summaryrefslogtreecommitdiff
path: root/arch/x86/math-emu/errors.c
blob: a1b0d22f697858b335165a68acd2c487eb8ad403 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
/*---------------------------------------------------------------------------+
 |  errors.c                                                                 |
 |                                                                           |
 |  The error handling functions for wm-FPU-emu                              |
 |                                                                           |
 | Copyright (C) 1992,1993,1994,1996                                         |
 |                  W. Metzenthen, 22 Parker St, Ormond, Vic 3163, Australia |
 |                  E-mail   billm@jacobi.maths.monash.edu.au                |
 |                                                                           |
 |                                                                           |
 +---------------------------------------------------------------------------*/

/*---------------------------------------------------------------------------+
 | Note:                                                                     |
 |    The file contains code which accesses user memory.                     |
 |    Emulator static data may change when user memory is accessed, due to   |
 |    other processes using the emulator while swapping is in progress.      |
 +---------------------------------------------------------------------------*/

#include <linux/signal.h>

#include <asm/uaccess.h>

#include "fpu_emu.h"
#include "fpu_system.h"
#include "exception.h"
#include "status_w.h"
#include "control_w.h"
#include "reg_constant.h"
#include "version.h"

/* */
#undef PRINT_MESSAGES
/* */


#if 0
void Un_impl(void)
{
  u_char byte1, FPU_modrm;
  unsigned long address = FPU_ORIG_EIP;

  RE_ENTRANT_CHECK_OFF;
  /* No need to check access_ok(), we have previously fetched these bytes. */
  printk("Unimplemented FPU Opcode at eip=%p : ", (void __user *) address);
  if ( FPU_CS == __USER_CS )
    {
      while ( 1 )
	{
	  FPU_get_user(byte1, (u_char __user *) address);
	  if ( (byte1 & 0xf8) == 0xd8 ) break;
	  printk("[%02x]", byte1);
	  address++;
	}
      printk("%02x ", byte1);
      FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
      
      if (FPU_modrm >= 0300)
	printk("%02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8, FPU_modrm & 7);
      else
	printk("/%d\n", (FPU_modrm >> 3) & 7);
    }
  else
    {
      printk("cs selector = %04x\n", FPU_CS);
    }

  RE_ENTRANT_CHECK_ON;

  EXCEPTION(EX_Invalid);

}
#endif  /*  0  */


/*
   Called for opcodes which are illegal and which are known to result in a
   SIGILL with a real 80486.
   */
void FPU_illegal(void)
{
  math_abort(FPU_info,SIGILL);
}



void FPU_printall(void)
{
  int i;
  static const char *tag_desc[] = { "Valid", "Zero", "ERROR", "Empty",
                              "DeNorm", "Inf", "NaN" };
  u_char byte1, FPU_modrm;
  unsigned long address = FPU_ORIG_EIP;

  RE_ENTRANT_CHECK_OFF;
  /* No need to check access_ok(), we have previously fetched these bytes. */
  printk("At %p:", (void *) address);
  if ( FPU_CS == __USER_CS )
    {
#define MAX_PRINTED_BYTES 20
      for ( i = 0; i < MAX_PRINTED_BYTES; i++ )
	{
	  FPU_get_user(byte1, (u_char __user *) address);
	  if ( (byte1 & 0xf8) == 0xd8 )
	    {
	      printk(" %02x", byte1);
	      break;
	    }
	  printk(" [%02x]", byte1);
	  address++;
	}
      if ( i == MAX_PRINTED_BYTES )
	printk(" [more..]\n");
      else
	{
	  FPU_get_user(FPU_modrm, 1 + (u_char __user *) address);
	  
	  if (FPU_modrm >= 0300)
	    printk(" %02x (%02x+%d)\n", FPU_modrm, FPU_modrm & 0xf8, FPU_modrm & 7);
	  else
	    printk(" /%d, mod=%d rm=%d\n",
		   (FPU_modrm >> 3) & 7, (FPU_modrm >> 6) & 3, FPU_modrm & 7);
	}
    }
  else
    {
      printk("%04x\n", FPU_CS);
    }

  partial_status = status_word();

#ifdef DEBUGGING
if ( partial_status & SW_Backward )    printk("SW: backward compatibility\n");
if ( partial_status & SW_C3 )          printk("SW: condition bit 3\n");
if ( partial_status & SW_C2 )          printk("SW: condition bit 2\n");
if ( partial_status & SW_C1 )          printk("SW: condition bit 1\n");
if ( partial_status & SW_C0 )          printk("SW: condition bit 0\n");
if ( partial_status & SW_Summary )     printk("SW: exception summary\n");
if ( partial_status & SW_Stack_Fault ) printk("SW: stack fault\n");
if ( partial_status & SW_Precision )   printk("SW: loss of precision\n");
if ( partial_status & SW_Underflow )   printk("SW: underflow\n");
if ( partial_status & SW_Overflow )    printk("SW: overflow\n");
if ( partial_status & SW_Zero_Div )    printk("SW: divide by zero\n");
if ( partial_status & SW_Denorm_Op )   printk("SW: denormalized operand\n");
if ( partial_status & SW_Invalid )     printk("SW: invalid operation\n");
#endif /* DEBUGGING */

  printk(" SW: b=%d st=%ld es=%d sf=%d cc=%d%d%d%d ef=%d%d%d%d%d%d\n",
	 partial_status & 0x8000 ? 1 : 0,   /* busy */
	 (partial_status & 0x3800) >> 11,   /* stack top pointer */
	 partial_status & 0x80 ? 1 : 0,     /* Error summary status */
	 partial_status & 0x40 ? 1 : 0,     /* Stack flag */
	 partial_status & SW_C3?1:0, partial_status & SW_C2?1:0, /* cc */
	 partial_status & SW_C1?1:0, partial_status & SW_C0?1:0, /* cc */
	 partial_status & SW_Precision?1:0, partial_status & SW_Underflow?1:0,
	 partial_status & SW_Overflow?1:0, partial_status & SW_Zero_Div?1:0,
	 partial_status & SW_Denorm_Op?1:0, partial_status & SW_Invalid?1:0);
  
printk(" CW: ic=%d rc=%ld%ld pc=%ld%ld iem=%d     ef=%d%d%d%d%d%d\n",
	 control_word & 0x1000 ? 1 : 0,
	 (control_word & 0x800) >> 11, (control_word & 0x400) >> 10,
	 (control_word & 0x200) >> 9, (control_word & 0x100) >> 8,
	 control_word & 0x80 ? 1 : 0,
	 control_word & SW_Precision?1:0, control_word & SW_Underflow?1:0,
	 control_word & SW_Overflow?1:0, control_word & SW_Zero_Div?1:0,
	 control_word & SW_Denorm_Op?1:0, control_word & SW_Invalid?1:0);

  for ( i = 0; i < 8; i++ )
    {
      FPU_REG *r = &st(i);
      u_char tagi = FPU_gettagi(i);
      switch (tagi)
	{
	case TAG_Empty:
	  continue;
	  break;
	case TAG_Zero:
	case TAG_Special:
	  tagi = FPU_Special(r);
	case TAG_Valid:
	  printk("st(%d)  %c .%04lx %04lx %04lx %04lx e%+-6d ", i,
		 getsign(r) ? '-' : '+',
		 (long)(r->sigh >> 16),
		 (long)(r->sigh & 0xFFFF),
		 (long)(r->sigl >> 16),
		 (long)(r->sigl & 0xFFFF),
		 exponent(r) - EXP_BIAS + 1);
	  break;
	default:
	  printk("Whoops! Error in errors.c: tag%d is %d ", i, tagi);
	  continue;
	  break;
	}
      printk("%s\n", tag_desc[(int) (unsigned) tagi]);
    }

  RE_ENTRANT_CHECK_ON;

}

static struct {
  int type;
  const char *name;
} exception_names[] = {
  { EX_StackOver, "stack overflow" },
  { EX_StackUnder, "stack underflow" },
  { EX_Precision, "loss of precision" },
  { EX_Underflow, "underflow" },
  { EX_Overflow, "overflow" },
  { EX_ZeroDiv, "divide by zero" },
  { EX_Denormal, "denormalized operand" },
  { EX_Invalid, "invalid operation" },
  { EX_INTERNAL, "INTERNAL BUG in "FPU_VERSION },
  { 0, NULL }
};

/*
 EX_INTERNAL is always given with a code which indicates where the
 error was detected.

 Internal error types:
       0x14   in fpu_etc.c
       0x1nn  in a *.c file:
              0x101  in reg_add_sub.c
              0x102  in reg_mul.c
              0x104  in poly_atan.c
              0x105  in reg_mul.c
              0x107  in fpu_trig.c
	      0x108  in reg_compare.c
	      0x109  in reg_compare.c
	      0x110  in reg_add_sub.c
	      0x111  in fpe_entry.c
	      0x112  in fpu_trig.c
	      0x113  in errors.c
	      0x115  in fpu_trig.c
	      0x116  in fpu_trig.c
	      0x117  in fpu_trig.c
	      0x118  in fpu_trig.c
	      0x119  in fpu_trig.c
	      0x120  in poly_atan.c
	      0x121  in reg_compare.c
	      0x122  in reg_compare.c
	      0x123  in reg_compare.c
	      0x125  in fpu_trig.c
	      0x126  in fpu_entry.c
	      0x127  in poly_2xm1.c
	      0x128  in fpu_entry.c
	      0x129  in fpu_entry.c
	      0x130  in get_address.c
	      0x131  in get_address.c
	      0x132  in get_address.c
	      0x133  in get_address.c
	      0x140  in load_store.c
	      0x141  in load_store.c
              0x150  in poly_sin.c
              0x151  in poly_sin.c
	      0x160  in reg_ld_str.c
	      0x161  in reg_ld_str.c
	      0x162  in reg_ld_str.c
	      0x163  in reg_ld_str.c
	      0x164  in reg_ld_str.c
	      0x170  in fpu_tags.c
	      0x171  in fpu_tags.c
	      0x172  in fpu_tags.c
	      0x180  in reg_convert.c
       0x2nn  in an *.S file:
              0x201  in reg_u_add.S
              0x202  in reg_u_div.S
              0x203  in reg_u_div.S
              0x204  in reg_u_div.S
              0x205  in reg_u_mul.S
              0x206  in reg_u_sub.S
              0x207  in wm_sqrt.S
	      0x208  in reg_div.S
              0x209  in reg_u_sub.S
              0x210  in reg_u_sub.S
              0x211  in reg_u_sub.S
              0x212  in reg_u_sub.S
	      0x213  in wm_sqrt.S
	      0x214  in wm_sqrt.S
	      0x215  in wm_sqrt.S
	      0x220  in reg_norm.S
	      0x221  in reg_norm.S
	      0x230  in reg_round.S
	      0x231  in reg_round.S
	      0x232  in reg_round.S
	      0x233  in reg_round.S
	      0x234  in reg_round.S
	      0x235  in reg_round.S
	      0x236  in reg_round.S
	      0x240  in div_Xsig.S
	      0x241  in div_Xsig.S
	      0x242  in div_Xsig.S
 */

asmlinkage void FPU_exception(int n)
{
  int i, int_type;

  int_type = 0;         /* Needed only to stop compiler warnings */
  if ( n & EX_INTERNAL )
    {
      int_type = n - EX_INTERNAL;
      n = EX_INTERNAL;
      /* Set lots of exception bits! */
      partial_status |= (SW_Exc_Mask | SW_Summary | SW_Backward);
    }
  else
    {
      /* Extract only the bits which we use to set the status word */
      n &= (SW_Exc_Mask);
      /* Set the corresponding exception bit */
      partial_status |= n;
      /* Set summary bits iff exception isn't masked */
      if ( partial_status & ~control_word & CW_Exceptions )
	partial_status |= (SW_Summary | SW_Backward);
      if ( n & (SW_Stack_Fault | EX_Precision) )
	{
	  if ( !(n & SW_C1) )
	    /* This bit distinguishes over- from underflow for a stack fault,
	       and roundup from round-down for precision loss. */
	    partial_status &= ~SW_C1;
	}
    }

  RE_ENTRANT_CHECK_OFF;
  if ( (~control_word & n & CW_Exceptions) || (n == EX_INTERNAL) )
    {
#ifdef PRINT_MESSAGES
      /* My message from the sponsor */
      printk(FPU_VERSION" "__DATE__" (C) W. Metzenthen.\n");
#endif /* PRINT_MESSAGES */
      
      /* Get a name string for error reporting */
      for (i=0; exception_names[i].type; i++)
	if ( (exception_names[i].type & n) == exception_names[i].type )
	  break;
      
      if (exception_names[i].type)
	{
#ifdef PRINT_MESSAGES
	  printk("FP Exception: %s!\n", exception_names[i].name);
#endif /* PRINT_MESSAGES */
	}
      else
	printk("FPU emulator: Unknown Exception: 0x%04x!\n", n);
      
      if ( n == EX_INTERNAL )
	{
	  printk("FPU emulator: Internal error type 0x%04x\n", int_type);
	  FPU_printall();
	}
#ifdef PRINT_MESSAGES
      else
	FPU_printall();
#endif /* PRINT_MESSAGES */

      /*
       * The 80486 generates an interrupt on the next non-control FPU
       * instruction. So we need some means of flagging it.
       * We use the ES (Error Summary) bit for this.
       */
    }
  RE_ENTRANT_CHECK_ON;

#ifdef __DEBUG__
  math_abort(FPU_info,SIGFPE);
#endif /* __DEBUG__ */

}


/* Real operation attempted on a NaN. */
/* Returns < 0 if the exception is unmasked */
int real_1op_NaN(FPU_REG *a)
{
  int signalling, isNaN;

  isNaN = (exponent(a) == EXP_OVER) && (a->sigh & 0x80000000);

  /* The default result for the case of two "equal" NaNs (signs may
     differ) is chosen to reproduce 80486 behaviour */
  signalling = isNaN && !(a->sigh & 0x40000000);

  if ( !signalling )
    {
      if ( !isNaN )  /* pseudo-NaN, or other unsupported? */
	{
	  if ( control_word & CW_Invalid )
	    {
	      /* Masked response */
	      reg_copy(&CONST_QNaN, a);
	    }
	  EXCEPTION(EX_Invalid);
	  return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
	}
      return TAG_Special;
    }

  if ( control_word & CW_Invalid )
    {
      /* The masked response */
      if ( !(a->sigh & 0x80000000) )  /* pseudo-NaN ? */
	{
	  reg_copy(&CONST_QNaN, a);
	}
      /* ensure a Quiet NaN */
      a->sigh |= 0x40000000;
    }

  EXCEPTION(EX_Invalid);

  return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
}


/* Real operation attempted on two operands, one a NaN. */
/* Returns < 0 if the exception is unmasked */
int real_2op_NaN(FPU_REG const *b, u_char tagb,
		 int deststnr,
		 FPU_REG const *defaultNaN)
{
  FPU_REG *dest = &st(deststnr);
  FPU_REG const *a = dest;
  u_char taga = FPU_gettagi(deststnr);
  FPU_REG const *x;
  int signalling, unsupported;

  if ( taga == TAG_Special )
    taga = FPU_Special(a);
  if ( tagb == TAG_Special )
    tagb = FPU_Special(b);

  /* TW_NaN is also used for unsupported data types. */
  unsupported = ((taga == TW_NaN)
		 && !((exponent(a) == EXP_OVER) && (a->sigh & 0x80000000)))
    || ((tagb == TW_NaN)
	&& !((exponent(b) == EXP_OVER) && (b->sigh & 0x80000000)));
  if ( unsupported )
    {
      if ( control_word & CW_Invalid )
	{
	  /* Masked response */
	  FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
	}
      EXCEPTION(EX_Invalid);
      return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
    }

  if (taga == TW_NaN)
    {
      x = a;
      if (tagb == TW_NaN)
	{
	  signalling = !(a->sigh & b->sigh & 0x40000000);
	  if ( significand(b) > significand(a) )
	    x = b;
	  else if ( significand(b) == significand(a) )
	    {
	      /* The default result for the case of two "equal" NaNs (signs may
		 differ) is chosen to reproduce 80486 behaviour */
	      x = defaultNaN;
	    }
	}
      else
	{
	  /* return the quiet version of the NaN in a */
	  signalling = !(a->sigh & 0x40000000);
	}
    }
  else
#ifdef PARANOID
    if (tagb == TW_NaN)
#endif /* PARANOID */
    {
      signalling = !(b->sigh & 0x40000000);
      x = b;
    }
#ifdef PARANOID
  else
    {
      signalling = 0;
      EXCEPTION(EX_INTERNAL|0x113);
      x = &CONST_QNaN;
    }
#endif /* PARANOID */

  if ( (!signalling) || (control_word & CW_Invalid) )
    {
      if ( ! x )
	x = b;

      if ( !(x->sigh & 0x80000000) )  /* pseudo-NaN ? */
	x = &CONST_QNaN;

      FPU_copy_to_regi(x, TAG_Special, deststnr);

      if ( !signalling )
	return TAG_Special;

      /* ensure a Quiet NaN */
      dest->sigh |= 0x40000000;
    }

  EXCEPTION(EX_Invalid);

  return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Special;
}


/* Invalid arith operation on Valid registers */
/* Returns < 0 if the exception is unmasked */
asmlinkage int arith_invalid(int deststnr)
{

  EXCEPTION(EX_Invalid);
  
  if ( control_word & CW_Invalid )
    {
      /* The masked response */
      FPU_copy_to_regi(&CONST_QNaN, TAG_Special, deststnr);
    }
  
  return (!(control_word & CW_Invalid) ? FPU_Exception : 0) | TAG_Valid;

}


/* Divide a finite number by zero */
asmlinkage int FPU_divide_by_zero(int deststnr, u_char sign)
{
  FPU_REG *dest = &st(deststnr);
  int tag = TAG_Valid;

  if ( control_word & CW_ZeroDiv )
    {
      /* The masked response */
      FPU_copy_to_regi(&CONST_INF, TAG_Special, deststnr);
      setsign(dest, sign);
      tag = TAG_Special;
    }
 
  EXCEPTION(EX_ZeroDiv);

  return (!(control_word & CW_ZeroDiv) ? FPU_Exception : 0) | tag;

}


/* This may be called often, so keep it lean */
int set_precision_flag(int flags)
{
  if ( control_word & CW_Precision )
    {
      partial_status &= ~(SW_C1 & flags);
      partial_status |= flags;   /* The masked response */
      return 0;
    }
  else
    {
      EXCEPTION(flags);
      return 1;
    }
}


/* This may be called often, so keep it lean */
asmlinkage void set_precision_flag_up(void)
{
  if ( control_word & CW_Precision )
    partial_status |= (SW_Precision | SW_C1);   /* The masked response */
  else
    EXCEPTION(EX_Precision | SW_C1);
}


/* This may be called often, so keep it lean */
asmlinkage void set_precision_flag_down(void)
{
  if ( control_word & CW_Precision )
    {   /* The masked response */
      partial_status &= ~SW_C1;
      partial_status |= SW_Precision;
    }
  else
    EXCEPTION(EX_Precision);
}


asmlinkage int denormal_operand(void)
{
  if ( control_word & CW_Denormal )
    {   /* The masked response */
      partial_status |= SW_Denorm_Op;
      return TAG_Special;
    }
  else
    {
      EXCEPTION(EX_Denormal);
      return TAG_Special | FPU_Exception;
    }
}


asmlinkage int arith_overflow(FPU_REG *dest)
{
  int tag = TAG_Valid;

  if ( control_word & CW_Overflow )
    {
      /* The masked response */
/* ###### The response here depends upon the rounding mode */
      reg_copy(&CONST_INF, dest);
      tag = TAG_Special;
    }
  else
    {
      /* Subtract the magic number from the exponent */
      addexponent(dest, (-3 * (1 << 13)));
    }

  EXCEPTION(EX_Overflow);
  if ( control_word & CW_Overflow )
    {
      /* The overflow exception is masked. */
      /* By definition, precision is lost.
	 The roundup bit (C1) is also set because we have
	 "rounded" upwards to Infinity. */
      EXCEPTION(EX_Precision | SW_C1);
      return tag;
    }

  return tag;

}


asmlinkage int arith_underflow(FPU_REG *dest)
{
  int tag = TAG_Valid;

  if ( control_word & CW_Underflow )
    {
      /* The masked response */
      if ( exponent16(dest) <= EXP_UNDER - 63 )
	{
	  reg_copy(&CONST_Z, dest);
	  partial_status &= ~SW_C1;       /* Round down. */
	  tag = TAG_Zero;
	}
      else
	{
	  stdexp(dest);
	}
    }
  else
    {
      /* Add the magic number to the exponent. */
      addexponent(dest, (3 * (1 << 13)) + EXTENDED_Ebias);
    }

  EXCEPTION(EX_Underflow);
  if ( control_word & CW_Underflow )
    {
      /* The underflow exception is masked. */
      EXCEPTION(EX_Precision);
      return tag;
    }

  return tag;

}


void FPU_stack_overflow(void)
{

 if ( control_word & CW_Invalid )
    {
      /* The masked response */
      top--;
      FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
    }

  EXCEPTION(EX_StackOver);

  return;

}


void FPU_stack_underflow(void)
{

 if ( control_word & CW_Invalid )
    {
      /* The masked response */
      FPU_copy_to_reg0(&CONST_QNaN, TAG_Special);
    }

  EXCEPTION(EX_StackUnder);

  return;

}


void FPU_stack_underflow_i(int i)
{

 if ( control_word & CW_Invalid )
    {
      /* The masked response */
      FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
    }

  EXCEPTION(EX_StackUnder);

  return;

}


void FPU_stack_underflow_pop(int i)
{

 if ( control_word & CW_Invalid )
    {
      /* The masked response */
      FPU_copy_to_regi(&CONST_QNaN, TAG_Special, i);
      FPU_pop();
    }

  EXCEPTION(EX_StackUnder);

  return;

}