arch/i386/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
  37 #if 0
  38 void Un_impl(void)
  39 {
  40   u_char byte1, FPU_modrm;
  41   unsigned long address = FPU_ORIG_EIP;
  42
  43   RE_ENTRANT_CHECK_OFF;
  44   /* No need to check access_ok(), we have previously fetched these bytes. */
  45   printk("Unimplemented FPU Opcode at eip=%p : ", (void __user *) address);
  46   if ( FPU_CS == __USER_CS )
  47     {
  48       while ( 1 )
  49         {
  50           FPU_get_user(byte1, (u_char __user *) address);
  51           if ( (byte1 & 0xf8) == 0xd8 ) break;
  52           printk("[%02x]", byte1);
  53           address++;
  54         }
  55       printk("%02x ", byte1);
  56       FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
  57
  58       if (FPU_modrm >= 0300)
  59         printk("%02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8, FPU_modrm & 7);
  60       else
  61         printk("/%d\n", (FPU_modrm >> 3) & 7);
  62     }
  63   else
  64     {
  65       printk("cs selector = %04x\n", FPU_CS);
  66     }
  67
  68   RE_ENTRANT_CHECK_ON;
  69
  70   EXCEPTION(EX_Invalid);
  71
  72 }
  73 #endif  /*  0  */
  74
  75
  76 /*
  77    Called for opcodes which are illegal and which are known to result in a
  78    SIGILL with a real 80486.
  79    */
  80 void FPU_illegal(void)
  81 {
  82   math_abort(FPU_info,SIGILL);
  83 }
  84
  85
  86
  87 void FPU_printall(void)
  88 {
  89   int i;
  90   static const char *tag_desc[] = { "Valid", "Zero", "ERROR", "Empty",
  91                               "DeNorm", "Inf", "NaN" };
  92   u_char byte1, FPU_modrm;
  93   unsigned long address = FPU_ORIG_EIP;
  94
  95   RE_ENTRANT_CHECK_OFF;
  96   /* No need to check access_ok(), we have previously fetched these bytes. */
  97   printk("At %p:", (void *) address);
  98   if ( FPU_CS == __USER_CS )
  99     {
 100 #define MAX_PRINTED_BYTES 20
 101       for ( i = 0; i < MAX_PRINTED_BYTES; i++ )
 102         {
 103           FPU_get_user(byte1, (u_char __user *) address);
 104           if ( (byte1 & 0xf8) == 0xd8 )
 105             {
 106               printk(" %02x", byte1);
 107               break;
 108             }
 109           printk(" [%02x]", byte1);
 110           address++;
 111         }
 112       if ( i == MAX_PRINTED_BYTES )
 113         printk(" [more..]\n");
 114       else
 115         {
 116           FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
 117
 118           if (FPU_modrm >= 0300)
 119             printk(" %02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8, FPU_modrm & 7);
 120           else
 121             printk(" /%d, mod=%d rm=%d\n",
 122                    (FPU_modrm >> 3) & 7, (FPU_modrm >> 6) & 3, FPU_modrm & 7);
 123         }
 124     }
 125   else
 126     {
 127       printk("%04x\n", FPU_CS);
 128     }
 129
 130   partial_status = status_word();
 131
 132 #ifdef DEBUGGING
 133 if ( partial_status & SW_Backward )    printk("SW: backward compatibility\n");
 134 if ( partial_status & SW_C3 )          printk("SW: condition bit 3\n");
 135 if ( partial_status & SW_C2 )          printk("SW: condition bit 2\n");
 136 if ( partial_status & SW_C1 )          printk("SW: condition bit 1\n");
 137 if ( partial_status & SW_C0 )          printk("SW: condition bit 0\n");
 138 if ( partial_status & SW_Summary )     printk("SW: exception summary\n");
 139 if ( partial_status & SW_Stack_Fault ) printk("SW: stack fault\n");
 140 if ( partial_status & SW_Precision )   printk("SW: loss of precision\n");
 141 if ( partial_status & SW_Underflow )   printk("SW: underflow\n");
 142 if ( partial_status & SW_Overflow )    printk("SW: overflow\n");
 143 if ( partial_status & SW_Zero_Div )    printk("SW: divide by zero\n");
 144 if ( partial_status & SW_Denorm_Op )   printk("SW: denormalized operand\n");
 145 if ( partial_status & SW_Invalid )     printk("SW: invalid operation\n");
 146 #endif /* DEBUGGING */
 147
 148   printk(" SW: b=%d st=%ld es=%d sf=%d cc=%d%d%d%d ef=%d%d%d%d%d%d\n",
 149          partial_status & 0x8000 ? 1 : 0,   /* busy */
 150          (partial_status & 0x3800) >> 11,   /* stack top pointer */
 151          partial_status & 0x80 ? 1 : 0,     /* Error summary status */
 152          partial_status & 0x40 ? 1 : 0,     /* Stack flag */
 153          partial_status & SW_C3?1:0, partial_status & SW_C2?1:0, /* cc */
 154          partial_status & SW_C1?1:0, partial_status & SW_C0?1:0, /* cc */
 155          partial_status & SW_Precision?1:0, partial_status & SW_Underflow?1:0,
 156          partial_status & SW_Overflow?1:0, partial_status & SW_Zero_Div?1:0,
 157          partial_status & SW_Denorm_Op?1:0, partial_status & SW_Invalid?1:0);
 158
 159 printk(" CW: ic=%d rc=%ld%ld pc=%ld%ld iem=%d     ef=%d%d%d%d%d%d\n",
 160          control_word & 0x1000 ? 1 : 0,
 161          (control_word & 0x800) >> 11, (control_word & 0x400) >> 10,
 162          (control_word & 0x200) >> 9, (control_word & 0x100) >> 8,
 163          control_word & 0x80 ? 1 : 0,
 164          control_word & SW_Precision?1:0, control_word & SW_Underflow?1:0,
 165          control_word & SW_Overflow?1:0, control_word & SW_Zero_Div?1:0,
 166          control_word & SW_Denorm_Op?1:0, control_word & SW_Invalid?1:0);
 167
 168   for ( i = 0; i < 8; i++ )
 169     {
 170       FPU_REG *r = &st(i);
 171       u_char tagi = FPU_gettagi(i);
 172       switch (tagi)
 173         {
 174         case TAG_Empty:
 175           continue;
 176           break;
 177         case TAG_Zero:
 178         case TAG_Special:
 179           tagi = FPU_Special(r);
 180         case TAG_Valid:
 181           printk("st(%d)  %c .%04lx %04lx %04lx %04lx e%+-6d ", i,
 182                  getsign(r) ? '-' : '+',
 183                  (long)(r->sigh >> 16),
 184                  (long)(r->sigh & 0xFFFF),
 185                  (long)(r->sigl >> 16),
 186                  (long)(r->sigl & 0xFFFF),
 187                  exponent(r) - EXP_BIAS + 1);
 188           break;
 189         default:
 190           printk("Whoops! Error in errors.c: tag%d is %d ", i, tagi);
 191           continue;
 192           break;
 193         }
 194       printk("%s\n", tag_desc[(int) (unsigned) tagi]);
 195     }
 196
 197   RE_ENTRANT_CHECK_ON;
 198
 199 }
 200
 201 static struct {
 202   int type;
 203   const char *name;
 204 } exception_names[] = {
 205   { EX_StackOver, "stack overflow" },
 206   { EX_StackUnder, "stack underflow" },
 207   { EX_Precision, "loss of precision" },
 208   { EX_Underflow, "underflow" },
 209   { EX_Overflow, "overflow" },
 210   { EX_ZeroDiv, "divide by zero" },
 211   { EX_Denormal, "denormalized operand" },
 212   { EX_Invalid, "invalid operation" },
 213   { EX_INTERNAL, "INTERNAL BUG in "FPU_VERSION },
 214   { 0, NULL }
 215 };
 216
 217 /*
 218  EX_INTERNAL is always given with a code which indicates where the
 219  error was detected.
 220
 221  Internal error types:
 222        0x14   in fpu_etc.c
 223        0x1nn  in a *.c file:
 224               0x101  in reg_add_sub.c
 225               0x102  in reg_mul.c
 226               0x104  in poly_atan.c
 227               0x105  in reg_mul.c
 228               0x107  in fpu_trig.c
 229               0x108  in reg_compare.c
 230               0x109  in reg_compare.c
 231               0x110  in reg_add_sub.c
 232               0x111  in fpe_entry.c
 233               0x112  in fpu_trig.c
 234               0x113  in errors.c
 235               0x115  in fpu_trig.c
 236               0x116  in fpu_trig.c
 237               0x117  in fpu_trig.c
 238               0x118  in fpu_trig.c
 239               0x119  in fpu_trig.c
 240               0x120  in poly_atan.c
 241               0x121  in reg_compare.c
 242               0x122  in reg_compare.c
 243               0x123  in reg_compare.c
 244               0x125  in fpu_trig.c
 245               0x126  in fpu_entry.c
 246               0x127  in poly_2xm1.c
 247               0x128  in fpu_entry.c
 248               0x129  in fpu_entry.c
 249               0x130  in get_address.c
 250               0x131  in get_address.c
 251               0x132  in get_address.c
 252               0x133  in get_address.c
 253               0x140  in load_store.c
 254               0x141  in load_store.c
 255               0x150  in poly_sin.c
 256               0x151  in poly_sin.c
 257               0x160  in reg_ld_str.c
 258               0x161  in reg_ld_str.c
 259               0x162  in reg_ld_str.c
 260               0x163  in reg_ld_str.c
 261               0x164  in reg_ld_str.c
 262               0x170  in fpu_tags.c
 263               0x171  in fpu_tags.c
 264               0x172  in fpu_tags.c
 265               0x180  in reg_convert.c
 266        0x2nn  in an *.S file:
 267               0x201  in reg_u_add.S
 268               0x202  in reg_u_div.S
 269               0x203  in reg_u_div.S
 270               0x204  in reg_u_div.S
 271               0x205  in reg_u_mul.S
 272               0x206  in reg_u_sub.S
 273               0x207  in wm_sqrt.S
 274               0x208  in reg_div.S
 275               0x209  in reg_u_sub.S
 276               0x210  in reg_u_sub.S
 277               0x211  in reg_u_sub.S
 278               0x212  in reg_u_sub.S
 279               0x213  in wm_sqrt.S
 280               0x214  in wm_sqrt.S
 281               0x215  in wm_sqrt.S
 282               0x220  in reg_norm.S
 283               0x221  in reg_norm.S
 284               0x230  in reg_round.S
 285               0x231  in reg_round.S
 286               0x232  in reg_round.S
 287               0x233  in reg_round.S
 288               0x234  in reg_round.S
 289               0x235  in reg_round.S
 290               0x236  in reg_round.S
 291               0x240  in div_Xsig.S
 292               0x241  in div_Xsig.S
 293               0x242  in div_Xsig.S
 294  */
 295
 296 asmlinkage void FPU_exception(int n)
 297 {
 298   int i, int_type;
 299
 300   int_type = 0;         /* Needed only to stop compiler warnings */
 301   if ( n & EX_INTERNAL )
 302     {
 303       int_type = n - EX_INTERNAL;
 304       n = EX_INTERNAL;
 305       /* Set lots of exception bits! */
 306       partial_status |= (SW_Exc_Mask | SW_Summary | SW_Backward);
 307     }
 308   else
 309     {
 310       /* Extract only the bits which we use to set the status word */
 311       n &= (SW_Exc_Mask);
 312       /* Set the corresponding exception bit */
 313       partial_status |= n;
 314       /* Set summary bits iff exception isn't masked */
 315       if ( partial_status & ~control_word & CW_Exceptions )
 316         partial_status |= (SW_Summary | SW_Backward);
 317       if ( n & (SW_Stack_Fault | EX_Precision) )
 318         {
 319           if ( !(n & SW_C1) )
 320             /* This bit distinguishes over- from underflow for a stack fault,
 321                and roundup from round-down for precision loss. */
 322             partial_status &= ~SW_C1;
 323         }
 324     }
 325
 326   RE_ENTRANT_CHECK_OFF;
 327   if ( (~control_word & n & CW_Exceptions) || (n == EX_INTERNAL) )
 328     {
 329 #ifdef PRINT_MESSAGES
 330       /* My message from the sponsor */
 331       printk(FPU_VERSION" "__DATE__" (C) W. Metzenthen.\n");
 332 #endif /* PRINT_MESSAGES */
 333
 334       /* Get a name string for error reporting */
 335       for (i=0; exception_names[i].type; i++)
 336         if ( (exception_names[i].type & n) == exception_names[i].type )
 337           break;
 338
 339       if (exception_names[i].type)
 340         {
 341 #ifdef PRINT_MESSAGES
 342           printk("FP Exception: %s!\n", exception_names[i].name);
 343 #endif /* PRINT_MESSAGES */
 344         }
 345       else
 346         printk("FPU emulator: Unknown Exception: 0x%04x!\n", n);
 347
 348       if ( n == EX_INTERNAL )
 349         {
 350           printk("FPU emulator: Internal error type 0x%04x\n", int_type);
 351           FPU_printall();
 352         }
 353 #ifdef PRINT_MESSAGES
 354       else
 355         FPU_printall();
 356 #endif /* PRINT_MESSAGES */
 357
 358       /*
 359        * The 80486 generates an interrupt on the next non-control FPU
 360        * instruction. So we need some means of flagging it.
 361        * We use the ES (Error Summary) bit for this.
 362        */
 363     }
 364   RE_ENTRANT_CHECK_ON;
 365
 366 #ifdef __DEBUG__
 367   math_abort(FPU_info,SIGFPE);
 368 #endif /* __DEBUG__ */
 369
 370 }
 371
 372
 373 /* Real operation attempted on a NaN. */
 374 /* Returns < 0 if the exception is unmasked */
 375 int real_1op_NaN(FPU_REG *a)
 376 {
 377   int signalling, isNaN;
 378
 379   isNaN = (exponent(a) == EXP_OVER) && (a->sigh & 0x80000000);
 380
 381   /* The default result for the case of two "equal" NaNs (signs may
 382      differ) is chosen to reproduce 80486 behaviour */
 383   signalling = isNaN && !(a->sigh & 0x40000000);
 384
 385   if ( !signalling )
 386     {
 387       if ( !isNaN )  /* pseudo-NaN, or other unsupported? */
 388         {
 389           if ( control_word & CW_Invalid )
 390             {
 391               /* Masked response */
 392               reg_copy(&CONST_QNaN, a);
 393             }
 394           EXCEPTION(EX_Invalid);
 395           return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 396         }
 397       return TAG_Special;
 398     }
 399
 400   if ( control_word & CW_Invalid )
 401     {
 402       /* The masked response */
 403       if ( !(a->sigh & 0x80000000) )  /* pseudo-NaN ? */
 404         {
 405           reg_copy(&CONST_QNaN, a);
 406         }
 407       /* ensure a Quiet NaN */
 408       a->sigh |= 0x40000000;
 409     }
 410
 411   EXCEPTION(EX_Invalid);
 412
 413   return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 414 }
 415
 416
 417 /* Real operation attempted on two operands, one a NaN. */
 418 /* Returns < 0 if the exception is unmasked */
 419 int real_2op_NaN(FPU_REG const *b, u_char tagb,
 420                  int deststnr,
 421                  FPU_REG const *defaultNaN)
 422 {
 423   FPU_REG *dest = &st(deststnr);
 424   FPU_REG const *a = dest;
 425   u_char taga = FPU_gettagi(deststnr);
 426   FPU_REG const *x;
 427   int signalling, unsupported;
 428
 429   if ( taga == TAG_Special )
 430     taga = FPU_Special(a);
 431   if ( tagb == TAG_Special )
 432     tagb = FPU_Special(b);
 433
 434   /* TW_NaN is also used for unsupported data types. */
 435   unsupported = ((taga == TW_NaN)
 436                  && !((exponent(a) == EXP_OVER) && (a->sigh & 0x80000000)))
 437     || ((tagb == TW_NaN)
 438         && !((exponent(b) == EXP_OVER) && (b->sigh & 0x80000000)));
 439   if ( unsupported )
 440     {
 441       if ( control_word & CW_Invalid )
 442         {
 443           /* Masked response */
 444           FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 445         }
 446       EXCEPTION(EX_Invalid);
 447       return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 448     }
 449
 450   if (taga == TW_NaN)
 451     {
 452       x = a;
 453       if (tagb == TW_NaN)
 454         {
 455           signalling = !(a->sigh & b->sigh & 0x40000000);
 456           if ( significand(b) > significand(a) )
 457             x = b;
 458           else if ( significand(b) == significand(a) )
 459             {
 460               /* The default result for the case of two "equal" NaNs (signs may
 461                  differ) is chosen to reproduce 80486 behaviour */
 462               x = defaultNaN;
 463             }
 464         }
 465       else
 466         {
 467           /* return the quiet version of the NaN in a */
 468           signalling = !(a->sigh & 0x40000000);
 469         }
 470     }
 471   else
 472 #ifdef PARANOID
 473     if (tagb == TW_NaN)
 474 #endif /* PARANOID */
 475     {
 476       signalling = !(b->sigh & 0x40000000);
 477       x = b;
 478     }
 479 #ifdef PARANOID
 480   else
 481     {
 482       signalling = 0;
 483       EXCEPTION(EX_INTERNAL|0x113);
 484       x = &CONST_QNaN;
 485     }
 486 #endif /* PARANOID */
 487
 488   if ( (!signalling) || (control_word & CW_Invalid) )
 489     {
 490       if ( ! x )
 491         x = b;
 492
 493       if ( !(x->sigh & 0x80000000) )  /* pseudo-NaN ? */
 494         x = &CONST_QNaN;
 495
 496       FPU_copy_to_regi(x, TAG_Special, deststnr);
 497
 498       if ( !signalling )
 499         return TAG_Special;
 500
 501       /* ensure a Quiet NaN */
 502       dest->sigh |= 0x40000000;
 503     }
 504
 505   EXCEPTION(EX_Invalid);
 506
 507   return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 508 }
 509
 510
 511 /* Invalid arith operation on Valid registers */
 512 /* Returns < 0 if the exception is unmasked */
 513 asmlinkage int arith_invalid(int deststnr)
 514 {
 515
 516   EXCEPTION(EX_Invalid);
 517
 518   if ( control_word & CW_Invalid )
 519     {
 520       /* The masked response */
 521       FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 522     }
 523
 524   return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Valid;
 525
 526 }
 527
 528
 529 /* Divide a finite number by zero */
 530 asmlinkage int FPU_divide_by_zero(int deststnr, u_char sign)
 531 {
 532   FPU_REG *dest = &st(deststnr);
 533   int tag = TAG_Valid;
 534
 535   if ( control_word & CW_ZeroDiv )
 536     {
 537       /* The masked response */
 538       FPU_copy_to_regi(&CONST_INF, TAG_Special, deststnr);
 539       setsign(dest, sign);
 540       tag = TAG_Special;
 541     }
 542
 543   EXCEPTION(EX_ZeroDiv);
 544
 545   return (!(control_word & CW_ZeroDiv) ? FPU_Exception : 0) | tag;
 546
 547 }
 548
 549
 550 /* This may be called often, so keep it lean */
 551 int set_precision_flag(int flags)
 552 {
 553   if ( control_word & CW_Precision )
 554     {
 555       partial_status &= ~(SW_C1 & flags);
 556       partial_status |= flags;   /* The masked response */
 557       return 0;
 558     }
 559   else
 560     {
 561       EXCEPTION(flags);
 562       return 1;
 563     }
 564 }
 565
 566
 567 /* This may be called often, so keep it lean */
 568 asmlinkage void set_precision_flag_up(void)
 569 {
 570   if ( control_word & CW_Precision )
 571     partial_status |= (SW_Precision | SW_C1);   /* The masked response */
 572   else
 573     EXCEPTION(EX_Precision | SW_C1);
 574 }
 575
 576
 577 /* This may be called often, so keep it lean */
 578 asmlinkage void set_precision_flag_down(void)
 579 {
 580   if ( control_word & CW_Precision )
 581     {   /* The masked response */
 582       partial_status &= ~SW_C1;
 583       partial_status |= SW_Precision;
 584     }
 585   else
 586     EXCEPTION(EX_Precision);
 587 }
 588
 589
 590 asmlinkage int denormal_operand(void)
 591 {
 592   if ( control_word & CW_Denormal )
 593     {   /* The masked response */
 594       partial_status |= SW_Denorm_Op;
 595       return TAG_Special;
 596     }
 597   else
 598     {
 599       EXCEPTION(EX_Denormal);
 600       return TAG_Special | FPU_Exception;
 601     }
 602 }
 603
 604
 605 asmlinkage int arith_overflow(FPU_REG *dest)
 606 {
 607   int tag = TAG_Valid;
 608
 609   if ( control_word & CW_Overflow )
 610     {
 611       /* The masked response */
 612 /* ###### The response here depends upon the rounding mode */
 613       reg_copy(&CONST_INF, dest);
 614       tag = TAG_Special;
 615     }
 616   else
 617     {
 618       /* Subtract the magic number from the exponent */
 619       addexponent(dest, (-3 * (1 << 13)));
 620     }
 621
 622   EXCEPTION(EX_Overflow);
 623   if ( control_word & CW_Overflow )
 624     {
 625       /* The overflow exception is masked. */
 626       /* By definition, precision is lost.
 627          The roundup bit (C1) is also set because we have
 628          "rounded" upwards to Infinity. */
 629       EXCEPTION(EX_Precision | SW_C1);
 630       return tag;
 631     }
 632
 633   return tag;
 634
 635 }
 636
 637
 638 asmlinkage int arith_underflow(FPU_REG *dest)
 639 {
 640   int tag = TAG_Valid;
 641
 642   if ( control_word & CW_Underflow )
 643     {
 644       /* The masked response */
 645       if ( exponent16(dest) <= EXP_UNDER - 63 )
 646         {
 647           reg_copy(&CONST_Z, dest);
 648           partial_status &= ~SW_C1;       /* Round down. */
 649           tag = TAG_Zero;
 650         }
 651       else
 652         {
 653           stdexp(dest);
 654         }
 655     }
 656   else
 657     {
 658       /* Add the magic number to the exponent. */
 659       addexponent(dest, (3 * (1 << 13)) + EXTENDED_Ebias);
 660     }
 661
 662   EXCEPTION(EX_Underflow);
 663   if ( control_word & CW_Underflow )
 664     {
 665       /* The underflow exception is masked. */
 666       EXCEPTION(EX_Precision);
 667       return tag;
 668     }
 669
 670   return tag;
 671
 672 }
 673
 674
 675 void FPU_stack_overflow(void)
 676 {
 677
 678  if ( control_word & CW_Invalid )
 679     {
 680       /* The masked response */
 681       top--;
 682       FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 683     }
 684
 685   EXCEPTION(EX_StackOver);
 686
 687   return;
 688
 689 }
 690
 691
 692 void FPU_stack_underflow(void)
 693 {
 694
 695  if ( control_word & CW_Invalid )
 696     {
 697       /* The masked response */
 698       FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 699     }
 700
 701   EXCEPTION(EX_StackUnder);
 702
 703   return;
 704
 705 }
 706
 707
 708 void FPU_stack_underflow_i(int i)
 709 {
 710
 711  if ( control_word & CW_Invalid )
 712     {
 713       /* The masked response */
 714       FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 715     }
 716
 717   EXCEPTION(EX_StackUnder);
 718
 719   return;
 720
 721 }
 722
 723
 724 void FPU_stack_underflow_pop(int i)
 725 {
 726
 727  if ( control_word & CW_Invalid )
 728     {
 729       /* The masked response */
 730       FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 731       FPU_pop();
 732     }
 733
 734   EXCEPTION(EX_StackUnder);
 735
 736   return;
 737
 738 }
 739