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         va_end(ax.ap);
  62         return ax.rv.sp;
  63 }
  64
  65 ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
  66 {
  67         struct ieee754xctx ax;
  68
  69         assert(ieee754sp_isnan(r));
  70
  71         if (!ieee754sp_issnan(r))       /* QNAN does not cause invalid op !! */
  72                 return r;
  73
  74         if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
  75                 /* not enabled convert to a quiet NaN */
  76                 SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
  77                 if (ieee754sp_isnan(r))
  78                         return r;
  79                 else
  80                         return ieee754sp_indef();
  81         }
  82
  83         ax.op = op;
  84         ax.rt = 0;
  85         ax.rv.sp = r;
  86         va_start(ax.ap, op);
  87         ieee754_xcpt(&ax);
  88         va_end(ax.ap);
  89         return ax.rv.sp;
  90 }
  91
  92 ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
  93 {
  94         assert(ieee754sp_isnan(x));
  95         assert(ieee754sp_isnan(y));
  96
  97         if (SPMANT(x) > SPMANT(y))
  98                 return x;
  99         else
 100                 return y;
 101 }
 102
 103
 104 static unsigned get_rounding(int sn, unsigned xm)
 105 {
 106         /* inexact must round of 3 bits
 107          */
 108         if (xm & (SP_MBIT(3) - 1)) {
 109                 switch (ieee754_csr.rm) {
 110                 case IEEE754_RZ:
 111                         break;
 112                 case IEEE754_RN:
 113                         xm += 0x3 + ((xm >> 3) & 1);
 114                         /* xm += (xm&0x8)?0x4:0x3 */
 115                         break;
 116                 case IEEE754_RU:        /* toward +Infinity */
 117                         if (!sn)        /* ?? */
 118                                 xm += 0x8;
 119                         break;
 120                 case IEEE754_RD:        /* toward -Infinity */
 121                         if (sn) /* ?? */
 122                                 xm += 0x8;
 123                         break;
 124                 }
 125         }
 126         return xm;
 127 }
 128
 129
 130 /* generate a normal/denormal number with over,under handling
 131  * sn is sign
 132  * xe is an unbiased exponent
 133  * xm is 3bit extended precision value.
 134  */
 135 ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 136 {
 137         assert(xm);             /* we don't gen exact zeros (probably should) */
 138
 139         assert((xm >> (SP_MBITS + 1 + 3)) == 0);        /* no execess */
 140         assert(xm & (SP_HIDDEN_BIT << 3));
 141
 142         if (xe < SP_EMIN) {
 143                 /* strip lower bits */
 144                 int es = SP_EMIN - xe;
 145
 146                 if (ieee754_csr.nod) {
 147                         SETCX(IEEE754_UNDERFLOW);
 148                         SETCX(IEEE754_INEXACT);
 149
 150                         switch(ieee754_csr.rm) {
 151                         case IEEE754_RN:
 152                                 return ieee754sp_zero(sn);
 153                         case IEEE754_RZ:
 154                                 return ieee754sp_zero(sn);
 155                         case IEEE754_RU:      /* toward +Infinity */
 156                                 if(sn == 0)
 157                                         return ieee754sp_min(0);
 158                                 else
 159                                         return ieee754sp_zero(1);
 160                         case IEEE754_RD:      /* toward -Infinity */
 161                                 if(sn == 0)
 162                                         return ieee754sp_zero(0);
 163                                 else
 164                                         return ieee754sp_min(1);
 165                         }
 166                 }
 167
 168                 if (xe == SP_EMIN - 1
 169                                 && get_rounding(sn, xm) >> (SP_MBITS + 1 + 3))
 170                 {
 171                         /* Not tiny after rounding */
 172                         SETCX(IEEE754_INEXACT);
 173                         xm = get_rounding(sn, xm);
 174                         xm >>= 1;
 175                         /* Clear grs bits */
 176                         xm &= ~(SP_MBIT(3) - 1);
 177                         xe++;
 178                 }
 179                 else {
 180                         /* sticky right shift es bits
 181                          */
 182                         SPXSRSXn(es);
 183                         assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
 184                         assert(xe == SP_EMIN);
 185                 }
 186         }
 187         if (xm & (SP_MBIT(3) - 1)) {
 188                 SETCX(IEEE754_INEXACT);
 189                 if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
 190                         SETCX(IEEE754_UNDERFLOW);
 191                 }
 192
 193                 /* inexact must round of 3 bits
 194                  */
 195                 xm = get_rounding(sn, xm);
 196                 /* adjust exponent for rounding add overflowing
 197                  */
 198                 if (xm >> (SP_MBITS + 1 + 3)) {
 199                         /* add causes mantissa overflow */
 200                         xm >>= 1;
 201                         xe++;
 202                 }
 203         }
 204         /* strip grs bits */
 205         xm >>= 3;
 206
 207         assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 208         assert(xe >= SP_EMIN);
 209
 210         if (xe > SP_EMAX) {
 211                 SETCX(IEEE754_OVERFLOW);
 212                 SETCX(IEEE754_INEXACT);
 213                 /* -O can be table indexed by (rm,sn) */
 214                 switch (ieee754_csr.rm) {
 215                 case IEEE754_RN:
 216                         return ieee754sp_inf(sn);
 217                 case IEEE754_RZ:
 218                         return ieee754sp_max(sn);
 219                 case IEEE754_RU:        /* toward +Infinity */
 220                         if (sn == 0)
 221                                 return ieee754sp_inf(0);
 222                         else
 223                                 return ieee754sp_max(1);
 224                 case IEEE754_RD:        /* toward -Infinity */
 225                         if (sn == 0)
 226                                 return ieee754sp_max(0);
 227                         else
 228                                 return ieee754sp_inf(1);
 229                 }
 230         }
 231         /* gen norm/denorm/zero */
 232
 233         if ((xm & SP_HIDDEN_BIT) == 0) {
 234                 /* we underflow (tiny/zero) */
 235                 assert(xe == SP_EMIN);
 236                 if (ieee754_csr.mx & IEEE754_UNDERFLOW)
 237                         SETCX(IEEE754_UNDERFLOW);
 238                 return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
 239         } else {
 240                 assert((xm >> (SP_MBITS + 1)) == 0);    /* no execess */
 241                 assert(xm & SP_HIDDEN_BIT);
 242
 243                 return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
 244         }
 245 }