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
  29 int ieee754dp_class(ieee754dp x)
  30 {
  31         COMPXDP;
  32         EXPLODEXDP;
  33         return xc;
  34 }
  35
  36 int ieee754dp_isnan(ieee754dp x)
  37 {
  38         return ieee754dp_class(x) >= IEEE754_CLASS_SNAN;
  39 }
  40
  41 int 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
  48 ieee754dp 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
  63 ieee754dp 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
  90 ieee754dp 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
 102 static 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  */
 133 ieee754dp 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 }