arch/x86/math-emu/errors.c

   1 /*---------------------------------------------------------------------------+
   2  |  errors.c                                                                 |
   3  |                                                                           |
   4  |  The error handling functions for wm-FPU-emu                              |
   5  |                                                                           |
   6  | Copyright (C) 1992,1993,1994,1996                                         |
   7  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   8  |                  E-mail   billm@jacobi.maths.monash.edu.au                |
   9  |                                                                           |
  10  |                                                                           |
  11  +---------------------------------------------------------------------------*/
  12
  13 /*---------------------------------------------------------------------------+
  14  | Note:                                                                     |
  15  |    The file contains code which accesses user memory.                     |
  16  |    Emulator static data may change when user memory is accessed, due to   |
  17  |    other processes using the emulator while swapping is in progress.      |
  18  +---------------------------------------------------------------------------*/
  19
  20 #include <linux/signal.h>
  21
  22 #include <asm/uaccess.h>
  23
  24 #include "fpu_emu.h"
  25 #include "fpu_system.h"
  26 #include "exception.h"
  27 #include "status_w.h"
  28 #include "control_w.h"
  29 #include "reg_constant.h"
  30 #include "version.h"
  31
  32 /* */
  33 #undef PRINT_MESSAGES
  34 /* */
  35
  36 #if 0
  37 void Un_impl(void)
  38 {
  39         u_char byte1, FPU_modrm;
  40         unsigned long address = FPU_ORIG_EIP;
  41
  42         RE_ENTRANT_CHECK_OFF;
  43         /* No need to check access_ok(), we have previously fetched these bytes. */
  44         printk("Unimplemented FPU Opcode at eip=%p : ", (void __user *)address);
  45         if (FPU_CS == __USER_CS) {
  46                 while (1) {
  47                         FPU_get_user(byte1, (u_char __user *) address);
  48                         if ((byte1 & 0xf8) == 0xd8)
  49                                 break;
  50                         printk("[%02x]", byte1);
  51                         address++;
  52                 }
  53                 printk("%02x ", byte1);
  54                 FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
  55
  56                 if (FPU_modrm >= 0300)
  57                         printk("%02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8,
  58                                FPU_modrm & 7);
  59                 else
  60                         printk("/%d\n", (FPU_modrm >> 3) & 7);
  61         } else {
  62                 printk("cs selector = %04x\n", FPU_CS);
  63         }
  64
  65         RE_ENTRANT_CHECK_ON;
  66
  67         EXCEPTION(EX_Invalid);
  68
  69 }
  70 #endif /*  0  */
  71
  72 /*
  73    Called for opcodes which are illegal and which are known to result in a
  74    SIGILL with a real 80486.
  75    */
  76 void FPU_illegal(void)
  77 {
  78         math_abort(FPU_info, SIGILL);
  79 }
  80
  81 void FPU_printall(void)
  82 {
  83         int i;
  84         static const char *tag_desc[] = { "Valid", "Zero", "ERROR", "Empty",
  85                 "DeNorm", "Inf", "NaN"
  86         };
  87         u_char byte1, FPU_modrm;
  88         unsigned long address = FPU_ORIG_EIP;
  89
  90         RE_ENTRANT_CHECK_OFF;
  91         /* No need to check access_ok(), we have previously fetched these bytes. */
  92         printk("At %p:", (void *)address);
  93         if (FPU_CS == __USER_CS) {
  94 #define MAX_PRINTED_BYTES 20
  95                 for (i = 0; i < MAX_PRINTED_BYTES; i++) {
  96                         FPU_get_user(byte1, (u_char __user *) address);
  97                         if ((byte1 & 0xf8) == 0xd8) {
  98                                 printk(" %02x", byte1);
  99                                 break;
 100                         }
 101                         printk(" [%02x]", byte1);
 102                         address++;
 103                 }
 104                 if (i == MAX_PRINTED_BYTES)
 105                         printk(" [more..]\n");
 106                 else {
 107                         FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
 108
 109                         if (FPU_modrm >= 0300)
 110                                 printk(" %02x (%02x+%d)\n", FPU_modrm,
 111                                        FPU_modrm & 0xf8, FPU_modrm & 7);
 112                         else
 113                                 printk(" /%d, mod=%d rm=%d\n",
 114                                        (FPU_modrm >> 3) & 7,
 115                                        (FPU_modrm >> 6) & 3, FPU_modrm & 7);
 116                 }
 117         } else {
 118                 printk("%04x\n", FPU_CS);
 119         }
 120
 121         partial_status = status_word();
 122
 123 #ifdef DEBUGGING
 124         if (partial_status & SW_Backward)
 125                 printk("SW: backward compatibility\n");
 126         if (partial_status & SW_C3)
 127                 printk("SW: condition bit 3\n");
 128         if (partial_status & SW_C2)
 129                 printk("SW: condition bit 2\n");
 130         if (partial_status & SW_C1)
 131                 printk("SW: condition bit 1\n");
 132         if (partial_status & SW_C0)
 133                 printk("SW: condition bit 0\n");
 134         if (partial_status & SW_Summary)
 135                 printk("SW: exception summary\n");
 136         if (partial_status & SW_Stack_Fault)
 137                 printk("SW: stack fault\n");
 138         if (partial_status & SW_Precision)
 139                 printk("SW: loss of precision\n");
 140         if (partial_status & SW_Underflow)
 141                 printk("SW: underflow\n");
 142         if (partial_status & SW_Overflow)
 143                 printk("SW: overflow\n");
 144         if (partial_status & SW_Zero_Div)
 145                 printk("SW: divide by zero\n");
 146         if (partial_status & SW_Denorm_Op)
 147                 printk("SW: denormalized operand\n");
 148         if (partial_status & SW_Invalid)
 149                 printk("SW: invalid operation\n");
 150 #endif /* DEBUGGING */
 151
 152         printk(" SW: b=%d st=%d es=%d sf=%d cc=%d%d%d%d ef=%d%d%d%d%d%d\n", partial_status & 0x8000 ? 1 : 0,    /* busy */
 153                (partial_status & 0x3800) >> 11, /* stack top pointer */
 154                partial_status & 0x80 ? 1 : 0,   /* Error summary status */
 155                partial_status & 0x40 ? 1 : 0,   /* Stack flag */
 156                partial_status & SW_C3 ? 1 : 0, partial_status & SW_C2 ? 1 : 0,  /* cc */
 157                partial_status & SW_C1 ? 1 : 0, partial_status & SW_C0 ? 1 : 0,  /* cc */
 158                partial_status & SW_Precision ? 1 : 0,
 159                partial_status & SW_Underflow ? 1 : 0,
 160                partial_status & SW_Overflow ? 1 : 0,
 161                partial_status & SW_Zero_Div ? 1 : 0,
 162                partial_status & SW_Denorm_Op ? 1 : 0,
 163                partial_status & SW_Invalid ? 1 : 0);
 164
 165         printk(" CW: ic=%d rc=%d%d pc=%d%d iem=%d     ef=%d%d%d%d%d%d\n",
 166                control_word & 0x1000 ? 1 : 0,
 167                (control_word & 0x800) >> 11, (control_word & 0x400) >> 10,
 168                (control_word & 0x200) >> 9, (control_word & 0x100) >> 8,
 169                control_word & 0x80 ? 1 : 0,
 170                control_word & SW_Precision ? 1 : 0,
 171                control_word & SW_Underflow ? 1 : 0,
 172                control_word & SW_Overflow ? 1 : 0,
 173                control_word & SW_Zero_Div ? 1 : 0,
 174                control_word & SW_Denorm_Op ? 1 : 0,
 175                control_word & SW_Invalid ? 1 : 0);
 176
 177         for (i = 0; i < 8; i++) {
 178                 FPU_REG *r = &st(i);
 179                 u_char tagi = FPU_gettagi(i);
 180                 switch (tagi) {
 181                 case TAG_Empty:
 182                         continue;
 183                         break;
 184                 case TAG_Zero:
 185                 case TAG_Special:
 186                         tagi = FPU_Special(r);
 187                 case TAG_Valid:
 188                         printk("st(%d)  %c .%04lx %04lx %04lx %04lx e%+-6d ", i,
 189                                getsign(r) ? '-' : '+',
 190                                (long)(r->sigh >> 16),
 191                                (long)(r->sigh & 0xFFFF),
 192                                (long)(r->sigl >> 16),
 193                                (long)(r->sigl & 0xFFFF),
 194                                exponent(r) - EXP_BIAS + 1);
 195                         break;
 196                 default:
 197                         printk("Whoops! Error in errors.c: tag%d is %d ", i,
 198                                tagi);
 199                         continue;
 200                         break;
 201                 }
 202                 printk("%s\n", tag_desc[(int)(unsigned)tagi]);
 203         }
 204
 205         RE_ENTRANT_CHECK_ON;
 206
 207 }
 208
 209 static struct {
 210         int type;
 211         const char *name;
 212 } exception_names[] = {
 213         {
 214         EX_StackOver, "stack overflow"}, {
 215         EX_StackUnder, "stack underflow"}, {
 216         EX_Precision, "loss of precision"}, {
 217         EX_Underflow, "underflow"}, {
 218         EX_Overflow, "overflow"}, {
 219         EX_ZeroDiv, "divide by zero"}, {
 220         EX_Denormal, "denormalized operand"}, {
 221         EX_Invalid, "invalid operation"}, {
 222         EX_INTERNAL, "INTERNAL BUG in " FPU_VERSION}, {
 223         0, NULL}
 224 };
 225
 226 /*
 227  EX_INTERNAL is always given with a code which indicates where the
 228  error was detected.
 229
 230  Internal error types:
 231        0x14   in fpu_etc.c
 232        0x1nn  in a *.c file:
 233               0x101  in reg_add_sub.c
 234               0x102  in reg_mul.c
 235               0x104  in poly_atan.c
 236               0x105  in reg_mul.c
 237               0x107  in fpu_trig.c
 238               0x108  in reg_compare.c
 239               0x109  in reg_compare.c
 240               0x110  in reg_add_sub.c
 241               0x111  in fpe_entry.c
 242               0x112  in fpu_trig.c
 243               0x113  in errors.c
 244               0x115  in fpu_trig.c
 245               0x116  in fpu_trig.c
 246               0x117  in fpu_trig.c
 247               0x118  in fpu_trig.c
 248               0x119  in fpu_trig.c
 249               0x120  in poly_atan.c
 250               0x121  in reg_compare.c
 251               0x122  in reg_compare.c
 252               0x123  in reg_compare.c
 253               0x125  in fpu_trig.c
 254               0x126  in fpu_entry.c
 255               0x127  in poly_2xm1.c
 256               0x128  in fpu_entry.c
 257               0x129  in fpu_entry.c
 258               0x130  in get_address.c
 259               0x131  in get_address.c
 260               0x132  in get_address.c
 261               0x133  in get_address.c
 262               0x140  in load_store.c
 263               0x141  in load_store.c
 264               0x150  in poly_sin.c
 265               0x151  in poly_sin.c
 266               0x160  in reg_ld_str.c
 267               0x161  in reg_ld_str.c
 268               0x162  in reg_ld_str.c
 269               0x163  in reg_ld_str.c
 270               0x164  in reg_ld_str.c
 271               0x170  in fpu_tags.c
 272               0x171  in fpu_tags.c
 273               0x172  in fpu_tags.c
 274               0x180  in reg_convert.c
 275        0x2nn  in an *.S file:
 276               0x201  in reg_u_add.S
 277               0x202  in reg_u_div.S
 278               0x203  in reg_u_div.S
 279               0x204  in reg_u_div.S
 280               0x205  in reg_u_mul.S
 281               0x206  in reg_u_sub.S
 282               0x207  in wm_sqrt.S
 283               0x208  in reg_div.S
 284               0x209  in reg_u_sub.S
 285               0x210  in reg_u_sub.S
 286               0x211  in reg_u_sub.S
 287               0x212  in reg_u_sub.S
 288               0x213  in wm_sqrt.S
 289               0x214  in wm_sqrt.S
 290               0x215  in wm_sqrt.S
 291               0x220  in reg_norm.S
 292               0x221  in reg_norm.S
 293               0x230  in reg_round.S
 294               0x231  in reg_round.S
 295               0x232  in reg_round.S
 296               0x233  in reg_round.S
 297               0x234  in reg_round.S
 298               0x235  in reg_round.S
 299               0x236  in reg_round.S
 300               0x240  in div_Xsig.S
 301               0x241  in div_Xsig.S
 302               0x242  in div_Xsig.S
 303  */
 304
 305 asmlinkage __visible void FPU_exception(int n)
 306 {
 307         int i, int_type;
 308
 309         int_type = 0;           /* Needed only to stop compiler warnings */
 310         if (n & EX_INTERNAL) {
 311                 int_type = n - EX_INTERNAL;
 312                 n = EX_INTERNAL;
 313                 /* Set lots of exception bits! */
 314                 partial_status |= (SW_Exc_Mask | SW_Summary | SW_Backward);
 315         } else {
 316                 /* Extract only the bits which we use to set the status word */
 317                 n &= (SW_Exc_Mask);
 318                 /* Set the corresponding exception bit */
 319                 partial_status |= n;
 320                 /* Set summary bits iff exception isn't masked */
 321                 if (partial_status & ~control_word & CW_Exceptions)
 322                         partial_status |= (SW_Summary | SW_Backward);
 323                 if (n & (SW_Stack_Fault | EX_Precision)) {
 324                         if (!(n & SW_C1))
 325                                 /* This bit distinguishes over- from underflow for a stack fault,
 326                                    and roundup from round-down for precision loss. */
 327                                 partial_status &= ~SW_C1;
 328                 }
 329         }
 330
 331         RE_ENTRANT_CHECK_OFF;
 332         if ((~control_word & n & CW_Exceptions) || (n == EX_INTERNAL)) {
 333                 /* Get a name string for error reporting */
 334                 for (i = 0; exception_names[i].type; i++)
 335                         if ((exception_names[i].type & n) ==
 336                             exception_names[i].type)
 337                                 break;
 338
 339                 if (exception_names[i].type) {
 340 #ifdef PRINT_MESSAGES
 341                         printk("FP Exception: %s!\n", exception_names[i].name);
 342 #endif /* PRINT_MESSAGES */
 343                 } else
 344                         printk("FPU emulator: Unknown Exception: 0x%04x!\n", n);
 345
 346                 if (n == EX_INTERNAL) {
 347                         printk("FPU emulator: Internal error type 0x%04x\n",
 348                                int_type);
 349                         FPU_printall();
 350                 }
 351 #ifdef PRINT_MESSAGES
 352                 else
 353                         FPU_printall();
 354 #endif /* PRINT_MESSAGES */
 355
 356                 /*
 357                  * The 80486 generates an interrupt on the next non-control FPU
 358                  * instruction. So we need some means of flagging it.
 359                  * We use the ES (Error Summary) bit for this.
 360                  */
 361         }
 362         RE_ENTRANT_CHECK_ON;
 363
 364 #ifdef __DEBUG__
 365         math_abort(FPU_info, SIGFPE);
 366 #endif /* __DEBUG__ */
 367
 368 }
 369
 370 /* Real operation attempted on a NaN. */
 371 /* Returns < 0 if the exception is unmasked */
 372 int real_1op_NaN(FPU_REG *a)
 373 {
 374         int signalling, isNaN;
 375
 376         isNaN = (exponent(a) == EXP_OVER) && (a->sigh & 0x80000000);
 377
 378         /* The default result for the case of two "equal" NaNs (signs may
 379            differ) is chosen to reproduce 80486 behaviour */
 380         signalling = isNaN && !(a->sigh & 0x40000000);
 381
 382         if (!signalling) {
 383                 if (!isNaN) {   /* pseudo-NaN, or other unsupported? */
 384                         if (control_word & CW_Invalid) {
 385                                 /* Masked response */
 386                                 reg_copy(&CONST_QNaN, a);
 387                         }
 388                         EXCEPTION(EX_Invalid);
 389                         return (!(control_word & CW_Invalid) ? FPU_Exception :
 390                                 0) | TAG_Special;
 391                 }
 392                 return TAG_Special;
 393         }
 394
 395         if (control_word & CW_Invalid) {
 396                 /* The masked response */
 397                 if (!(a->sigh & 0x80000000)) {  /* pseudo-NaN ? */
 398                         reg_copy(&CONST_QNaN, a);
 399                 }
 400                 /* ensure a Quiet NaN */
 401                 a->sigh |= 0x40000000;
 402         }
 403
 404         EXCEPTION(EX_Invalid);
 405
 406         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 407 }
 408
 409 /* Real operation attempted on two operands, one a NaN. */
 410 /* Returns < 0 if the exception is unmasked */
 411 int real_2op_NaN(FPU_REG const *b, u_char tagb,
 412                  int deststnr, FPU_REG const *defaultNaN)
 413 {
 414         FPU_REG *dest = &st(deststnr);
 415         FPU_REG const *a = dest;
 416         u_char taga = FPU_gettagi(deststnr);
 417         FPU_REG const *x;
 418         int signalling, unsupported;
 419
 420         if (taga == TAG_Special)
 421                 taga = FPU_Special(a);
 422         if (tagb == TAG_Special)
 423                 tagb = FPU_Special(b);
 424
 425         /* TW_NaN is also used for unsupported data types. */
 426         unsupported = ((taga == TW_NaN)
 427                        && !((exponent(a) == EXP_OVER)
 428                             && (a->sigh & 0x80000000)))
 429             || ((tagb == TW_NaN)
 430                 && !((exponent(b) == EXP_OVER) && (b->sigh & 0x80000000)));
 431         if (unsupported) {
 432                 if (control_word & CW_Invalid) {
 433                         /* Masked response */
 434                         FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 435                 }
 436                 EXCEPTION(EX_Invalid);
 437                 return (!(control_word & CW_Invalid) ? FPU_Exception : 0) |
 438                     TAG_Special;
 439         }
 440
 441         if (taga == TW_NaN) {
 442                 x = a;
 443                 if (tagb == TW_NaN) {
 444                         signalling = !(a->sigh & b->sigh & 0x40000000);
 445                         if (significand(b) > significand(a))
 446                                 x = b;
 447                         else if (significand(b) == significand(a)) {
 448                                 /* The default result for the case of two "equal" NaNs (signs may
 449                                    differ) is chosen to reproduce 80486 behaviour */
 450                                 x = defaultNaN;
 451                         }
 452                 } else {
 453                         /* return the quiet version of the NaN in a */
 454                         signalling = !(a->sigh & 0x40000000);
 455                 }
 456         } else
 457 #ifdef PARANOID
 458         if (tagb == TW_NaN)
 459 #endif /* PARANOID */
 460         {
 461                 signalling = !(b->sigh & 0x40000000);
 462                 x = b;
 463         }
 464 #ifdef PARANOID
 465         else {
 466                 signalling = 0;
 467                 EXCEPTION(EX_INTERNAL | 0x113);
 468                 x = &CONST_QNaN;
 469         }
 470 #endif /* PARANOID */
 471
 472         if ((!signalling) || (control_word & CW_Invalid)) {
 473                 if (!x)
 474                         x = b;
 475
 476                 if (!(x->sigh & 0x80000000))    /* pseudo-NaN ? */
 477                         x = &CONST_QNaN;
 478
 479                 FPU_copy_to_regi(x, TAG_Special, deststnr);
 480
 481                 if (!signalling)
 482                         return TAG_Special;
 483
 484                 /* ensure a Quiet NaN */
 485                 dest->sigh |= 0x40000000;
 486         }
 487
 488         EXCEPTION(EX_Invalid);
 489
 490         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 491 }
 492
 493 /* Invalid arith operation on Valid registers */
 494 /* Returns < 0 if the exception is unmasked */
 495 asmlinkage __visible int arith_invalid(int deststnr)
 496 {
 497
 498         EXCEPTION(EX_Invalid);
 499
 500         if (control_word & CW_Invalid) {
 501                 /* The masked response */
 502                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 503         }
 504
 505         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Valid;
 506
 507 }
 508
 509 /* Divide a finite number by zero */
 510 asmlinkage __visible int FPU_divide_by_zero(int deststnr, u_char sign)
 511 {
 512         FPU_REG *dest = &st(deststnr);
 513         int tag = TAG_Valid;
 514
 515         if (control_word & CW_ZeroDiv) {
 516                 /* The masked response */
 517                 FPU_copy_to_regi(&CONST_INF, TAG_Special, deststnr);
 518                 setsign(dest, sign);
 519                 tag = TAG_Special;
 520         }
 521
 522         EXCEPTION(EX_ZeroDiv);
 523
 524         return (!(control_word & CW_ZeroDiv) ? FPU_Exception : 0) | tag;
 525
 526 }
 527
 528 /* This may be called often, so keep it lean */
 529 int set_precision_flag(int flags)
 530 {
 531         if (control_word & CW_Precision) {
 532                 partial_status &= ~(SW_C1 & flags);
 533                 partial_status |= flags;        /* The masked response */
 534                 return 0;
 535         } else {
 536                 EXCEPTION(flags);
 537                 return 1;
 538         }
 539 }
 540
 541 /* This may be called often, so keep it lean */
 542 asmlinkage __visible void set_precision_flag_up(void)
 543 {
 544         if (control_word & CW_Precision)
 545                 partial_status |= (SW_Precision | SW_C1);       /* The masked response */
 546         else
 547                 EXCEPTION(EX_Precision | SW_C1);
 548 }
 549
 550 /* This may be called often, so keep it lean */
 551 asmlinkage __visible void set_precision_flag_down(void)
 552 {
 553         if (control_word & CW_Precision) {      /* The masked response */
 554                 partial_status &= ~SW_C1;
 555                 partial_status |= SW_Precision;
 556         } else
 557                 EXCEPTION(EX_Precision);
 558 }
 559
 560 asmlinkage __visible int denormal_operand(void)
 561 {
 562         if (control_word & CW_Denormal) {       /* The masked response */
 563                 partial_status |= SW_Denorm_Op;
 564                 return TAG_Special;
 565         } else {
 566                 EXCEPTION(EX_Denormal);
 567                 return TAG_Special | FPU_Exception;
 568         }
 569 }
 570
 571 asmlinkage __visible int arith_overflow(FPU_REG *dest)
 572 {
 573         int tag = TAG_Valid;
 574
 575         if (control_word & CW_Overflow) {
 576                 /* The masked response */
 577 /* ###### The response here depends upon the rounding mode */
 578                 reg_copy(&CONST_INF, dest);
 579                 tag = TAG_Special;
 580         } else {
 581                 /* Subtract the magic number from the exponent */
 582                 addexponent(dest, (-3 * (1 << 13)));
 583         }
 584
 585         EXCEPTION(EX_Overflow);
 586         if (control_word & CW_Overflow) {
 587                 /* The overflow exception is masked. */
 588                 /* By definition, precision is lost.
 589                    The roundup bit (C1) is also set because we have
 590                    "rounded" upwards to Infinity. */
 591                 EXCEPTION(EX_Precision | SW_C1);
 592                 return tag;
 593         }
 594
 595         return tag;
 596
 597 }
 598
 599 asmlinkage __visible int arith_underflow(FPU_REG *dest)
 600 {
 601         int tag = TAG_Valid;
 602
 603         if (control_word & CW_Underflow) {
 604                 /* The masked response */
 605                 if (exponent16(dest) <= EXP_UNDER - 63) {
 606                         reg_copy(&CONST_Z, dest);
 607                         partial_status &= ~SW_C1;       /* Round down. */
 608                         tag = TAG_Zero;
 609                 } else {
 610                         stdexp(dest);
 611                 }
 612         } else {
 613                 /* Add the magic number to the exponent. */
 614                 addexponent(dest, (3 * (1 << 13)) + EXTENDED_Ebias);
 615         }
 616
 617         EXCEPTION(EX_Underflow);
 618         if (control_word & CW_Underflow) {
 619                 /* The underflow exception is masked. */
 620                 EXCEPTION(EX_Precision);
 621                 return tag;
 622         }
 623
 624         return tag;
 625
 626 }
 627
 628 void FPU_stack_overflow(void)
 629 {
 630
 631         if (control_word & CW_Invalid) {
 632                 /* The masked response */
 633                 top--;
 634                 FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 635         }
 636
 637         EXCEPTION(EX_StackOver);
 638
 639         return;
 640
 641 }
 642
 643 void FPU_stack_underflow(void)
 644 {
 645
 646         if (control_word & CW_Invalid) {
 647                 /* The masked response */
 648                 FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 649         }
 650
 651         EXCEPTION(EX_StackUnder);
 652
 653         return;
 654
 655 }
 656
 657 void FPU_stack_underflow_i(int i)
 658 {
 659
 660         if (control_word & CW_Invalid) {
 661                 /* The masked response */
 662                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 663         }
 664
 665         EXCEPTION(EX_StackUnder);
 666
 667         return;
 668
 669 }
 670
 671 void FPU_stack_underflow_pop(int i)
 672 {
 673
 674         if (control_word & CW_Invalid) {
 675                 /* The masked response */
 676                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 677                 FPU_pop();
 678         }
 679
 680         EXCEPTION(EX_StackUnder);
 681
 682         return;
 683
 684 }