summaryrefslogtreecommitdiff
path: root/trionan.c
blob: 5248eaf64466dd72d571d0bf156d712738723ce9 (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
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
/*************************************************************************
 *
 * $Id: trionan.c,v 1.14 2003/10/15 08:17:58 veillard Exp $
 *
 * Copyright (C) 2001 Bjorn Reese <breese@users.sourceforge.net>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
 * MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE AUTHORS AND
 * CONTRIBUTORS ACCEPT NO RESPONSIBILITY IN ANY CONCEIVABLE MANNER.
 *
 ************************************************************************
 *
 * Functions to handle special quantities in floating-point numbers
 * (that is, NaNs and infinity). They provide the capability to detect
 * and fabricate special quantities.
 *
 * Although written to be as portable as possible, it can never be
 * guaranteed to work on all platforms, as not all hardware supports
 * special quantities.
 *
 * The approach used here (approximately) is to:
 *
 *   1. Use C99 functionality when available.
 *   2. Use IEEE 754 bit-patterns if possible.
 *   3. Use platform-specific techniques.
 *
 ************************************************************************/

/*
 * TODO:
 *  o Put all the magic into trio_fpclassify_and_signbit(), and use this from
 *    trio_isnan() etc.
 */

/*************************************************************************
 * Include files
 */
#include "triodef.h"
#include "trionan.h"

#include <math.h>
#include <string.h>
#include <limits.h>
#include <float.h>
#if defined(TRIO_PLATFORM_UNIX)
# include <signal.h>
#endif
#if defined(TRIO_COMPILER_DECC)
#  if defined(__linux__)
#   include <cpml.h>
#  else
#   include <fp_class.h>
#  endif
#endif
#include <assert.h>

#if defined(TRIO_DOCUMENTATION)
# include "doc/doc_nan.h"
#endif
/** @addtogroup SpecialQuantities
    @{
*/

/*************************************************************************
 * Definitions
 */

#define TRIO_TRUE (1 == 1)
#define TRIO_FALSE (0 == 1)

/*
 * We must enable IEEE floating-point on Alpha
 */
#if defined(__alpha) && !defined(_IEEE_FP)
# if defined(TRIO_COMPILER_DECC)
#  if defined(TRIO_PLATFORM_VMS)
#   error "Must be compiled with option /IEEE_MODE=UNDERFLOW_TO_ZERO/FLOAT=IEEE"
#  else
#   if !defined(_CFE)
#    error "Must be compiled with option -ieee"
#   endif
#  endif
# elif defined(TRIO_COMPILER_GCC) && (defined(__osf__) || defined(__linux__))
#  error "Must be compiled with option -mieee"
# endif
#endif /* __alpha && ! _IEEE_FP */

/*
 * In ANSI/IEEE 754-1985 64-bits double format numbers have the
 * following properties (amoungst others)
 *
 *   o FLT_RADIX == 2: binary encoding
 *   o DBL_MAX_EXP == 1024: 11 bits exponent, where one bit is used
 *     to indicate special numbers (e.g. NaN and Infinity), so the
 *     maximum exponent is 10 bits wide (2^10 == 1024).
 *   o DBL_MANT_DIG == 53: The mantissa is 52 bits wide, but because
 *     numbers are normalized the initial binary 1 is represented
 *     implicitly (the so-called "hidden bit"), which leaves us with
 *     the ability to represent 53 bits wide mantissa.
 */
#if (FLT_RADIX == 2) && (DBL_MAX_EXP == 1024) && (DBL_MANT_DIG == 53)
# define USE_IEEE_754
#endif


/*************************************************************************
 * Constants
 */

static TRIO_CONST char rcsid[] = "@(#)$Id: trionan.c,v 1.14 2003/10/15 08:17:58 veillard Exp $";

#if defined(USE_IEEE_754)

/*
 * Endian-agnostic indexing macro.
 *
 * The value of internalEndianMagic, when converted into a 64-bit
 * integer, becomes 0x0706050403020100 (we could have used a 64-bit
 * integer value instead of a double, but not all platforms supports
 * that type). The value is automatically encoded with the correct
 * endianess by the compiler, which means that we can support any
 * kind of endianess. The individual bytes are then used as an index
 * for the IEEE 754 bit-patterns and masks.
 */
#define TRIO_DOUBLE_INDEX(x) (((unsigned char *)&internalEndianMagic)[7-(x)])

static TRIO_CONST double internalEndianMagic = 7.949928895127363e-275;

/* Mask for the exponent */
static TRIO_CONST unsigned char ieee_754_exponent_mask[] = {
  0x7F, 0xF0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

/* Mask for the mantissa */
static TRIO_CONST unsigned char ieee_754_mantissa_mask[] = {
  0x00, 0x0F, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF
};

/* Mask for the sign bit */
static TRIO_CONST unsigned char ieee_754_sign_mask[] = {
  0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

/* Bit-pattern for negative zero */
static TRIO_CONST unsigned char ieee_754_negzero_array[] = {
  0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

/* Bit-pattern for infinity */
static TRIO_CONST unsigned char ieee_754_infinity_array[] = {
  0x7F, 0xF0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};

/* Bit-pattern for quiet NaN */
static TRIO_CONST unsigned char ieee_754_qnan_array[] = {
  0x7F, 0xF8, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
};


/*************************************************************************
 * Functions
 */

/*
 * trio_make_double
 */
TRIO_PRIVATE double
trio_make_double
TRIO_ARGS1((values),
	   TRIO_CONST unsigned char *values)
{
  TRIO_VOLATILE double result;
  int i;

  for (i = 0; i < (int)sizeof(double); i++) {
    ((TRIO_VOLATILE unsigned char *)&result)[TRIO_DOUBLE_INDEX(i)] = values[i];
  }
  return result;
}

/*
 * trio_is_special_quantity
 */
TRIO_PRIVATE int
trio_is_special_quantity
TRIO_ARGS2((number, has_mantissa),
	   double number,
	   int *has_mantissa)
{
  unsigned int i;
  unsigned char current;
  int is_special_quantity = TRIO_TRUE;

  *has_mantissa = 0;

  for (i = 0; i < (unsigned int)sizeof(double); i++) {
    current = ((unsigned char *)&number)[TRIO_DOUBLE_INDEX(i)];
    is_special_quantity
      &= ((current & ieee_754_exponent_mask[i]) == ieee_754_exponent_mask[i]);
    *has_mantissa |= (current & ieee_754_mantissa_mask[i]);
  }
  return is_special_quantity;
}

/*
 * trio_is_negative
 */
TRIO_PRIVATE int
trio_is_negative
TRIO_ARGS1((number),
	   double number)
{
  unsigned int i;
  int is_negative = TRIO_FALSE;

  for (i = 0; i < (unsigned int)sizeof(double); i++) {
    is_negative |= (((unsigned char *)&number)[TRIO_DOUBLE_INDEX(i)]
		    & ieee_754_sign_mask[i]);
  }
  return is_negative;
}

#endif /* USE_IEEE_754 */


/**
   Generate negative zero.

   @return Floating-point representation of negative zero.
*/
TRIO_PUBLIC double
trio_nzero(TRIO_NOARGS)
{
#if defined(USE_IEEE_754)
  return trio_make_double(ieee_754_negzero_array);
#else
  TRIO_VOLATILE double zero = 0.0;

  return -zero;
#endif
}

/**
   Generate positive infinity.

   @return Floating-point representation of positive infinity.
*/
TRIO_PUBLIC double
trio_pinf(TRIO_NOARGS)
{
  /* Cache the result */
  static double result = 0.0;

  if (result == 0.0) {
    
#if defined(INFINITY) && defined(__STDC_IEC_559__)
    result = (double)INFINITY;

#elif defined(USE_IEEE_754)
    result = trio_make_double(ieee_754_infinity_array);

#else
    /*
     * If HUGE_VAL is different from DBL_MAX, then HUGE_VAL is used
     * as infinity. Otherwise we have to resort to an overflow
     * operation to generate infinity.
     */
# if defined(TRIO_PLATFORM_UNIX)
    void (*signal_handler)(int) = signal(SIGFPE, SIG_IGN);
# endif

    result = HUGE_VAL;
    if (HUGE_VAL == DBL_MAX) {
      /* Force overflow */
      result += HUGE_VAL;
    }
    
# if defined(TRIO_PLATFORM_UNIX)
    signal(SIGFPE, signal_handler);
# endif

#endif
  }
  return result;
}

/**
   Generate negative infinity.

   @return Floating-point value of negative infinity.
*/
TRIO_PUBLIC double
trio_ninf(TRIO_NOARGS)
{
  static double result = 0.0;

  if (result == 0.0) {
    /*
     * Negative infinity is calculated by negating positive infinity,
     * which can be done because it is legal to do calculations on
     * infinity (for example,  1 / infinity == 0).
     */
    result = -trio_pinf();
  }
  return result;
}

/**
   Generate NaN.

   @return Floating-point representation of NaN.
*/
TRIO_PUBLIC double
trio_nan(TRIO_NOARGS)
{
  /* Cache the result */
  static double result = 0.0;

  if (result == 0.0) {
    
#if defined(TRIO_COMPILER_SUPPORTS_C99)
    result = nan("");

#elif defined(NAN) && defined(__STDC_IEC_559__)
    result = (double)NAN;
  
#elif defined(USE_IEEE_754)
    result = trio_make_double(ieee_754_qnan_array);

#else
    /*
     * There are several ways to generate NaN. The one used here is
     * to divide infinity by infinity. I would have preferred to add
     * negative infinity to positive infinity, but that yields wrong
     * result (infinity) on FreeBSD.
     *
     * This may fail if the hardware does not support NaN, or if
     * the Invalid Operation floating-point exception is unmasked.
     */
# if defined(TRIO_PLATFORM_UNIX)
    void (*signal_handler)(int) = signal(SIGFPE, SIG_IGN);
# endif
    
    result = trio_pinf() / trio_pinf();
    
# if defined(TRIO_PLATFORM_UNIX)
    signal(SIGFPE, signal_handler);
# endif
    
#endif
  }
  return result;
}

/**
   Check for NaN.

   @param number An arbitrary floating-point number.
   @return Boolean value indicating whether or not the number is a NaN.
*/
TRIO_PUBLIC int
trio_isnan
TRIO_ARGS1((number),
	   double number)
{
#if (defined(TRIO_COMPILER_SUPPORTS_C99) && defined(isnan)) \
 || defined(TRIO_COMPILER_SUPPORTS_UNIX95)
  /*
   * C99 defines isnan() as a macro. UNIX95 defines isnan() as a
   * function. This function was already present in XPG4, but this
   * is a bit tricky to detect with compiler defines, so we choose
   * the conservative approach and only use it for UNIX95.
   */
  return isnan(number);
  
#elif defined(TRIO_COMPILER_MSVC) || defined(TRIO_COMPILER_BCB)
  /*
   * Microsoft Visual C++ and Borland C++ Builder have an _isnan()
   * function.
   */
  return _isnan(number) ? TRIO_TRUE : TRIO_FALSE;

#elif defined(USE_IEEE_754)
  /*
   * Examine IEEE 754 bit-pattern. A NaN must have a special exponent
   * pattern, and a non-empty mantissa.
   */
  int has_mantissa;
  int is_special_quantity;

  is_special_quantity = trio_is_special_quantity(number, &has_mantissa);
  
  return (is_special_quantity && has_mantissa);
  
#else
  /*
   * Fallback solution
   */
  int status;
  double integral, fraction;
  
# if defined(TRIO_PLATFORM_UNIX)
  void (*signal_handler)(int) = signal(SIGFPE, SIG_IGN);
# endif
  
  status = (/*
	     * NaN is the only number which does not compare to itself
	     */
	    ((TRIO_VOLATILE double)number != (TRIO_VOLATILE double)number) ||
	    /*
	     * Fallback solution if NaN compares to NaN
	     */
	    ((number != 0.0) &&
	     (fraction = modf(number, &integral),
	      integral == fraction)));
  
# if defined(TRIO_PLATFORM_UNIX)
  signal(SIGFPE, signal_handler);
# endif
  
  return status;
  
#endif
}

/**
   Check for infinity.

   @param number An arbitrary floating-point number.
   @return 1 if positive infinity, -1 if negative infinity, 0 otherwise.
*/
TRIO_PUBLIC int
trio_isinf
TRIO_ARGS1((number),
	   double number)
{
#if defined(TRIO_COMPILER_DECC) && !defined(__linux__)
  /*
   * DECC has an isinf() macro, but it works differently than that
   * of C99, so we use the fp_class() function instead.
   */
  return ((fp_class(number) == FP_POS_INF)
	  ? 1
	  : ((fp_class(number) == FP_NEG_INF) ? -1 : 0));

#elif defined(isinf)
  /*
   * C99 defines isinf() as a macro.
   */
  return isinf(number)
    ? ((number > 0.0) ? 1 : -1)
    : 0;
  
#elif defined(TRIO_COMPILER_MSVC) || defined(TRIO_COMPILER_BCB)
  /*
   * Microsoft Visual C++ and Borland C++ Builder have an _fpclass()
   * function that can be used to detect infinity.
   */
  return ((_fpclass(number) == _FPCLASS_PINF)
	  ? 1
	  : ((_fpclass(number) == _FPCLASS_NINF) ? -1 : 0));

#elif defined(USE_IEEE_754)
  /*
   * Examine IEEE 754 bit-pattern. Infinity must have a special exponent
   * pattern, and an empty mantissa.
   */
  int has_mantissa;
  int is_special_quantity;

  is_special_quantity = trio_is_special_quantity(number, &has_mantissa);
  
  return (is_special_quantity && !has_mantissa)
    ? ((number < 0.0) ? -1 : 1)
    : 0;

#else
  /*
   * Fallback solution.
   */
  int status;
  
# if defined(TRIO_PLATFORM_UNIX)
  void (*signal_handler)(int) = signal(SIGFPE, SIG_IGN);
# endif
  
  double infinity = trio_pinf();
  
  status = ((number == infinity)
	    ? 1
	    : ((number == -infinity) ? -1 : 0));
  
# if defined(TRIO_PLATFORM_UNIX)
  signal(SIGFPE, signal_handler);
# endif
  
  return status;
  
#endif
}

#if 0
	/* Temporary fix - this routine is not used anywhere */
/**
   Check for finity.

   @param number An arbitrary floating-point number.
   @return Boolean value indicating whether or not the number is a finite.
*/
TRIO_PUBLIC int
trio_isfinite
TRIO_ARGS1((number),
	   double number)
{
#if defined(TRIO_COMPILER_SUPPORTS_C99) && defined(isfinite)
  /*
   * C99 defines isfinite() as a macro.
   */
  return isfinite(number);
  
#elif defined(TRIO_COMPILER_MSVC) || defined(TRIO_COMPILER_BCB)
  /*
   * Microsoft Visual C++ and Borland C++ Builder use _finite().
   */
  return _finite(number);

#elif defined(USE_IEEE_754)
  /*
   * Examine IEEE 754 bit-pattern. For finity we do not care about the
   * mantissa.
   */
  int dummy;

  return (! trio_is_special_quantity(number, &dummy));

#else
  /*
   * Fallback solution.
   */
  return ((trio_isinf(number) == 0) && (trio_isnan(number) == 0));
  
#endif
}

#endif

/*
 * The sign of NaN is always false
 */
TRIO_PUBLIC int
trio_fpclassify_and_signbit
TRIO_ARGS2((number, is_negative),
	   double number,
	   int *is_negative)
{
#if defined(fpclassify) && defined(signbit)
  /*
   * C99 defines fpclassify() and signbit() as a macros
   */
  *is_negative = signbit(number);
  switch (fpclassify(number)) {
  case FP_NAN:
    return TRIO_FP_NAN;
  case FP_INFINITE:
    return TRIO_FP_INFINITE;
  case FP_SUBNORMAL:
    return TRIO_FP_SUBNORMAL;
  case FP_ZERO:
    return TRIO_FP_ZERO;
  default:
    return TRIO_FP_NORMAL;
  }

#else
# if defined(TRIO_COMPILER_DECC)
  /*
   * DECC has an fp_class() function.
   */
#  define TRIO_FPCLASSIFY(n) fp_class(n)
#  define TRIO_QUIET_NAN FP_QNAN
#  define TRIO_SIGNALLING_NAN FP_SNAN
#  define TRIO_POSITIVE_INFINITY FP_POS_INF
#  define TRIO_NEGATIVE_INFINITY FP_NEG_INF
#  define TRIO_POSITIVE_SUBNORMAL FP_POS_DENORM
#  define TRIO_NEGATIVE_SUBNORMAL FP_NEG_DENORM
#  define TRIO_POSITIVE_ZERO FP_POS_ZERO
#  define TRIO_NEGATIVE_ZERO FP_NEG_ZERO
#  define TRIO_POSITIVE_NORMAL FP_POS_NORM
#  define TRIO_NEGATIVE_NORMAL FP_NEG_NORM
  
# elif defined(TRIO_COMPILER_MSVC) || defined(TRIO_COMPILER_BCB)
  /*
   * Microsoft Visual C++ and Borland C++ Builder have an _fpclass()
   * function.
   */
#  define TRIO_FPCLASSIFY(n) _fpclass(n)
#  define TRIO_QUIET_NAN _FPCLASS_QNAN
#  define TRIO_SIGNALLING_NAN _FPCLASS_SNAN
#  define TRIO_POSITIVE_INFINITY _FPCLASS_PINF
#  define TRIO_NEGATIVE_INFINITY _FPCLASS_NINF
#  define TRIO_POSITIVE_SUBNORMAL _FPCLASS_PD
#  define TRIO_NEGATIVE_SUBNORMAL _FPCLASS_ND
#  define TRIO_POSITIVE_ZERO _FPCLASS_PZ
#  define TRIO_NEGATIVE_ZERO _FPCLASS_NZ
#  define TRIO_POSITIVE_NORMAL _FPCLASS_PN
#  define TRIO_NEGATIVE_NORMAL _FPCLASS_NN
  
# elif defined(FP_PLUS_NORM)
  /*
   * HP-UX 9.x and 10.x have an fpclassify() function, that is different
   * from the C99 fpclassify() macro supported on HP-UX 11.x.
   *
   * AIX has class() for C, and _class() for C++, which returns the
   * same values as the HP-UX fpclassify() function.
   */
#  if defined(TRIO_PLATFORM_AIX)
#   if defined(__cplusplus)
#    define TRIO_FPCLASSIFY(n) _class(n)
#   else
#    define TRIO_FPCLASSIFY(n) class(n)
#   endif
#  else
#   define TRIO_FPCLASSIFY(n) fpclassify(n)
#  endif
#  define TRIO_QUIET_NAN FP_QNAN
#  define TRIO_SIGNALLING_NAN FP_SNAN
#  define TRIO_POSITIVE_INFINITY FP_PLUS_INF
#  define TRIO_NEGATIVE_INFINITY FP_MINUS_INF
#  define TRIO_POSITIVE_SUBNORMAL FP_PLUS_DENORM
#  define TRIO_NEGATIVE_SUBNORMAL FP_MINUS_DENORM
#  define TRIO_POSITIVE_ZERO FP_PLUS_ZERO
#  define TRIO_NEGATIVE_ZERO FP_MINUS_ZERO
#  define TRIO_POSITIVE_NORMAL FP_PLUS_NORM
#  define TRIO_NEGATIVE_NORMAL FP_MINUS_NORM
# endif

# if defined(TRIO_FPCLASSIFY)
  switch (TRIO_FPCLASSIFY(number)) {
  case TRIO_QUIET_NAN:
  case TRIO_SIGNALLING_NAN:
    *is_negative = TRIO_FALSE; /* NaN has no sign */
    return TRIO_FP_NAN;
  case TRIO_POSITIVE_INFINITY:
    *is_negative = TRIO_FALSE;
    return TRIO_FP_INFINITE;
  case TRIO_NEGATIVE_INFINITY:
    *is_negative = TRIO_TRUE;
    return TRIO_FP_INFINITE;
  case TRIO_POSITIVE_SUBNORMAL:
    *is_negative = TRIO_FALSE;
    return TRIO_FP_SUBNORMAL;
  case TRIO_NEGATIVE_SUBNORMAL:
    *is_negative = TRIO_TRUE;
    return TRIO_FP_SUBNORMAL;
  case TRIO_POSITIVE_ZERO:
    *is_negative = TRIO_FALSE;
    return TRIO_FP_ZERO;
  case TRIO_NEGATIVE_ZERO:
    *is_negative = TRIO_TRUE;
    return TRIO_FP_ZERO;
  case TRIO_POSITIVE_NORMAL:
    *is_negative = TRIO_FALSE;
    return TRIO_FP_NORMAL;
  case TRIO_NEGATIVE_NORMAL:
    *is_negative = TRIO_TRUE;
    return TRIO_FP_NORMAL;
  default:
    /* Just in case... */
    *is_negative = (number < 0.0);
    return TRIO_FP_NORMAL;
  }
  
# else
  /*
   * Fallback solution.
   */
  int rc;
  
  if (number == 0.0) {
    /*
     * In IEEE 754 the sign of zero is ignored in comparisons, so we
     * have to handle this as a special case by examining the sign bit
     * directly.
     */
#  if defined(USE_IEEE_754)
    *is_negative = trio_is_negative(number);
#  else
    *is_negative = TRIO_FALSE; /* FIXME */
#  endif
    return TRIO_FP_ZERO;
  }
  if (trio_isnan(number)) {
    *is_negative = TRIO_FALSE;
    return TRIO_FP_NAN;
  }
  if ((rc = trio_isinf(number))) {
    *is_negative = (rc == -1);
    return TRIO_FP_INFINITE;
  }
  if ((number > 0.0) && (number < DBL_MIN)) {
    *is_negative = TRIO_FALSE;
    return TRIO_FP_SUBNORMAL;
  }
  if ((number < 0.0) && (number > -DBL_MIN)) {
    *is_negative = TRIO_TRUE;
    return TRIO_FP_SUBNORMAL;
  }
  *is_negative = (number < 0.0);
  return TRIO_FP_NORMAL;
  
# endif
#endif
}

/**
   Examine the sign of a number.

   @param number An arbitrary floating-point number.
   @return Boolean value indicating whether or not the number has the
   sign bit set (i.e. is negative).
*/
TRIO_PUBLIC int
trio_signbit
TRIO_ARGS1((number),
	   double number)
{
  int is_negative;
  
  (void)trio_fpclassify_and_signbit(number, &is_negative);
  return is_negative;
}

#if 0
	/* Temporary fix - this routine is not used in libxml */
/**
   Examine the class of a number.

   @param number An arbitrary floating-point number.
   @return Enumerable value indicating the class of @p number
*/
TRIO_PUBLIC int
trio_fpclassify
TRIO_ARGS1((number),
	   double number)
{
  int dummy;
  
  return trio_fpclassify_and_signbit(number, &dummy);
}

#endif

/** @} SpecialQuantities */

/*************************************************************************
 * For test purposes.
 *
 * Add the following compiler option to include this test code.
 *
 *  Unix : -DSTANDALONE
 *  VMS  : /DEFINE=(STANDALONE)
 */
#if defined(STANDALONE)
# include <stdio.h>

static TRIO_CONST char *
getClassification
TRIO_ARGS1((type),
	   int type)
{
  switch (type) {
  case TRIO_FP_INFINITE:
    return "FP_INFINITE";
  case TRIO_FP_NAN:
    return "FP_NAN";
  case TRIO_FP_NORMAL:
    return "FP_NORMAL";
  case TRIO_FP_SUBNORMAL:
    return "FP_SUBNORMAL";
  case TRIO_FP_ZERO:
    return "FP_ZERO";
  default:
    return "FP_UNKNOWN";
  }
}

static void
print_class
TRIO_ARGS2((prefix, number),
	   TRIO_CONST char *prefix,
	   double number)
{
  printf("%-6s: %s %-15s %g\n",
	 prefix,
	 trio_signbit(number) ? "-" : "+",
	 getClassification(TRIO_FPCLASSIFY(number)),
	 number);
}

int main(TRIO_NOARGS)
{
  double my_nan;
  double my_pinf;
  double my_ninf;
# if defined(TRIO_PLATFORM_UNIX)
  void (*signal_handler) TRIO_PROTO((int));
# endif

  my_nan = trio_nan();
  my_pinf = trio_pinf();
  my_ninf = trio_ninf();

  print_class("Nan", my_nan);
  print_class("PInf", my_pinf);
  print_class("NInf", my_ninf);
  print_class("PZero", 0.0);
  print_class("NZero", -0.0);
  print_class("PNorm", 1.0);
  print_class("NNorm", -1.0);
  print_class("PSub", 1.01e-307 - 1.00e-307);
  print_class("NSub", 1.00e-307 - 1.01e-307);
  
  printf("NaN : %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_nan,
	 ((unsigned char *)&my_nan)[0],
	 ((unsigned char *)&my_nan)[1],
	 ((unsigned char *)&my_nan)[2],
	 ((unsigned char *)&my_nan)[3],
	 ((unsigned char *)&my_nan)[4],
	 ((unsigned char *)&my_nan)[5],
	 ((unsigned char *)&my_nan)[6],
	 ((unsigned char *)&my_nan)[7],
	 trio_isnan(my_nan), trio_isinf(my_nan));
  printf("PInf: %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_pinf,
	 ((unsigned char *)&my_pinf)[0],
	 ((unsigned char *)&my_pinf)[1],
	 ((unsigned char *)&my_pinf)[2],
	 ((unsigned char *)&my_pinf)[3],
	 ((unsigned char *)&my_pinf)[4],
	 ((unsigned char *)&my_pinf)[5],
	 ((unsigned char *)&my_pinf)[6],
	 ((unsigned char *)&my_pinf)[7],
	 trio_isnan(my_pinf), trio_isinf(my_pinf));
  printf("NInf: %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_ninf,
	 ((unsigned char *)&my_ninf)[0],
	 ((unsigned char *)&my_ninf)[1],
	 ((unsigned char *)&my_ninf)[2],
	 ((unsigned char *)&my_ninf)[3],
	 ((unsigned char *)&my_ninf)[4],
	 ((unsigned char *)&my_ninf)[5],
	 ((unsigned char *)&my_ninf)[6],
	 ((unsigned char *)&my_ninf)[7],
	 trio_isnan(my_ninf), trio_isinf(my_ninf));
  
# if defined(TRIO_PLATFORM_UNIX)
  signal_handler = signal(SIGFPE, SIG_IGN);
# endif
  
  my_pinf = DBL_MAX + DBL_MAX;
  my_ninf = -my_pinf;
  my_nan = my_pinf / my_pinf;

# if defined(TRIO_PLATFORM_UNIX)
  signal(SIGFPE, signal_handler);
# endif
  
  printf("NaN : %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_nan,
	 ((unsigned char *)&my_nan)[0],
	 ((unsigned char *)&my_nan)[1],
	 ((unsigned char *)&my_nan)[2],
	 ((unsigned char *)&my_nan)[3],
	 ((unsigned char *)&my_nan)[4],
	 ((unsigned char *)&my_nan)[5],
	 ((unsigned char *)&my_nan)[6],
	 ((unsigned char *)&my_nan)[7],
	 trio_isnan(my_nan), trio_isinf(my_nan));
  printf("PInf: %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_pinf,
	 ((unsigned char *)&my_pinf)[0],
	 ((unsigned char *)&my_pinf)[1],
	 ((unsigned char *)&my_pinf)[2],
	 ((unsigned char *)&my_pinf)[3],
	 ((unsigned char *)&my_pinf)[4],
	 ((unsigned char *)&my_pinf)[5],
	 ((unsigned char *)&my_pinf)[6],
	 ((unsigned char *)&my_pinf)[7],
	 trio_isnan(my_pinf), trio_isinf(my_pinf));
  printf("NInf: %4g 0x%02x%02x%02x%02x%02x%02x%02x%02x (%2d, %2d)\n",
	 my_ninf,
	 ((unsigned char *)&my_ninf)[0],
	 ((unsigned char *)&my_ninf)[1],
	 ((unsigned char *)&my_ninf)[2],
	 ((unsigned char *)&my_ninf)[3],
	 ((unsigned char *)&my_ninf)[4],
	 ((unsigned char *)&my_ninf)[5],
	 ((unsigned char *)&my_ninf)[6],
	 ((unsigned char *)&my_ninf)[7],
	 trio_isnan(my_ninf), trio_isinf(my_ninf));
  
  return 0;
}
#endif