LXR linux/arch/mips/math-emu/sp

   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
  29ieee754sp 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}
 184