root/arch/x86/math-emu/errors.c

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DEFINITIONS

This source file includes following definitions.
  1. Un_impl
  2. FPU_illegal
  3. FPU_printall
  4. FPU_exception
  5. real_1op_NaN
  6. real_2op_NaN
  7. arith_invalid
  8. FPU_divide_by_zero
  9. set_precision_flag
  10. set_precision_flag_up
  11. set_precision_flag_down
  12. denormal_operand
  13. arith_overflow
  14. arith_underflow
  15. FPU_stack_overflow
  16. FPU_stack_underflow
  17. FPU_stack_underflow_i
  18. FPU_stack_underflow_pop
   1 // SPDX-License-Identifier: GPL-2.0
   2 /*---------------------------------------------------------------------------+
   3  |  errors.c                                                                 |
   4  |                                                                           |
   5  |  The error handling functions for wm-FPU-emu                              |
   6  |                                                                           |
   7  | Copyright (C) 1992,1993,1994,1996                                         |
   8  |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
   9  |                  E-mail   billm@jacobi.maths.monash.edu.au                |
  10  |                                                                           |
  11  |                                                                           |
  12  +---------------------------------------------------------------------------*/
  13 
  14 /*---------------------------------------------------------------------------+
  15  | Note:                                                                     |
  16  |    The file contains code which accesses user memory.                     |
  17  |    Emulator static data may change when user memory is accessed, due to   |
  18  |    other processes using the emulator while swapping is in progress.      |
  19  +---------------------------------------------------------------------------*/
  20 
  21 #include <linux/signal.h>
  22 
  23 #include <linux/uaccess.h>
  24 
  25 #include "fpu_emu.h"
  26 #include "fpu_system.h"
  27 #include "exception.h"
  28 #include "status_w.h"
  29 #include "control_w.h"
  30 #include "reg_constant.h"
  31 #include "version.h"
  32 
  33 /* */
  34 #undef PRINT_MESSAGES
  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                 while (1) {
  48                         FPU_get_user(byte1, (u_char __user *) address);
  49                         if ((byte1 & 0xf8) == 0xd8)
  50                                 break;
  51                         printk("[%02x]", byte1);
  52                         address++;
  53                 }
  54                 printk("%02x ", byte1);
  55                 FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
  56 
  57                 if (FPU_modrm >= 0300)
  58                         printk("%02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8,
  59                                FPU_modrm & 7);
  60                 else
  61                         printk("/%d\n", (FPU_modrm >> 3) & 7);
  62         } else {
  63                 printk("cs selector = %04x\n", FPU_CS);
  64         }
  65 
  66         RE_ENTRANT_CHECK_ON;
  67 
  68         EXCEPTION(EX_Invalid);
  69 
  70 }
  71 #endif /*  0  */
  72 
  73 /*
  74    Called for opcodes which are illegal and which are known to result in a
  75    SIGILL with a real 80486.
  76    */
  77 void FPU_illegal(void)
  78 {
  79         math_abort(FPU_info, SIGILL);
  80 }
  81 
  82 void FPU_printall(void)
  83 {
  84         int i;
  85         static const char *tag_desc[] = { "Valid", "Zero", "ERROR", "Empty",
  86                 "DeNorm", "Inf", "NaN"
  87         };
  88         u_char byte1, FPU_modrm;
  89         unsigned long address = FPU_ORIG_EIP;
  90 
  91         RE_ENTRANT_CHECK_OFF;
  92         /* No need to check access_ok(), we have previously fetched these bytes. */
  93         printk("At %p:", (void *)address);
  94         if (FPU_CS == __USER_CS) {
  95 #define MAX_PRINTED_BYTES 20
  96                 for (i = 0; i < MAX_PRINTED_BYTES; i++) {
  97                         FPU_get_user(byte1, (u_char __user *) address);
  98                         if ((byte1 & 0xf8) == 0xd8) {
  99                                 printk(" %02x", byte1);
 100                                 break;
 101                         }
 102                         printk(" [%02x]", byte1);
 103                         address++;
 104                 }
 105                 if (i == MAX_PRINTED_BYTES)
 106                         printk(" [more..]\n");
 107                 else {
 108                         FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
 109 
 110                         if (FPU_modrm >= 0300)
 111                                 printk(" %02x (%02x+%d)\n", FPU_modrm,
 112                                        FPU_modrm & 0xf8, FPU_modrm & 7);
 113                         else
 114                                 printk(" /%d, mod=%d rm=%d\n",
 115                                        (FPU_modrm >> 3) & 7,
 116                                        (FPU_modrm >> 6) & 3, FPU_modrm & 7);
 117                 }
 118         } else {
 119                 printk("%04x\n", FPU_CS);
 120         }
 121 
 122         partial_status = status_word();
 123 
 124 #ifdef DEBUGGING
 125         if (partial_status & SW_Backward)
 126                 printk("SW: backward compatibility\n");
 127         if (partial_status & SW_C3)
 128                 printk("SW: condition bit 3\n");
 129         if (partial_status & SW_C2)
 130                 printk("SW: condition bit 2\n");
 131         if (partial_status & SW_C1)
 132                 printk("SW: condition bit 1\n");
 133         if (partial_status & SW_C0)
 134                 printk("SW: condition bit 0\n");
 135         if (partial_status & SW_Summary)
 136                 printk("SW: exception summary\n");
 137         if (partial_status & SW_Stack_Fault)
 138                 printk("SW: stack fault\n");
 139         if (partial_status & SW_Precision)
 140                 printk("SW: loss of precision\n");
 141         if (partial_status & SW_Underflow)
 142                 printk("SW: underflow\n");
 143         if (partial_status & SW_Overflow)
 144                 printk("SW: overflow\n");
 145         if (partial_status & SW_Zero_Div)
 146                 printk("SW: divide by zero\n");
 147         if (partial_status & SW_Denorm_Op)
 148                 printk("SW: denormalized operand\n");
 149         if (partial_status & SW_Invalid)
 150                 printk("SW: invalid operation\n");
 151 #endif /* DEBUGGING */
 152 
 153         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 */
 154                (partial_status & 0x3800) >> 11, /* stack top pointer */
 155                partial_status & 0x80 ? 1 : 0,   /* Error summary status */
 156                partial_status & 0x40 ? 1 : 0,   /* Stack flag */
 157                partial_status & SW_C3 ? 1 : 0, partial_status & SW_C2 ? 1 : 0,  /* cc */
 158                partial_status & SW_C1 ? 1 : 0, partial_status & SW_C0 ? 1 : 0,  /* cc */
 159                partial_status & SW_Precision ? 1 : 0,
 160                partial_status & SW_Underflow ? 1 : 0,
 161                partial_status & SW_Overflow ? 1 : 0,
 162                partial_status & SW_Zero_Div ? 1 : 0,
 163                partial_status & SW_Denorm_Op ? 1 : 0,
 164                partial_status & SW_Invalid ? 1 : 0);
 165 
 166         printk(" CW: ic=%d rc=%d%d pc=%d%d iem=%d     ef=%d%d%d%d%d%d\n",
 167                control_word & 0x1000 ? 1 : 0,
 168                (control_word & 0x800) >> 11, (control_word & 0x400) >> 10,
 169                (control_word & 0x200) >> 9, (control_word & 0x100) >> 8,
 170                control_word & 0x80 ? 1 : 0,
 171                control_word & SW_Precision ? 1 : 0,
 172                control_word & SW_Underflow ? 1 : 0,
 173                control_word & SW_Overflow ? 1 : 0,
 174                control_word & SW_Zero_Div ? 1 : 0,
 175                control_word & SW_Denorm_Op ? 1 : 0,
 176                control_word & SW_Invalid ? 1 : 0);
 177 
 178         for (i = 0; i < 8; i++) {
 179                 FPU_REG *r = &st(i);
 180                 u_char tagi = FPU_gettagi(i);
 181 
 182                 switch (tagi) {
 183                 case TAG_Empty:
 184                         continue;
 185                 case TAG_Zero:
 186                 case TAG_Special:
 187                         /* Update tagi for the printk below */
 188                         tagi = FPU_Special(r);
 189                         /* fall through */
 190                 case TAG_Valid:
 191                         printk("st(%d)  %c .%04lx %04lx %04lx %04lx e%+-6d ", i,
 192                                getsign(r) ? '-' : '+',
 193                                (long)(r->sigh >> 16),
 194                                (long)(r->sigh & 0xFFFF),
 195                                (long)(r->sigl >> 16),
 196                                (long)(r->sigl & 0xFFFF),
 197                                exponent(r) - EXP_BIAS + 1);
 198                         break;
 199                 default:
 200                         printk("Whoops! Error in errors.c: tag%d is %d ", i,
 201                                tagi);
 202                         continue;
 203                 }
 204                 printk("%s\n", tag_desc[(int)(unsigned)tagi]);
 205         }
 206 
 207         RE_ENTRANT_CHECK_ON;
 208 
 209 }
 210 
 211 static struct {
 212         int type;
 213         const char *name;
 214 } exception_names[] = {
 215         {
 216         EX_StackOver, "stack overflow"}, {
 217         EX_StackUnder, "stack underflow"}, {
 218         EX_Precision, "loss of precision"}, {
 219         EX_Underflow, "underflow"}, {
 220         EX_Overflow, "overflow"}, {
 221         EX_ZeroDiv, "divide by zero"}, {
 222         EX_Denormal, "denormalized operand"}, {
 223         EX_Invalid, "invalid operation"}, {
 224         EX_INTERNAL, "INTERNAL BUG in " FPU_VERSION}, {
 225         0, NULL}
 226 };
 227 
 228 /*
 229  EX_INTERNAL is always given with a code which indicates where the
 230  error was detected.
 231 
 232  Internal error types:
 233        0x14   in fpu_etc.c
 234        0x1nn  in a *.c file:
 235               0x101  in reg_add_sub.c
 236               0x102  in reg_mul.c
 237               0x104  in poly_atan.c
 238               0x105  in reg_mul.c
 239               0x107  in fpu_trig.c
 240               0x108  in reg_compare.c
 241               0x109  in reg_compare.c
 242               0x110  in reg_add_sub.c
 243               0x111  in fpe_entry.c
 244               0x112  in fpu_trig.c
 245               0x113  in errors.c
 246               0x115  in fpu_trig.c
 247               0x116  in fpu_trig.c
 248               0x117  in fpu_trig.c
 249               0x118  in fpu_trig.c
 250               0x119  in fpu_trig.c
 251               0x120  in poly_atan.c
 252               0x121  in reg_compare.c
 253               0x122  in reg_compare.c
 254               0x123  in reg_compare.c
 255               0x125  in fpu_trig.c
 256               0x126  in fpu_entry.c
 257               0x127  in poly_2xm1.c
 258               0x128  in fpu_entry.c
 259               0x129  in fpu_entry.c
 260               0x130  in get_address.c
 261               0x131  in get_address.c
 262               0x132  in get_address.c
 263               0x133  in get_address.c
 264               0x140  in load_store.c
 265               0x141  in load_store.c
 266               0x150  in poly_sin.c
 267               0x151  in poly_sin.c
 268               0x160  in reg_ld_str.c
 269               0x161  in reg_ld_str.c
 270               0x162  in reg_ld_str.c
 271               0x163  in reg_ld_str.c
 272               0x164  in reg_ld_str.c
 273               0x170  in fpu_tags.c
 274               0x171  in fpu_tags.c
 275               0x172  in fpu_tags.c
 276               0x180  in reg_convert.c
 277        0x2nn  in an *.S file:
 278               0x201  in reg_u_add.S
 279               0x202  in reg_u_div.S
 280               0x203  in reg_u_div.S
 281               0x204  in reg_u_div.S
 282               0x205  in reg_u_mul.S
 283               0x206  in reg_u_sub.S
 284               0x207  in wm_sqrt.S
 285               0x208  in reg_div.S
 286               0x209  in reg_u_sub.S
 287               0x210  in reg_u_sub.S
 288               0x211  in reg_u_sub.S
 289               0x212  in reg_u_sub.S
 290               0x213  in wm_sqrt.S
 291               0x214  in wm_sqrt.S
 292               0x215  in wm_sqrt.S
 293               0x220  in reg_norm.S
 294               0x221  in reg_norm.S
 295               0x230  in reg_round.S
 296               0x231  in reg_round.S
 297               0x232  in reg_round.S
 298               0x233  in reg_round.S
 299               0x234  in reg_round.S
 300               0x235  in reg_round.S
 301               0x236  in reg_round.S
 302               0x240  in div_Xsig.S
 303               0x241  in div_Xsig.S
 304               0x242  in div_Xsig.S
 305  */
 306 
 307 asmlinkage __visible void FPU_exception(int n)
 308 {
 309         int i, int_type;
 310 
 311         int_type = 0;           /* Needed only to stop compiler warnings */
 312         if (n & EX_INTERNAL) {
 313                 int_type = n - EX_INTERNAL;
 314                 n = EX_INTERNAL;
 315                 /* Set lots of exception bits! */
 316                 partial_status |= (SW_Exc_Mask | SW_Summary | SW_Backward);
 317         } else {
 318                 /* Extract only the bits which we use to set the status word */
 319                 n &= (SW_Exc_Mask);
 320                 /* Set the corresponding exception bit */
 321                 partial_status |= n;
 322                 /* Set summary bits iff exception isn't masked */
 323                 if (partial_status & ~control_word & CW_Exceptions)
 324                         partial_status |= (SW_Summary | SW_Backward);
 325                 if (n & (SW_Stack_Fault | EX_Precision)) {
 326                         if (!(n & SW_C1))
 327                                 /* This bit distinguishes over- from underflow for a stack fault,
 328                                    and roundup from round-down for precision loss. */
 329                                 partial_status &= ~SW_C1;
 330                 }
 331         }
 332 
 333         RE_ENTRANT_CHECK_OFF;
 334         if ((~control_word & n & CW_Exceptions) || (n == EX_INTERNAL)) {
 335                 /* Get a name string for error reporting */
 336                 for (i = 0; exception_names[i].type; i++)
 337                         if ((exception_names[i].type & n) ==
 338                             exception_names[i].type)
 339                                 break;
 340 
 341                 if (exception_names[i].type) {
 342 #ifdef PRINT_MESSAGES
 343                         printk("FP Exception: %s!\n", exception_names[i].name);
 344 #endif /* PRINT_MESSAGES */
 345                 } else
 346                         printk("FPU emulator: Unknown Exception: 0x%04x!\n", n);
 347 
 348                 if (n == EX_INTERNAL) {
 349                         printk("FPU emulator: Internal error type 0x%04x\n",
 350                                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 /* Real operation attempted on a NaN. */
 373 /* Returns < 0 if the exception is unmasked */
 374 int real_1op_NaN(FPU_REG *a)
 375 {
 376         int signalling, isNaN;
 377 
 378         isNaN = (exponent(a) == EXP_OVER) && (a->sigh & 0x80000000);
 379 
 380         /* The default result for the case of two "equal" NaNs (signs may
 381            differ) is chosen to reproduce 80486 behaviour */
 382         signalling = isNaN && !(a->sigh & 0x40000000);
 383 
 384         if (!signalling) {
 385                 if (!isNaN) {   /* pseudo-NaN, or other unsupported? */
 386                         if (control_word & CW_Invalid) {
 387                                 /* Masked response */
 388                                 reg_copy(&CONST_QNaN, a);
 389                         }
 390                         EXCEPTION(EX_Invalid);
 391                         return (!(control_word & CW_Invalid) ? FPU_Exception :
 392                                 0) | TAG_Special;
 393                 }
 394                 return TAG_Special;
 395         }
 396 
 397         if (control_word & CW_Invalid) {
 398                 /* The masked response */
 399                 if (!(a->sigh & 0x80000000)) {  /* pseudo-NaN ? */
 400                         reg_copy(&CONST_QNaN, a);
 401                 }
 402                 /* ensure a Quiet NaN */
 403                 a->sigh |= 0x40000000;
 404         }
 405 
 406         EXCEPTION(EX_Invalid);
 407 
 408         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 409 }
 410 
 411 /* Real operation attempted on two operands, one a NaN. */
 412 /* Returns < 0 if the exception is unmasked */
 413 int real_2op_NaN(FPU_REG const *b, u_char tagb,
 414                  int deststnr, FPU_REG const *defaultNaN)
 415 {
 416         FPU_REG *dest = &st(deststnr);
 417         FPU_REG const *a = dest;
 418         u_char taga = FPU_gettagi(deststnr);
 419         FPU_REG const *x;
 420         int signalling, unsupported;
 421 
 422         if (taga == TAG_Special)
 423                 taga = FPU_Special(a);
 424         if (tagb == TAG_Special)
 425                 tagb = FPU_Special(b);
 426 
 427         /* TW_NaN is also used for unsupported data types. */
 428         unsupported = ((taga == TW_NaN)
 429                        && !((exponent(a) == EXP_OVER)
 430                             && (a->sigh & 0x80000000)))
 431             || ((tagb == TW_NaN)
 432                 && !((exponent(b) == EXP_OVER) && (b->sigh & 0x80000000)));
 433         if (unsupported) {
 434                 if (control_word & CW_Invalid) {
 435                         /* Masked response */
 436                         FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 437                 }
 438                 EXCEPTION(EX_Invalid);
 439                 return (!(control_word & CW_Invalid) ? FPU_Exception : 0) |
 440                     TAG_Special;
 441         }
 442 
 443         if (taga == TW_NaN) {
 444                 x = a;
 445                 if (tagb == TW_NaN) {
 446                         signalling = !(a->sigh & b->sigh & 0x40000000);
 447                         if (significand(b) > significand(a))
 448                                 x = b;
 449                         else if (significand(b) == significand(a)) {
 450                                 /* The default result for the case of two "equal" NaNs (signs may
 451                                    differ) is chosen to reproduce 80486 behaviour */
 452                                 x = defaultNaN;
 453                         }
 454                 } else {
 455                         /* return the quiet version of the NaN in a */
 456                         signalling = !(a->sigh & 0x40000000);
 457                 }
 458         } else
 459 #ifdef PARANOID
 460         if (tagb == TW_NaN)
 461 #endif /* PARANOID */
 462         {
 463                 signalling = !(b->sigh & 0x40000000);
 464                 x = b;
 465         }
 466 #ifdef PARANOID
 467         else {
 468                 signalling = 0;
 469                 EXCEPTION(EX_INTERNAL | 0x113);
 470                 x = &CONST_QNaN;
 471         }
 472 #endif /* PARANOID */
 473 
 474         if ((!signalling) || (control_word & CW_Invalid)) {
 475                 if (!x)
 476                         x = b;
 477 
 478                 if (!(x->sigh & 0x80000000))    /* pseudo-NaN ? */
 479                         x = &CONST_QNaN;
 480 
 481                 FPU_copy_to_regi(x, TAG_Special, deststnr);
 482 
 483                 if (!signalling)
 484                         return TAG_Special;
 485 
 486                 /* ensure a Quiet NaN */
 487                 dest->sigh |= 0x40000000;
 488         }
 489 
 490         EXCEPTION(EX_Invalid);
 491 
 492         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
 493 }
 494 
 495 /* Invalid arith operation on Valid registers */
 496 /* Returns < 0 if the exception is unmasked */
 497 asmlinkage __visible int arith_invalid(int deststnr)
 498 {
 499 
 500         EXCEPTION(EX_Invalid);
 501 
 502         if (control_word & CW_Invalid) {
 503                 /* The masked response */
 504                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
 505         }
 506 
 507         return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Valid;
 508 
 509 }
 510 
 511 /* Divide a finite number by zero */
 512 asmlinkage __visible int FPU_divide_by_zero(int deststnr, u_char sign)
 513 {
 514         FPU_REG *dest = &st(deststnr);
 515         int tag = TAG_Valid;
 516 
 517         if (control_word & CW_ZeroDiv) {
 518                 /* The masked response */
 519                 FPU_copy_to_regi(&CONST_INF, TAG_Special, deststnr);
 520                 setsign(dest, sign);
 521                 tag = TAG_Special;
 522         }
 523 
 524         EXCEPTION(EX_ZeroDiv);
 525 
 526         return (!(control_word & CW_ZeroDiv) ? FPU_Exception : 0) | tag;
 527 
 528 }
 529 
 530 /* This may be called often, so keep it lean */
 531 int set_precision_flag(int flags)
 532 {
 533         if (control_word & CW_Precision) {
 534                 partial_status &= ~(SW_C1 & flags);
 535                 partial_status |= flags;        /* The masked response */
 536                 return 0;
 537         } else {
 538                 EXCEPTION(flags);
 539                 return 1;
 540         }
 541 }
 542 
 543 /* This may be called often, so keep it lean */
 544 asmlinkage __visible void set_precision_flag_up(void)
 545 {
 546         if (control_word & CW_Precision)
 547                 partial_status |= (SW_Precision | SW_C1);       /* The masked response */
 548         else
 549                 EXCEPTION(EX_Precision | SW_C1);
 550 }
 551 
 552 /* This may be called often, so keep it lean */
 553 asmlinkage __visible void set_precision_flag_down(void)
 554 {
 555         if (control_word & CW_Precision) {      /* The masked response */
 556                 partial_status &= ~SW_C1;
 557                 partial_status |= SW_Precision;
 558         } else
 559                 EXCEPTION(EX_Precision);
 560 }
 561 
 562 asmlinkage __visible int denormal_operand(void)
 563 {
 564         if (control_word & CW_Denormal) {       /* The masked response */
 565                 partial_status |= SW_Denorm_Op;
 566                 return TAG_Special;
 567         } else {
 568                 EXCEPTION(EX_Denormal);
 569                 return TAG_Special | FPU_Exception;
 570         }
 571 }
 572 
 573 asmlinkage __visible int arith_overflow(FPU_REG *dest)
 574 {
 575         int tag = TAG_Valid;
 576 
 577         if (control_word & CW_Overflow) {
 578                 /* The masked response */
 579 /* ###### The response here depends upon the rounding mode */
 580                 reg_copy(&CONST_INF, dest);
 581                 tag = TAG_Special;
 582         } else {
 583                 /* Subtract the magic number from the exponent */
 584                 addexponent(dest, (-3 * (1 << 13)));
 585         }
 586 
 587         EXCEPTION(EX_Overflow);
 588         if (control_word & CW_Overflow) {
 589                 /* The overflow exception is masked. */
 590                 /* By definition, precision is lost.
 591                    The roundup bit (C1) is also set because we have
 592                    "rounded" upwards to Infinity. */
 593                 EXCEPTION(EX_Precision | SW_C1);
 594                 return tag;
 595         }
 596 
 597         return tag;
 598 
 599 }
 600 
 601 asmlinkage __visible int arith_underflow(FPU_REG *dest)
 602 {
 603         int tag = TAG_Valid;
 604 
 605         if (control_word & CW_Underflow) {
 606                 /* The masked response */
 607                 if (exponent16(dest) <= EXP_UNDER - 63) {
 608                         reg_copy(&CONST_Z, dest);
 609                         partial_status &= ~SW_C1;       /* Round down. */
 610                         tag = TAG_Zero;
 611                 } else {
 612                         stdexp(dest);
 613                 }
 614         } else {
 615                 /* Add the magic number to the exponent. */
 616                 addexponent(dest, (3 * (1 << 13)) + EXTENDED_Ebias);
 617         }
 618 
 619         EXCEPTION(EX_Underflow);
 620         if (control_word & CW_Underflow) {
 621                 /* The underflow exception is masked. */
 622                 EXCEPTION(EX_Precision);
 623                 return tag;
 624         }
 625 
 626         return tag;
 627 
 628 }
 629 
 630 void FPU_stack_overflow(void)
 631 {
 632 
 633         if (control_word & CW_Invalid) {
 634                 /* The masked response */
 635                 top--;
 636                 FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 637         }
 638 
 639         EXCEPTION(EX_StackOver);
 640 
 641         return;
 642 
 643 }
 644 
 645 void FPU_stack_underflow(void)
 646 {
 647 
 648         if (control_word & CW_Invalid) {
 649                 /* The masked response */
 650                 FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
 651         }
 652 
 653         EXCEPTION(EX_StackUnder);
 654 
 655         return;
 656 
 657 }
 658 
 659 void FPU_stack_underflow_i(int i)
 660 {
 661 
 662         if (control_word & CW_Invalid) {
 663                 /* The masked response */
 664                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 665         }
 666 
 667         EXCEPTION(EX_StackUnder);
 668 
 669         return;
 670 
 671 }
 672 
 673 void FPU_stack_underflow_pop(int i)
 674 {
 675 
 676         if (control_word & CW_Invalid) {
 677                 /* The masked response */
 678                 FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
 679                 FPU_pop();
 680         }
 681 
 682         EXCEPTION(EX_StackUnder);
 683 
 684         return;
 685 
 686 }
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