arch/i386/math-emu/reg_add_sub.c

   1 /*---------------------------------------------------------------------------+
   2  |  reg_add_sub.c                                                            |
   3  |                                                                           |
   4  | Functions to add or subtract two registers and put the result in a third. |
   5  |                                                                           |
   6  | Copyright (C) 1992,1993,1997                                              |
   7  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   8  |                  E-mail   billm@suburbia.net                              |
   9  |                                                                           |
  10  |                                                                           |
  11  +---------------------------------------------------------------------------*/
  12
  13 /*---------------------------------------------------------------------------+
  14  |  For each function, the destination may be any FPU_REG, including one of  |
  15  | the source FPU_REGs.                                                      |
  16  |  Each function returns 0 if the answer is o.k., otherwise a non-zero      |
  17  | value is returned, indicating either an exception condition or an         |
  18  | internal error.                                                           |
  19  +---------------------------------------------------------------------------*/
  20
  21 #include "exception.h"
  22 #include "reg_constant.h"
  23 #include "fpu_emu.h"
  24 #include "control_w.h"
  25 #include "fpu_system.h"
  26
  27 static
  28 int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
  29                      FPU_REG const *b, u_char tagb, u_char signb,
  30                      FPU_REG *dest, int deststnr, int control_w);
  31
  32 /*
  33   Operates on st(0) and st(n), or on st(0) and temporary data.
  34   The destination must be one of the source st(x).
  35   */
  36 int FPU_add(FPU_REG const *b, u_char tagb, int deststnr, int control_w)
  37 {
  38   FPU_REG *a = &st(0);
  39   FPU_REG *dest = &st(deststnr);
  40   u_char signb = getsign(b);
  41   u_char taga = FPU_gettag0();
  42   u_char signa = getsign(a);
  43   u_char saved_sign = getsign(dest);
  44   int diff, tag, expa, expb;
  45
  46   if ( !(taga | tagb) )
  47     {
  48       expa = exponent(a);
  49       expb = exponent(b);
  50
  51     valid_add:
  52       /* Both registers are valid */
  53       if (!(signa ^ signb))
  54         {
  55           /* signs are the same */
  56           tag = FPU_u_add(a, b, dest, control_w, signa, expa, expb);
  57         }
  58       else
  59         {
  60           /* The signs are different, so do a subtraction */
  61           diff = expa - expb;
  62           if (!diff)
  63             {
  64               diff = a->sigh - b->sigh;  /* This works only if the ms bits
  65                                             are identical. */
  66               if (!diff)
  67                 {
  68                   diff = a->sigl > b->sigl;
  69                   if (!diff)
  70                     diff = -(a->sigl < b->sigl);
  71                 }
  72             }
  73
  74           if (diff > 0)
  75             {
  76               tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
  77             }
  78           else if ( diff < 0 )
  79             {
  80               tag = FPU_u_sub(b, a, dest, control_w, signb, expb, expa);
  81             }
  82           else
  83             {
  84               FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
  85               /* sign depends upon rounding mode */
  86               setsign(dest, ((control_w & CW_RC) != RC_DOWN)
  87                       ? SIGN_POS : SIGN_NEG);
  88               return TAG_Zero;
  89             }
  90         }
  91
  92       if ( tag < 0 )
  93         {
  94           setsign(dest, saved_sign);
  95           return tag;
  96         }
  97       FPU_settagi(deststnr, tag);
  98       return tag;
  99     }
 100
 101   if ( taga == TAG_Special )
 102     taga = FPU_Special(a);
 103   if ( tagb == TAG_Special )
 104     tagb = FPU_Special(b);
 105
 106   if ( ((taga == TAG_Valid) && (tagb == TW_Denormal))
 107             || ((taga == TW_Denormal) && (tagb == TAG_Valid))
 108             || ((taga == TW_Denormal) && (tagb == TW_Denormal)) )
 109     {
 110       FPU_REG x, y;
 111
 112       if ( denormal_operand() < 0 )
 113         return FPU_Exception;
 114
 115       FPU_to_exp16(a, &x);
 116       FPU_to_exp16(b, &y);
 117       a = &x;
 118       b = &y;
 119       expa = exponent16(a);
 120       expb = exponent16(b);
 121       goto valid_add;
 122     }
 123
 124   if ( (taga == TW_NaN) || (tagb == TW_NaN) )
 125     {
 126       if ( deststnr == 0 )
 127         return real_2op_NaN(b, tagb, deststnr, a);
 128       else
 129         return real_2op_NaN(a, taga, deststnr, a);
 130     }
 131
 132   return add_sub_specials(a, taga, signa, b, tagb, signb,
 133                           dest, deststnr, control_w);
 134 }
 135
 136
 137 /* Subtract b from a.  (a-b) -> dest */
 138 int FPU_sub(int flags, int rm, int control_w)
 139 {
 140   FPU_REG const *a, *b;
 141   FPU_REG *dest;
 142   u_char taga, tagb, signa, signb, saved_sign, sign;
 143   int diff, tag = 0, expa, expb, deststnr;
 144
 145   a = &st(0);
 146   taga = FPU_gettag0();
 147
 148   deststnr = 0;
 149   if ( flags & LOADED )
 150     {
 151       b = (FPU_REG *)rm;
 152       tagb = flags & 0x0f;
 153     }
 154   else
 155     {
 156       b = &st(rm);
 157       tagb = FPU_gettagi(rm);
 158
 159       if ( flags & DEST_RM )
 160         deststnr = rm;
 161     }
 162
 163   signa = getsign(a);
 164   signb = getsign(b);
 165
 166   if ( flags & REV )
 167     {
 168       signa ^= SIGN_NEG;
 169       signb ^= SIGN_NEG;
 170     }
 171
 172   dest = &st(deststnr);
 173   saved_sign = getsign(dest);
 174
 175   if ( !(taga | tagb) )
 176     {
 177       expa = exponent(a);
 178       expb = exponent(b);
 179
 180     valid_subtract:
 181       /* Both registers are valid */
 182
 183       diff = expa - expb;
 184
 185       if (!diff)
 186         {
 187           diff = a->sigh - b->sigh;  /* Works only if ms bits are identical */
 188           if (!diff)
 189             {
 190               diff = a->sigl > b->sigl;
 191               if (!diff)
 192                 diff = -(a->sigl < b->sigl);
 193             }
 194         }
 195
 196       switch ( (((int)signa)*2 + signb) / SIGN_NEG )
 197         {
 198         case 0: /* P - P */
 199         case 3: /* N - N */
 200           if (diff > 0)
 201             {
 202               /* |a| > |b| */
 203               tag = FPU_u_sub(a, b, dest, control_w, signa, expa, expb);
 204             }
 205           else if ( diff == 0 )
 206             {
 207               FPU_copy_to_regi(&CONST_Z, TAG_Zero, deststnr);
 208
 209               /* sign depends upon rounding mode */
 210               setsign(dest, ((control_w & CW_RC) != RC_DOWN)
 211                 ? SIGN_POS : SIGN_NEG);
 212               return TAG_Zero;
 213             }
 214           else
 215             {
 216               sign = signa ^ SIGN_NEG;
 217               tag = FPU_u_sub(b, a, dest, control_w, sign, expb, expa);
 218             }
 219           break;
 220         case 1: /* P - N */
 221           tag = FPU_u_add(a, b, dest, control_w, SIGN_POS, expa, expb);
 222           break;
 223         case 2: /* N - P */
 224           tag = FPU_u_add(a, b, dest, control_w, SIGN_NEG, expa, expb);
 225           break;
 226 #ifdef PARANOID
 227         default:
 228           EXCEPTION(EX_INTERNAL|0x111);
 229           return -1;
 230 #endif
 231         }
 232       if ( tag < 0 )
 233         {
 234           setsign(dest, saved_sign);
 235           return tag;
 236         }
 237       FPU_settagi(deststnr, tag);
 238       return tag;
 239     }
 240
 241   if ( taga == TAG_Special )
 242     taga = FPU_Special(a);
 243   if ( tagb == TAG_Special )
 244     tagb = FPU_Special(b);
 245
 246   if ( ((taga == TAG_Valid) && (tagb == TW_Denormal))
 247             || ((taga == TW_Denormal) && (tagb == TAG_Valid))
 248             || ((taga == TW_Denormal) && (tagb == TW_Denormal)) )
 249     {
 250       FPU_REG x, y;
 251
 252       if ( denormal_operand() < 0 )
 253         return FPU_Exception;
 254
 255       FPU_to_exp16(a, &x);
 256       FPU_to_exp16(b, &y);
 257       a = &x;
 258       b = &y;
 259       expa = exponent16(a);
 260       expb = exponent16(b);
 261
 262       goto valid_subtract;
 263     }
 264
 265   if ( (taga == TW_NaN) || (tagb == TW_NaN) )
 266     {
 267       FPU_REG const *d1, *d2;
 268       if ( flags & REV )
 269         {
 270           d1 = b;
 271           d2 = a;
 272         }
 273       else
 274         {
 275           d1 = a;
 276           d2 = b;
 277         }
 278       if ( flags & LOADED )
 279         return real_2op_NaN(b, tagb, deststnr, d1);
 280       if ( flags & DEST_RM )
 281         return real_2op_NaN(a, taga, deststnr, d2);
 282       else
 283         return real_2op_NaN(b, tagb, deststnr, d2);
 284     }
 285
 286     return add_sub_specials(a, taga, signa, b, tagb, signb ^ SIGN_NEG,
 287                             dest, deststnr, control_w);
 288 }
 289
 290
 291 static
 292 int add_sub_specials(FPU_REG const *a, u_char taga, u_char signa,
 293                      FPU_REG const *b, u_char tagb, u_char signb,
 294                      FPU_REG *dest, int deststnr, int control_w)
 295 {
 296   if ( ((taga == TW_Denormal) || (tagb == TW_Denormal))
 297        && (denormal_operand() < 0) )
 298     return FPU_Exception;
 299
 300   if (taga == TAG_Zero)
 301     {
 302       if (tagb == TAG_Zero)
 303         {
 304           /* Both are zero, result will be zero. */
 305           u_char different_signs = signa ^ signb;
 306
 307           FPU_copy_to_regi(a, TAG_Zero, deststnr);
 308           if ( different_signs )
 309             {
 310               /* Signs are different. */
 311               /* Sign of answer depends upon rounding mode. */
 312               setsign(dest, ((control_w & CW_RC) != RC_DOWN)
 313                       ? SIGN_POS : SIGN_NEG);
 314             }
 315           else
 316             setsign(dest, signa);  /* signa may differ from the sign of a. */
 317           return TAG_Zero;
 318         }
 319       else
 320         {
 321           reg_copy(b, dest);
 322           if ( (tagb == TW_Denormal) && (b->sigh & 0x80000000) )
 323             {
 324               /* A pseudoDenormal, convert it. */
 325               addexponent(dest, 1);
 326               tagb = TAG_Valid;
 327             }
 328           else if ( tagb > TAG_Empty )
 329             tagb = TAG_Special;
 330           setsign(dest, signb);  /* signb may differ from the sign of b. */
 331           FPU_settagi(deststnr, tagb);
 332           return tagb;
 333         }
 334     }
 335   else if (tagb == TAG_Zero)
 336     {
 337       reg_copy(a, dest);
 338       if ( (taga == TW_Denormal) && (a->sigh & 0x80000000) )
 339         {
 340           /* A pseudoDenormal */
 341           addexponent(dest, 1);
 342           taga = TAG_Valid;
 343         }
 344       else if ( taga > TAG_Empty )
 345         taga = TAG_Special;
 346       setsign(dest, signa);  /* signa may differ from the sign of a. */
 347       FPU_settagi(deststnr, taga);
 348       return taga;
 349     }
 350   else if (taga == TW_Infinity)
 351     {
 352       if ( (tagb != TW_Infinity) || (signa == signb) )
 353         {
 354           FPU_copy_to_regi(a, TAG_Special, deststnr);
 355           setsign(dest, signa);  /* signa may differ from the sign of a. */
 356           return taga;
 357         }
 358       /* Infinity-Infinity is undefined. */
 359       return arith_invalid(deststnr);
 360     }
 361   else if (tagb == TW_Infinity)
 362     {
 363       FPU_copy_to_regi(b, TAG_Special, deststnr);
 364       setsign(dest, signb);  /* signb may differ from the sign of b. */
 365       return tagb;
 366     }
 367
 368 #ifdef PARANOID
 369   EXCEPTION(EX_INTERNAL|0x101);
 370 #endif
 371
 372   return FPU_Exception;
 373 }
 374