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 #include <stdarg.h>
  27 #include <linux/compiler.h>
  28
  29 #include "ieee754sp.h"
  30
  31 int ieee754sp_class(union ieee754sp x)
  32 {
  33         COMPXSP;
  34         EXPLODEXSP;
  35         return xc;
  36 }
  37
  38 int ieee754sp_isnan(union ieee754sp x)
  39 {
  40         return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
  41 }
  42
  43 int ieee754sp_issnan(union ieee754sp x)
  44 {
  45         assert(ieee754sp_isnan(x));
  46         return (SPMANT(x) & SP_MBIT(SP_FBITS-1));
  47 }
  48
  49
  50 union ieee754sp __cold ieee754sp_xcpt(union ieee754sp r, const char *op, ...)
  51 {
  52         struct ieee754xctx ax;
  53
  54         if (!ieee754_tstx())
  55                 return r;
  56
  57         ax.op = op;
  58         ax.rt = IEEE754_RT_SP;
  59         ax.rv.sp = r;
  60         va_start(ax.ap, op);
  61         ieee754_xcpt(&ax);
  62         va_end(ax.ap);
  63         return ax.rv.sp;
  64 }
  65
  66 union ieee754sp __cold ieee754sp_nanxcpt(union ieee754sp r, const char *op, ...)
  67 {
  68         struct ieee754xctx ax;
  69
  70         assert(ieee754sp_isnan(r));
  71
  72         if (!ieee754sp_issnan(r))       /* QNAN does not cause invalid op !! */
  73                 return r;
  74
  75         if (!ieee754_setandtestcx(IEEE754_INVALID_OPERATION)) {
  76                 /* not enabled convert to a quiet NaN */
  77                 SPMANT(r) &= (~SP_MBIT(SP_FBITS-1));
  78                 if (ieee754sp_isnan(r))
  79                         return r;
  80                 else
  81                         return ieee754sp_indef();
  82         }
  83
  84         ax.op = op;
  85         ax.rt = 0;
  86         ax.rv.sp = r;
  87         va_start(ax.ap, op);
  88         ieee754_xcpt(&ax);
  89         va_end(ax.ap);
  90         return ax.rv.sp;
  91 }
  92
  93 static unsigned get_rounding(int sn, unsigned xm)
  94 {
  95         /* inexact must round of 3 bits
  96          */
  97         if (xm & (SP_MBIT(3) - 1)) {
  98                 switch (ieee754_csr.rm) {
  99                 case IEEE754_RZ:
 100                         break;
 101                 case IEEE754_RN:
 102                         xm += 0x3 + ((xm >> 3) & 1);
 103                         /* xm += (xm&0x8)?0x4:0x3 */
 104                         break;
 105                 case IEEE754_RU:        /* toward +Infinity */
 106                         if (!sn)        /* ?? */
 107                                 xm += 0x8;
 108                         break;
 109                 case IEEE754_RD:        /* toward -Infinity */
 110                         if (sn) /* ?? */
 111                                 xm += 0x8;
 112                         break;
 113                 }
 114         }
 115         return xm;
 116 }
 117
 118
 119 /* generate a normal/denormal number with over,under handling
 120  * sn is sign
 121  * xe is an unbiased exponent
 122  * xm is 3bit extended precision value.
 123  */
 124 union ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
 125 {
 126         assert(xm);             /* we don't gen exact zeros (probably should) */
 127
 128         assert((xm >> (SP_FBITS + 1 + 3)) == 0);        /* no execess */
 129         assert(xm & (SP_HIDDEN_BIT << 3));
 130
 131         if (xe < SP_EMIN) {
 132                 /* strip lower bits */
 133                 int es = SP_EMIN - xe;
 134
 135                 if (ieee754_csr.nod) {
 136                         ieee754_setcx(IEEE754_UNDERFLOW);
 137                         ieee754_setcx(IEEE754_INEXACT);
 138
 139                         switch(ieee754_csr.rm) {
 140                         case IEEE754_RN:
 141                         case IEEE754_RZ:
 142                                 return ieee754sp_zero(sn);
 143                         case IEEE754_RU:      /* toward +Infinity */
 144                                 if (sn == 0)
 145                                         return ieee754sp_min(0);
 146                                 else
 147                                         return ieee754sp_zero(1);
 148                         case IEEE754_RD:      /* toward -Infinity */
 149                                 if (sn == 0)
 150                                         return ieee754sp_zero(0);
 151                                 else
 152                                         return ieee754sp_min(1);
 153                         }
 154                 }
 155
 156                 if (xe == SP_EMIN - 1
 157                                 && get_rounding(sn, xm) >> (SP_FBITS + 1 + 3))
 158                 {
 159                         /* Not tiny after rounding */
 160                         ieee754_setcx(IEEE754_INEXACT);
 161                         xm = get_rounding(sn, xm);
 162                         xm >>= 1;
 163                         /* Clear grs bits */
 164                         xm &= ~(SP_MBIT(3) - 1);
 165                         xe++;
 166                 } else {
 167                         /* sticky right shift es bits
 168                          */
 169                         SPXSRSXn(es);
 170                         assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
 171                         assert(xe == SP_EMIN);
 172                 }
 173         }
 174         if (xm & (SP_MBIT(3) - 1)) {
 175                 ieee754_setcx(IEEE754_INEXACT);
 176                 if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
 177                         ieee754_setcx(IEEE754_UNDERFLOW);
 178                 }
 179
 180                 /* inexact must round of 3 bits
 181                  */
 182                 xm = get_rounding(sn, xm);
 183                 /* adjust exponent for rounding add overflowing
 184                  */
 185                 if (xm >> (SP_FBITS + 1 + 3)) {
 186                         /* add causes mantissa overflow */
 187                         xm >>= 1;
 188                         xe++;
 189                 }
 190         }
 191         /* strip grs bits */
 192         xm >>= 3;
 193
 194         assert((xm >> (SP_FBITS + 1)) == 0);    /* no execess */
 195         assert(xe >= SP_EMIN);
 196
 197         if (xe > SP_EMAX) {
 198                 ieee754_setcx(IEEE754_OVERFLOW);
 199                 ieee754_setcx(IEEE754_INEXACT);
 200                 /* -O can be table indexed by (rm,sn) */
 201                 switch (ieee754_csr.rm) {
 202                 case IEEE754_RN:
 203                         return ieee754sp_inf(sn);
 204                 case IEEE754_RZ:
 205                         return ieee754sp_max(sn);
 206                 case IEEE754_RU:        /* toward +Infinity */
 207                         if (sn == 0)
 208                                 return ieee754sp_inf(0);
 209                         else
 210                                 return ieee754sp_max(1);
 211                 case IEEE754_RD:        /* toward -Infinity */
 212                         if (sn == 0)
 213                                 return ieee754sp_max(0);
 214                         else
 215                                 return ieee754sp_inf(1);
 216                 }
 217         }
 218         /* gen norm/denorm/zero */
 219
 220         if ((xm & SP_HIDDEN_BIT) == 0) {
 221                 /* we underflow (tiny/zero) */
 222                 assert(xe == SP_EMIN);
 223                 if (ieee754_csr.mx & IEEE754_UNDERFLOW)
 224                         ieee754_setcx(IEEE754_UNDERFLOW);
 225                 return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
 226         } else {
 227                 assert((xm >> (SP_FBITS + 1)) == 0);    /* no execess */
 228                 assert(xm & SP_HIDDEN_BIT);
 229
 230                 return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
 231         }
 232 }