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  *
   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
  29 int ieee754sp_class(ieee754sp x)
  30 {
  31         COMPXSP;
  32         EXPLODEXSP;
  33         return xc;
  34 }
  35
  36 int ieee754sp_isnan(ieee754sp x)
  37 {
  38         return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
  39 }
  40
  41 int ieee754sp_issnan(ieee754sp x)
  42 {
  43         assert(ieee754sp_isnan(x));
  44         return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
  45 }
  46
  47
  48 ieee754sp ieee754sp_xcpt(ieee754sp r, const char *op, ...)
  49 {
  50         struct ieee754xctx ax;
  51
  52         if (!TSTX())
  53                 return r;
  54
  55         ax.op = op;
  56         ax.rt = IEEE754_RT_SP;
  57         ax.rv.sp = r;
  58         va_start(ax.ap, op);
  59         ieee754_xcpt(&ax);
  60         va_end(ax.ap);
  61         return ax.rv.sp;
  62 }
  63
  64 ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
  65 {
  66         struct ieee754xctx ax;
  67
  68         assert(ieee754sp_isnan(r));
  69
  70         if (!ieee754sp_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                 SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
  76                 if (ieee754sp_isnan(r))
  77                         return r;
  78                 else
  79                         return ieee754sp_indef();
  80         }
  81
  82         ax.op = op;
  83         ax.rt = 0;
  84         ax.rv.sp = r;
  85         va_start(ax.ap, op);
  86         ieee754_xcpt(&ax);
  87         va_end(ax.ap);
  88         return ax.rv.sp;
  89 }
  90
  91 ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
  92 {
  93         assert(ieee754sp_isnan(x));
  94         assert(ieee754sp_isnan(y));
  95
  96         if (SPMANT(x) > SPMANT(y))
  97                 return x;
  98         else
  99                 return y;
 100 }
 101
 102
 103 static unsigned get_rounding(int sn, unsigned xm)
 104 {
 105         /* inexact must round of 3 bits
 106          */
 107         if (xm & (SP_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 ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 135 {
 136         assert(xm);             /* we don't gen exact zeros (probably should) */
 137
 138         assert((xm >> (SP_MBITS + 1 + 3)) == 0);        /* no execess */
 139         assert(xm & (SP_HIDDEN_BIT << 3));
 140
 141         if (xe < SP_EMIN) {
 142                 /* strip lower bits */
 143                 int es = SP_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 ieee754sp_zero(sn);
 153                         case IEEE754_RU:      /* toward +Infinity */
 154                                 if(sn == 0)
 155                                         return ieee754sp_min(0);
 156                                 else
 157                                         return ieee754sp_zero(1);
 158                         case IEEE754_RD:      /* toward -Infinity */
 159                                 if(sn == 0)
 160                                         return ieee754sp_zero(0);
 161                                 else
 162                                         return ieee754sp_min(1);
 163                         }
 164                 }
 165
 166                 if (xe == SP_EMIN - 1
 167                                 && get_rounding(sn, xm) >> (SP_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 &= ~(SP_MBIT(3) - 1);
 175                         xe++;
 176                 }
 177                 else {
 178                         /* sticky right shift es bits
 179                          */
 180                         SPXSRSXn(es);
 181                         assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
 182                         assert(xe == SP_EMIN);
 183                 }
 184         }
 185         if (xm & (SP_MBIT(3) - 1)) {
 186                 SETCX(IEEE754_INEXACT);
 187                 if ((xm & (SP_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 >> (SP_MBITS + 1 + 3)) {
 197                         /* add causes mantissa overflow */
 198                         xm >>= 1;
 199                         xe++;
 200                 }
 201         }
 202         /* strip grs bits */
 203         xm >>= 3;
 204
 205         assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 206         assert(xe >= SP_EMIN);
 207
 208         if (xe > SP_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 ieee754sp_inf(sn);
 215                 case IEEE754_RZ:
 216                         return ieee754sp_max(sn);
 217                 case IEEE754_RU:        /* toward +Infinity */
 218                         if (sn == 0)
 219                                 return ieee754sp_inf(0);
 220                         else
 221                                 return ieee754sp_max(1);
 222                 case IEEE754_RD:        /* toward -Infinity */
 223                         if (sn == 0)
 224                                 return ieee754sp_max(0);
 225                         else
 226                                 return ieee754sp_inf(1);
 227                 }
 228         }
 229         /* gen norm/denorm/zero */
 230
 231         if ((xm & SP_HIDDEN_BIT) == 0) {
 232                 /* we underflow (tiny/zero) */
 233                 assert(xe == SP_EMIN);
 234                 if (ieee754_csr.mx & IEEE754_UNDERFLOW)
 235                         SETCX(IEEE754_UNDERFLOW);
 236                 return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
 237         } else {
 238                 assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 239                 assert(xm & SP_HIDDEN_BIT);
 240
 241                 return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
 242         }
 243 }