LXR linux/arch/mips/math-emu/ieee754dp.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
  29int ieee754dp_class(ieee754dp x)
  30{
  31        COMPXDP;
  32        EXPLODEXDP;
  33        return xc;
  34}
  35
  36int ieee754dp_isnan(ieee754dp x)
  37{
  38        return ieee754dp_class(x) >= IEEE754_CLASS_SNAN;
  39}
  40
  41int ieee754dp_issnan(ieee754dp x)
  42{
  43        assert(ieee754dp_isnan(x));
  44        return ((DPMANT(x) & DP_MBIT(DP_MBITS-1)) == DP_MBIT(DP_MBITS-1));
  45}
  46
  47
  48ieee754dp ieee754dp_xcpt(ieee754dp r, const char *op, ...)
  49{
  50        struct ieee754xctx ax;
  51        if (!TSTX())
  52                return r;
  53
  54        ax.op = op;
  55        ax.rt = IEEE754_RT_DP;
  56        ax.rv.dp = r;
  57        va_start(ax.ap, op);
  58        ieee754_xcpt(&ax);
  59        va_end(ax.ap);
  60        return ax.rv.dp;
  61}
  62
  63ieee754dp ieee754dp_nanxcpt(ieee754dp r, const char *op, ...)
  64{
  65        struct ieee754xctx ax;
  66
  67        assert(ieee754dp_isnan(r));
  68
  69        if (!ieee754dp_issnan(r))       /* QNAN does not cause invalid op !! */
  70                return r;
  71
  72        if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
  73                /* not enabled convert to a quiet NaN */
  74                DPMANT(r) &= (~DP_MBIT(DP_MBITS-1));
  75                if (ieee754dp_isnan(r))
  76                        return r;
  77                else
  78                        return ieee754dp_indef();
  79        }
  80
  81        ax.op = op;
  82        ax.rt = 0;
  83        ax.rv.dp = r;
  84        va_start(ax.ap, op);
  85        ieee754_xcpt(&ax);
  86        va_end(ax.ap);
  87        return ax.rv.dp;
  88}
  89
  90ieee754dp ieee754dp_bestnan(ieee754dp x, ieee754dp y)
  91{
  92        assert(ieee754dp_isnan(x));
  93        assert(ieee754dp_isnan(y));
  94
  95        if (DPMANT(x) > DPMANT(y))
  96                return x;
  97        else
  98                return y;
  99}
 100
 101
 102static u64 get_rounding(int sn, u64 xm)
 103{
 104        /* inexact must round of 3 bits
 105         */
 106        if (xm & (DP_MBIT(3) - 1)) {
 107                switch (ieee754_csr.rm) {
 108                case IEEE754_RZ:
 109                        break;
 110                case IEEE754_RN:
 111                        xm += 0x3 + ((xm >> 3) & 1);
 112                        /* xm += (xm&0x8)?0x4:0x3 */
 113                        break;
 114                case IEEE754_RU:        /* toward +Infinity */
 115                        if (!sn)        /* ?? */
 116                                xm += 0x8;
 117                        break;
 118                case IEEE754_RD:        /* toward -Infinity */
 119                        if (sn) /* ?? */
 120                                xm += 0x8;
 121                        break;
 122                }
 123        }
 124        return xm;
 125}
 126
 127
 128/* generate a normal/denormal number with over,under handling
 129 * sn is sign
 130 * xe is an unbiased exponent
 131 * xm is 3bit extended precision value.
 132 */
 133ieee754dp ieee754dp_format(int sn, int xe, u64 xm)
 134{
 135        assert(xm);             /* we don't gen exact zeros (probably should) */
 136
 137        assert((xm >> (DP_MBITS + 1 + 3)) == 0);        /* no execess */
 138        assert(xm & (DP_HIDDEN_BIT << 3));
 139
 140        if (xe < DP_EMIN) {
 141                /* strip lower bits */
 142                int es = DP_EMIN - xe;
 143
 144                if (ieee754_csr.nod) {
 145                        SETCX(IEEE754_UNDERFLOW);
 146                        SETCX(IEEE754_INEXACT);
 147
 148                        switch(ieee754_csr.rm) {
 149                        case IEEE754_RN:
 150                        case IEEE754_RZ:
 151                                return ieee754dp_zero(sn);
 152                        case IEEE754_RU:    /* toward +Infinity */
 153                                if(sn == 0)
 154                                        return ieee754dp_min(0);
 155                                else
 156                                        return ieee754dp_zero(1);
 157                        case IEEE754_RD:    /* toward -Infinity */
 158                                if(sn == 0)
 159                                        return ieee754dp_zero(0);
 160                                else
 161                                        return ieee754dp_min(1);
 162                        }
 163                }
 164
 165                if (xe == DP_EMIN - 1
 166                                && get_rounding(sn, xm) >> (DP_MBITS + 1 + 3))
 167                {
 168                        /* Not tiny after rounding */
 169                        SETCX(IEEE754_INEXACT);
 170                        xm = get_rounding(sn, xm);
 171                        xm >>= 1;
 172                        /* Clear grs bits */
 173                        xm &= ~(DP_MBIT(3) - 1);
 174                        xe++;
 175                }
 176                else {
 177                        /* sticky right shift es bits
 178                         */
 179                        xm = XDPSRS(xm, es);
 180                        xe += es;
 181                        assert((xm & (DP_HIDDEN_BIT << 3)) == 0);
 182                        assert(xe == DP_EMIN);
 183                }
 184        }
 185        if (xm & (DP_MBIT(3) - 1)) {
 186                SETCX(IEEE754_INEXACT);
 187                if ((xm & (DP_HIDDEN_BIT << 3)) == 0) {
 188                        SETCX(IEEE754_UNDERFLOW);
 189                }
 190
 191                /* inexact must round of 3 bits
 192                 */
 193                xm = get_rounding(sn, xm);
 194                /* adjust exponent for rounding add overflowing
 195                 */
 196                if (xm >> (DP_MBITS + 3 + 1)) {
 197                        /* add causes mantissa overflow */
 198                        xm >>= 1;
 199                        xe++;
 200                }
 201        }
 202        /* strip grs bits */
 203        xm >>= 3;
 204
 205        assert((xm >> (DP_MBITS + 1)) == 0);    /* no execess */
 206        assert(xe >= DP_EMIN);
 207
 208        if (xe > DP_EMAX) {
 209                SETCX(IEEE754_OVERFLOW);
 210                SETCX(IEEE754_INEXACT);
 211                /* -O can be table indexed by (rm,sn) */
 212                switch (ieee754_csr.rm) {
 213                case IEEE754_RN:
 214                        return ieee754dp_inf(sn);
 215                case IEEE754_RZ:
 216                        return ieee754dp_max(sn);
 217                case IEEE754_RU:        /* toward +Infinity */
 218                        if (sn == 0)
 219                                return ieee754dp_inf(0);
 220                        else
 221                                return ieee754dp_max(1);
 222                case IEEE754_RD:        /* toward -Infinity */
 223                        if (sn == 0)
 224                                return ieee754dp_max(0);
 225                        else
 226                                return ieee754dp_inf(1);
 227                }
 228        }
 229        /* gen norm/denorm/zero */
 230
 231        if ((xm & DP_HIDDEN_BIT) == 0) {
 232                /* we underflow (tiny/zero) */
 233                assert(xe == DP_EMIN);
 234                if (ieee754_csr.mx & IEEE754_UNDERFLOW)
 235                        SETCX(IEEE754_UNDERFLOW);
 236                return builddp(sn, DP_EMIN - 1 + DP_EBIAS, xm);
 237        } else {
 238                assert((xm >> (DP_MBITS + 1)) == 0);    /* no execess */
 239                assert(xm & DP_HIDDEN_BIT);
 240
 241                return builddp(sn, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
 242        }
 243}
 244