                 /* generate 28 bit result of adding two 27 bit numbers
 151                  */
 152                 xm = xm + ym;
 153                 xe = xe;
 154                 xs = xs;
 155
 156                 if (xm >> (SP_MBITS + 1 + 3)) { /* carry out */
 157                         SPXSRSX1();     /* shift preserving sticky */
 158                 }
 159         } else {
 160                 if (xm >= ym) {
 161                         xm = xm - ym;
 162                         xe = xe;
 163                         xs = xs;
 164                 } else {
 165                         xm = ym - xm;
 166                         xe = xe;
 167                         xs = ys;
 168                 }
 169                 if (xm == 0) {
 170                         if (ieee754_csr.rm == IEEE754_RD)
 171                                 return ieee754sp_zero(1);       /* round negative inf. => sign = -1 */
 172                         else
 173                                 return ieee754sp_zero(0);       /* other round modes   => sign = 1 */
 174                 }
 175                 /* normalize to rounding precision
 176                  */
 177                 while ((xm >> (SP_MBITS + 3)) == 0) {
 178                         xm <<= 1;
 179                         xe--;
 180                 }
 181         }
 182         SPNORMRET2(xs, xe, xm, "sub", x, y);
 183 }