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
  30 int ieee754sp_class(ieee754sp x)
  31 {
  32         COMPXSP;
  33         EXPLODEXSP;
  34         return xc;
  35 }
  36
  37 int ieee754sp_isnan(ieee754sp x)
  38 {
  39         return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
  40 }
  41
  42 int ieee754sp_issnan(ieee754sp x)
  43 {
  44         assert(ieee754sp_isnan(x));
  45         return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
  46 }
  47
  48
  49 ieee754sp 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         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         return ax.rv.sp;
  88 }
  89
  90 ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
  91 {
  92         assert(ieee754sp_isnan(x));
  93         assert(ieee754sp_isnan(y));
  94
  95         if (SPMANT(x) > SPMANT(y))
  96                 return x;
  97         else
  98                 return y;
  99 }
 100
 101
 102 static unsigned get_rounding(int sn, unsigned xm)
 103 {
 104         /* inexact must round of 3 bits
 105          */
 106         if (xm & (SP_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 ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 134 {
 135         assert(xm);             /* we don't gen exact zeros (probably should) */
 136
 137         assert((xm >> (SP_MBITS + 1 + 3)) == 0);        /* no execess */
 138         assert(xm & (SP_HIDDEN_BIT << 3));
 139
 140         if (xe < SP_EMIN) {
 141                 /* strip lower bits */
 142                 int es = SP_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                                 return ieee754sp_zero(sn);
 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 }