LXR linux/arch/mips/math-emu/ieee754sp.c

   1/* IEEE754 floating point arithmetic
   2 * single precision
   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 "ieee754sp.h"
  29
  30int ieee754sp_class(ieee754sp x)
  31{
  32        COMPXSP;
  33        EXPLODEXSP;
  34        return xc;
  35}
  36
  37int ieee754sp_isnan(ieee754sp x)
  38{
  39        return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
  40}
  41
  42int ieee754sp_issnan(ieee754sp x)
  43{
  44        assert(ieee754sp_isnan(x));
  45        return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
  46}
  47
  48
  49ieee754sp ieee754sp_xcpt(ieee754sp r, const char *op, ...)
  50{
  51        struct ieee754xctx ax;
  52
  53        if (!TSTX())
  54                return r;
  55
  56        ax.op = op;
  57        ax.rt = IEEE754_RT_SP;
  58        ax.rv.sp = r;
  59        va_start(ax.ap, op);
  60        ieee754_xcpt(&ax);
  61        va_end(ax.ap);
  62        return ax.rv.sp;
  63}
  64
  65ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
  66{
  67        struct ieee754xctx ax;
  68
  69        assert(ieee754sp_isnan(r));
  70
  71        if (!ieee754sp_issnan(r))       /* QNAN does not cause invalid op !! */
  72                return r;
  73
  74        if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
  75                /* not enabled convert to a quiet NaN */
  76                SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
  77                if (ieee754sp_isnan(r))
  78                        return r;
  79                else
  80                        return ieee754sp_indef();
  81        }
  82
  83        ax.op = op;
  84        ax.rt = 0;
  85        ax.rv.sp = r;
  86        va_start(ax.ap, op);
  87        ieee754_xcpt(&ax);
  88        va_end(ax.ap);
  89        return ax.rv.sp;
  90}
  91
  92ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
  93{
  94        assert(ieee754sp_isnan(x));
  95        assert(ieee754sp_isnan(y));
  96
  97        if (SPMANT(x) > SPMANT(y))
  98                return x;
  99        else
 100                return y;
 101}
 102
 103
 104static unsigned get_rounding(int sn, unsigned xm)
 105{
 106        /* inexact must round of 3 bits
 107         */
 108        if (xm & (SP_MBIT(3) - 1)) {
 109                switch (ieee754_csr.rm) {
 110                case IEEE754_RZ:
 111                        break;
 112                case IEEE754_RN:
 113                        xm += 0x3 + ((xm >> 3) & 1);
 114                        /* xm += (xm&0x8)?0x4:0x3 */
 115                        break;
 116                case IEEE754_RU:        /* toward +Infinity */
 117                        if (!sn)        /* ?? */
 118                                xm += 0x8;
 119                        break;
 120                case IEEE754_RD:        /* toward -Infinity */
 121                        if (sn) /* ?? */
 122                                xm += 0x8;
 123                        break;
 124                }
 125        }
 126        return xm;
 127}
 128
 129
 130/* generate a normal/denormal number with over,under handling
 131 * sn is sign
 132 * xe is an unbiased exponent
 133 * xm is 3bit extended precision value.
 134 */
 135ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 136{
 137        assert(xm);             /* we don't gen exact zeros (probably should) */
 138
 139        assert((xm >> (SP_MBITS + 1 + 3)) == 0);        /* no execess */
 140        assert(xm & (SP_HIDDEN_BIT << 3));
 141
 142        if (xe < SP_EMIN) {
 143                /* strip lower bits */
 144                int es = SP_EMIN - xe;
 145
 146                if (ieee754_csr.nod) {
 147                        SETCX(IEEE754_UNDERFLOW);
 148                        SETCX(IEEE754_INEXACT);
 149
 150                        switch(ieee754_csr.rm) {
 151                        case IEEE754_RN:
 152                                return ieee754sp_zero(sn);
 153                        case IEEE754_RZ:
 154                                return ieee754sp_zero(sn);
 155                        case IEEE754_RU:      /* toward +Infinity */
 156                                if(sn == 0)
 157                                        return ieee754sp_min(0);
 158                                else
 159                                        return ieee754sp_zero(1);
 160                        case IEEE754_RD:      /* toward -Infinity */
 161                                if(sn == 0)
 162                                        return ieee754sp_zero(0);
 163                                else
 164                                        return ieee754sp_min(1);
 165                        }
 166                }
 167
 168                if (xe == SP_EMIN - 1
 169                                && get_rounding(sn, xm) >> (SP_MBITS + 1 + 3))
 170                {
 171                        /* Not tiny after rounding */
 172                        SETCX(IEEE754_INEXACT);
 173                        xm = get_rounding(sn, xm);
 174                        xm >>= 1;
 175                        /* Clear grs bits */
 176                        xm &= ~(SP_MBIT(3) - 1);
 177                        xe++;
 178                }
 179                else {
 180                        /* sticky right shift es bits
 181                         */
 182                        SPXSRSXn(es);
 183                        assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
 184                        assert(xe == SP_EMIN);
 185                }
 186        }
 187        if (xm & (SP_MBIT(3) - 1)) {
 188                SETCX(IEEE754_INEXACT);
 189                if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
 190                        SETCX(IEEE754_UNDERFLOW);
 191                }
 192
 193                /* inexact must round of 3 bits
 194                 */
 195                xm = get_rounding(sn, xm);
 196                /* adjust exponent for rounding add overflowing
 197                 */
 198                if (xm >> (SP_MBITS + 1 + 3)) {
 199                        /* add causes mantissa overflow */
 200                        xm >>= 1;
 201                        xe++;
 202                }
 203        }
 204        /* strip grs bits */
 205        xm >>= 3;
 206
 207        assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 208        assert(xe >= SP_EMIN);
 209
 210        if (xe > SP_EMAX) {
 211                SETCX(IEEE754_OVERFLOW);
 212                SETCX(IEEE754_INEXACT);
 213                /* -O can be table indexed by (rm,sn) */
 214                switch (ieee754_csr.rm) {
 215                case IEEE754_RN:
 216                        return ieee754sp_inf(sn);
 217                case IEEE754_RZ:
 218                        return ieee754sp_max(sn);
 219                case IEEE754_RU:        /* toward +Infinity */
 220                        if (sn == 0)
 221                                return ieee754sp_inf(0);
 222                        else
 223                                return ieee754sp_max(1);
 224                case IEEE754_RD:        /* toward -Infinity */
 225                        if (sn == 0)
 226                                return ieee754sp_max(0);
 227                        else
 228                                return ieee754sp_inf(1);
 229                }
 230        }
 231        /* gen norm/denorm/zero */
 232
 233        if ((xm & SP_HIDDEN_BIT) == 0) {
 234                /* we underflow (tiny/zero) */
 235                assert(xe == SP_EMIN);
 236                if (ieee754_csr.mx & IEEE754_UNDERFLOW)
 237                        SETCX(IEEE754_UNDERFLOW);
 238                return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
 239        } else {
 240                assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 241                assert(xm & SP_HIDDEN_BIT);
 242
 243                return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
 244        }
 245}
 246