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