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[/] [openrisc/] [trunk/] [gnu-old/] [gdb-7.1/] [sim/] [rx/] [fpu.c] - Blame information for rev 856

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1 227 jeremybenn
/* fpu.c --- FPU emulator for stand-alone RX simulator.
2
 
3
Copyright (C) 2008, 2009, 2010 Free Software Foundation, Inc.
4
Contributed by Red Hat, Inc.
5
 
6
This file is part of the GNU simulators.
7
 
8
This program is free software; you can redistribute it and/or modify
9
it under the terms of the GNU General Public License as published by
10
the Free Software Foundation; either version 3 of the License, or
11
(at your option) any later version.
12
 
13
This program is distributed in the hope that it will be useful,
14
but WITHOUT ANY WARRANTY; without even the implied warranty of
15
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
16
GNU General Public License for more details.
17
 
18
You should have received a copy of the GNU General Public License
19
along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
20
 
21
#include <stdio.h>
22
#include <stdlib.h>
23
 
24
#include "cpu.h"
25
#include "fpu.h"
26
 
27
/* FPU encodings are as follows:
28
 
29
   S EXPONENT MANTISSA
30
   1 12345678 12345678901234567890123
31
 
32
 
33
   1 00000000 00000000000000000000000   -0
34
 
35
   X 00000000 00000000000000000000001   Denormals
36
   X 00000000 11111111111111111111111
37
 
38
   X 00000001 XXXXXXXXXXXXXXXXXXXXXXX   Normals
39
   X 11111110 XXXXXXXXXXXXXXXXXXXXXXX
40
 
41
 
42
   1 11111111 00000000000000000000000   -Inf
43
 
44
   X 11111111 0XXXXXXXXXXXXXXXXXXXXXX   SNaN (X != 0)
45
   X 11111111 1XXXXXXXXXXXXXXXXXXXXXX   QNaN (X != 0)
46
 
47
*/
48
 
49
#define trace 0
50
#define tprintf if (trace) printf
51
 
52
/* Some magic numbers.  */
53
#define PLUS_MAX   0x7f7fffffUL
54
#define MINUS_MAX  0xff7fffffUL
55
#define PLUS_INF   0x7f800000UL
56
#define MINUS_INF  0xff800000UL
57
#define PLUS_ZERO  0x00000000UL
58
#define MINUS_ZERO 0x80000000UL
59
 
60
#define FP_RAISE(e) fp_raise(FPSWBITS_C##e)
61
static void
62
fp_raise (int mask)
63
{
64
  regs.r_fpsw |= mask;
65
  if (mask != FPSWBITS_CE)
66
    {
67
      if (regs.r_fpsw & (mask << FPSW_CESH))
68
        regs.r_fpsw |= (mask << FPSW_CFSH);
69
      if (regs.r_fpsw & FPSWBITS_FMASK)
70
        regs.r_fpsw |= FPSWBITS_FSUM;
71
      else
72
        regs.r_fpsw &= ~FPSWBITS_FSUM;
73
    }
74
}
75
 
76
/* We classify all numbers as one of these.  They correspond to the
77
   rows/colums in the exception tables.  */
78
typedef enum {
79
  FP_NORMAL,
80
  FP_PZERO,
81
  FP_NZERO,
82
  FP_PINFINITY,
83
  FP_NINFINITY,
84
  FP_DENORMAL,
85
  FP_QNAN,
86
  FP_SNAN
87
} FP_Type;
88
 
89
#if defined DEBUG0
90
static const char *fpt_names[] = {
91
  "Normal", "+0", "-0", "+Inf", "-Inf", "Denormal", "QNaN", "SNaN"
92
};
93
#endif
94
 
95
#define EXP_BIAS  127
96
#define EXP_ZERO -127
97
#define EXP_INF   128
98
 
99
#define MANT_BIAS 0x00080000UL
100
 
101
typedef struct {
102
  int exp;
103
  unsigned int mant; /* 24 bits */
104
  char type;
105
  char sign;
106
  fp_t orig_value;
107
} FP_Parts;
108
 
109
static void
110
fp_explode (fp_t f, FP_Parts *p)
111
{
112
  int exp, mant, sign;
113
 
114
  exp = ((f & 0x7f800000UL) >> 23);
115
  mant = f & 0x007fffffUL;
116
  sign = f & 0x80000000UL;
117
  /*printf("explode: %08x %x %2x %6x\n", f, sign, exp, mant);*/
118
 
119
  p->sign = sign ? -1 : 1;
120
  p->exp = exp - EXP_BIAS;
121
  p->orig_value = f;
122
  p->mant = mant | 0x00800000UL;
123
 
124
  if (p->exp == EXP_ZERO)
125
    {
126
      if (regs.r_fpsw & FPSWBITS_DN)
127
        mant = 0;
128
      if (mant)
129
        p->type = FP_DENORMAL;
130
      else
131
        {
132
          p->mant = 0;
133
          p->type = sign ? FP_NZERO : FP_PZERO;
134
        }
135
    }
136
  else if (p->exp == EXP_INF)
137
    {
138
      if (mant == 0)
139
        p->type = sign ? FP_NINFINITY : FP_PINFINITY;
140
      else if (mant & 0x00400000UL)
141
        p->type = FP_QNAN;
142
      else
143
        p->type = FP_SNAN;
144
    }
145
  else
146
    p->type = FP_NORMAL;
147
}
148
 
149
static fp_t
150
fp_implode (FP_Parts *p)
151
{
152
  int exp, mant;
153
 
154
  exp = p->exp + EXP_BIAS;
155
  mant = p->mant;
156
  /*printf("implode: exp %d mant 0x%x\n", exp, mant);*/
157
  if (p->type == FP_NORMAL)
158
    {
159
      while (mant
160
             && exp > 0
161
             && mant < 0x00800000UL)
162
        {
163
          mant <<= 1;
164
          exp --;
165
        }
166
      while (mant > 0x00ffffffUL)
167
        {
168
          mant >>= 1;
169
          exp ++;
170
        }
171
      if (exp < 0)
172
        {
173
          /* underflow */
174
          exp = 0;
175
          mant = 0;
176
          FP_RAISE (E);
177
        }
178
      if (exp >= 255)
179
        {
180
          /* overflow */
181
          exp = 255;
182
          mant = 0;
183
          FP_RAISE (O);
184
        }
185
    }
186
  mant &= 0x007fffffUL;
187
  exp &= 0xff;
188
  mant |= exp << 23;
189
  if (p->sign < 0)
190
    mant |= 0x80000000UL;
191
 
192
  return mant;
193
}
194
 
195
typedef union {
196
  unsigned long long ll;
197
  double d;
198
} U_d_ll;
199
 
200
static int checked_format = 0;
201
 
202
/* We assume a double format like this:
203
   S[1] E[11] M[52]
204
*/
205
 
206
static double
207
fp_to_double (FP_Parts *p)
208
{
209
  U_d_ll u;
210
 
211
  if (!checked_format)
212
    {
213
      u.d = 1.5;
214
      if (u.ll != 0x3ff8000000000000ULL)
215
        abort ();
216
      u.d = -225;
217
      if (u.ll != 0xc06c200000000000ULL)
218
        abort ();
219
      u.d = 10.1;
220
      if (u.ll != 0x4024333333333333ULL)
221
        abort ();
222
      checked_format = 1;
223
    }
224
 
225
  u.ll = 0;
226
  if (p->sign < 0)
227
    u.ll |= (1ULL << 63);
228
  /* Make sure a zero encoding stays a zero.  */
229
  if (p->exp != -EXP_BIAS)
230
    u.ll |= ((unsigned long long)p->exp + 1023ULL) << 52;
231
  u.ll |= (unsigned long long) (p->mant & 0x007fffffUL) << (52 - 23);
232
  return u.d;
233
}
234
 
235
static void
236
double_to_fp (double d, FP_Parts *p)
237
{
238
  int exp;
239
  U_d_ll u;
240
  int sign;
241
 
242
  u.d = d;
243
 
244
  sign = (u.ll & 0x8000000000000000ULL) ? 1 : 0;
245
  exp = u.ll >> 52;
246
  exp = (exp & 0x7ff);
247
 
248
  if (exp == 0)
249
    {
250
      /* A generated denormal should show up as an underflow, not
251
         here.  */
252
      if (sign)
253
        fp_explode (MINUS_ZERO, p);
254
      else
255
        fp_explode (PLUS_ZERO, p);
256
      return;
257
    }
258
 
259
  exp = exp - 1023;
260
  if ((exp + EXP_BIAS) > 254)
261
    {
262
      FP_RAISE (O);
263
      switch (regs.r_fpsw & FPSWBITS_RM)
264
        {
265
        case FPRM_NEAREST:
266
          if (sign)
267
            fp_explode (MINUS_INF, p);
268
          else
269
            fp_explode (PLUS_INF, p);
270
          break;
271
        case FPRM_ZERO:
272
          if (sign)
273
            fp_explode (MINUS_MAX, p);
274
          else
275
            fp_explode (PLUS_MAX, p);
276
          break;
277
        case FPRM_PINF:
278
          if (sign)
279
            fp_explode (MINUS_MAX, p);
280
          else
281
            fp_explode (PLUS_INF, p);
282
          break;
283
        case FPRM_NINF:
284
          if (sign)
285
            fp_explode (MINUS_INF, p);
286
          else
287
            fp_explode (PLUS_MAX, p);
288
          break;
289
        }
290
      return;
291
    }
292
  if ((exp + EXP_BIAS) < 1)
293
    {
294
      if (sign)
295
        fp_explode (MINUS_ZERO, p);
296
      else
297
        fp_explode (PLUS_ZERO, p);
298
      FP_RAISE (U);
299
    }
300
 
301
  p->sign = sign ? -1 : 1;
302
  p->exp = exp;
303
  p->mant = u.ll >> (52-23) & 0x007fffffUL;
304
  p->mant |= 0x00800000UL;
305
  p->type = FP_NORMAL;
306
 
307
  if (u.ll & 0x1fffffffULL)
308
    {
309
      switch (regs.r_fpsw & FPSWBITS_RM)
310
        {
311
        case FPRM_NEAREST:
312
          if (u.ll & 0x10000000ULL)
313
            p->mant ++;
314
          break;
315
        case FPRM_ZERO:
316
          break;
317
        case FPRM_PINF:
318
          if (sign == 1)
319
            p->mant ++;
320
          break;
321
        case FPRM_NINF:
322
          if (sign == -1)
323
            p->mant ++;
324
          break;
325
        }
326
      FP_RAISE (X);
327
    }
328
 
329
}
330
 
331
typedef enum {
332
  eNR,          /* Use the normal result.  */
333
  ePZ, eNZ,     /* +- zero */
334
  eSZ,          /* signed zero - XOR signs of ops together.  */
335
  eRZ,          /* +- zero depending on rounding mode.  */
336
  ePI, eNI,     /* +- Infinity */
337
  eSI,          /* signed infinity - XOR signs of ops together.  */
338
  eQN, eSN,     /* Quiet/Signalling NANs */
339
  eIn,          /* Invalid.  */
340
  eUn,          /* Unimplemented.  */
341
  eDZ,          /* Divide-by-zero.  */
342
  eLT,          /* less than */
343
  eGT,          /* greater than */
344
  eEQ,          /* equal to */
345
} FP_ExceptionCases;
346
 
347
#if defined DEBUG0
348
static const char *ex_names[] = {
349
  "NR", "PZ", "NZ", "SZ", "RZ", "PI", "NI", "SI", "QN", "SN", "IN", "Un", "DZ", "LT", "GT", "EQ"
350
};
351
#endif
352
 
353
/* This checks for all exceptional cases (not all FP exceptions) and
354
   returns TRUE if it is providing the result in *c.  If it returns
355
   FALSE, the caller should do the "normal" operation.  */
356
int
357
check_exceptions (FP_Parts *a, FP_Parts *b, fp_t *c,
358
                  FP_ExceptionCases ex_tab[5][5],
359
                  FP_ExceptionCases *case_ret)
360
{
361
  FP_ExceptionCases fpec;
362
 
363
  if (a->type == FP_SNAN
364
      || b->type == FP_SNAN)
365
    fpec = eIn;
366
  else if (a->type == FP_QNAN
367
           || b->type == FP_QNAN)
368
    fpec = eQN;
369
  else if (a->type == FP_DENORMAL
370
           || b->type == FP_DENORMAL)
371
    fpec = eUn;
372
  else
373
    fpec = ex_tab[(int)(a->type)][(int)(b->type)];
374
 
375
  /*printf("%s %s -> %s\n", fpt_names[(int)(a->type)], fpt_names[(int)(b->type)], ex_names[(int)(fpec)]);*/
376
 
377
  if (case_ret)
378
    *case_ret = fpec;
379
 
380
  switch (fpec)
381
    {
382
    case eNR:   /* Use the normal result.  */
383
      return 0;
384
 
385
    case ePZ:   /* + zero */
386
      *c = 0x00000000;
387
      return 1;
388
 
389
    case eNZ:   /* - zero */
390
      *c = 0x80000000;
391
      return 1;
392
 
393
    case eSZ:   /* signed zero */
394
      *c = (a->sign == b->sign) ? PLUS_ZERO : MINUS_ZERO;
395
      return 1;
396
 
397
    case eRZ:   /* +- zero depending on rounding mode.  */
398
      if ((regs.r_fpsw & FPSWBITS_RM) == FPRM_NINF)
399
        *c = 0x80000000;
400
      else
401
        *c = 0x00000000;
402
      return 1;
403
 
404
    case ePI:   /* + Infinity */
405
      *c = 0x7F800000;
406
      return 1;
407
 
408
    case eNI:   /* - Infinity */
409
      *c = 0xFF800000;
410
      return 1;
411
 
412
    case eSI:   /* sign Infinity */
413
      *c = (a->sign == b->sign) ? PLUS_INF : MINUS_INF;
414
      return 1;
415
 
416
    case eQN:   /* Quiet NANs */
417
      if (a->type == FP_QNAN)
418
        *c = a->orig_value;
419
      else
420
        *c = b->orig_value;
421
      return 1;
422
 
423
    case eSN:   /* Signalling NANs */
424
      if (a->type == FP_SNAN)
425
        *c = a->orig_value;
426
      else
427
        *c = b->orig_value;
428
      FP_RAISE (V);
429
      return 1;
430
 
431
    case eIn:   /* Invalid.  */
432
      FP_RAISE (V);
433
      if (a->type == FP_SNAN)
434
        *c = a->orig_value | 0x00400000;
435
      else if  (a->type == FP_SNAN)
436
        *c = b->orig_value | 0x00400000;
437
      else
438
        *c = 0x7fc00000;
439
      return 1;
440
 
441
    case eUn:   /* Unimplemented.  */
442
      FP_RAISE (E);
443
      return 1;
444
 
445
    case eDZ:   /* Division-by-zero.  */
446
      *c = (a->sign == b->sign) ? PLUS_INF : MINUS_INF;
447
      FP_RAISE (Z);
448
      return 1;
449
 
450
    default:
451
      return 0;
452
    }
453
}
454
 
455
#define CHECK_EXCEPTIONS(FPPa, FPPb, fpc, ex_tab) \
456
  if (check_exceptions (&FPPa, &FPPb, &fpc, ex_tab, 0))  \
457
    return fpc;
458
 
459
/* For each operation, we have two tables of how nonnormal cases are
460
   handled.  The DN=0 case is first, followed by the DN=1 case, with
461
   each table using the following layout: */
462
 
463
static FP_ExceptionCases ex_add_tab[5][5] = {
464
  /* N   +0   -0   +In  -In */
465
  { eNR, eNR, eNR, ePI, eNI }, /* Normal */
466
  { eNR, ePZ, eRZ, ePI, eNI }, /* +0   */
467
  { eNR, eRZ, eNZ, ePI, eNI }, /* -0   */
468
  { ePI, ePI, ePI, ePI, eIn }, /* +Inf */
469
  { eNI, eNI, eNI, eIn, eNI }, /* -Inf */
470
};
471
 
472
fp_t
473
rxfp_add (fp_t fa, fp_t fb)
474
{
475
  FP_Parts a, b, c;
476
  fp_t rv;
477
  double da, db;
478
 
479
  fp_explode (fa, &a);
480
  fp_explode (fb, &b);
481
  CHECK_EXCEPTIONS (a, b, rv, ex_add_tab);
482
 
483
  da = fp_to_double (&a);
484
  db = fp_to_double (&b);
485
  tprintf("%g + %g = %g\n", da, db, da+db);
486
 
487
  double_to_fp (da+db, &c);
488
  rv = fp_implode (&c);
489
  return rv;
490
}
491
 
492
static FP_ExceptionCases ex_sub_tab[5][5] = {
493
  /* N   +0   -0   +In  -In */
494
  { eNR, eNR, eNR, eNI, ePI }, /* Normal */
495
  { eNR, eRZ, ePZ, eNI, ePI }, /* +0   */
496
  { eNR, eNZ, eRZ, eNI, ePI }, /* -0   */
497
  { ePI, ePI, ePI, eIn, ePI }, /* +Inf */
498
  { eNI, eNI, eNI, eNI, eIn }, /* -Inf */
499
};
500
 
501
fp_t
502
rxfp_sub (fp_t fa, fp_t fb)
503
{
504
  FP_Parts a, b, c;
505
  fp_t rv;
506
  double da, db;
507
 
508
  fp_explode (fa, &a);
509
  fp_explode (fb, &b);
510
  CHECK_EXCEPTIONS (a, b, rv, ex_sub_tab);
511
 
512
  da = fp_to_double (&a);
513
  db = fp_to_double (&b);
514
  tprintf("%g - %g = %g\n", da, db, da-db);
515
 
516
  double_to_fp (da-db, &c);
517
  rv = fp_implode (&c);
518
 
519
  return rv;
520
}
521
 
522
static FP_ExceptionCases ex_mul_tab[5][5] = {
523
  /* N   +0   -0   +In  -In */
524
  { eNR, eNR, eNR, eSI, eSI }, /* Normal */
525
  { eNR, ePZ, eNZ, eIn, eIn }, /* +0   */
526
  { eNR, eNZ, ePZ, eIn, eIn }, /* -0   */
527
  { eSI, eIn, eIn, ePI, eNI }, /* +Inf */
528
  { eSI, eIn, eIn, eNI, ePI }, /* -Inf */
529
};
530
 
531
fp_t
532
rxfp_mul (fp_t fa, fp_t fb)
533
{
534
  FP_Parts a, b, c;
535
  fp_t rv;
536
  double da, db;
537
 
538
  fp_explode (fa, &a);
539
  fp_explode (fb, &b);
540
  CHECK_EXCEPTIONS (a, b, rv, ex_mul_tab);
541
 
542
  da = fp_to_double (&a);
543
  db = fp_to_double (&b);
544
  tprintf("%g x %g = %g\n", da, db, da*db);
545
 
546
  double_to_fp (da*db, &c);
547
  rv = fp_implode (&c);
548
 
549
  return rv;
550
}
551
 
552
static FP_ExceptionCases ex_div_tab[5][5] = {
553
  /* N   +0   -0   +In  -In */
554
  { eNR, eDZ, eDZ, eSZ, eSZ }, /* Normal */
555
  { eSZ, eIn, eIn, ePZ, eNZ }, /* +0   */
556
  { eSZ, eIn, eIn, eNZ, ePZ }, /* -0   */
557
  { eSI, ePI, eNI, eIn, eIn }, /* +Inf */
558
  { eSI, eNI, ePI, eIn, eIn }, /* -Inf */
559
};
560
 
561
fp_t
562
rxfp_div (fp_t fa, fp_t fb)
563
{
564
  FP_Parts a, b, c;
565
  fp_t rv;
566
  double da, db;
567
 
568
  fp_explode (fa, &a);
569
  fp_explode (fb, &b);
570
  CHECK_EXCEPTIONS (a, b, rv, ex_div_tab);
571
 
572
  da = fp_to_double (&a);
573
  db = fp_to_double (&b);
574
  tprintf("%g / %g = %g\n", da, db, da/db);
575
 
576
  double_to_fp (da/db, &c);
577
  rv = fp_implode (&c);
578
 
579
  return rv;
580
}
581
 
582
static FP_ExceptionCases ex_cmp_tab[5][5] = {
583
  /* N   +0   -0   +In  -In */
584
  { eNR, eNR, eNR, eLT, eGT }, /* Normal */
585
  { eNR, eEQ, eEQ, eLT, eGT }, /* +0   */
586
  { eNR, eEQ, eEQ, eLT, eGT }, /* -0   */
587
  { eGT, eGT, eGT, eEQ, eGT }, /* +Inf */
588
  { eLT, eLT, eLT, eLT, eEQ }, /* -Inf */
589
};
590
 
591
void
592
rxfp_cmp (fp_t fa, fp_t fb)
593
{
594
  FP_Parts a, b;
595
  fp_t c;
596
  FP_ExceptionCases reason;
597
  int flags = 0;
598
  double da, db;
599
 
600
  fp_explode (fa, &a);
601
  fp_explode (fb, &b);
602
 
603
  if (check_exceptions (&a, &b, &c, ex_cmp_tab, &reason))
604
    {
605
      if (reason == eQN)
606
        {
607
          /* Special case - incomparable.  */
608
          set_flags (FLAGBIT_Z | FLAGBIT_S | FLAGBIT_O, FLAGBIT_O);
609
          return;
610
        }
611
      return;
612
    }
613
 
614
  switch (reason)
615
    {
616
    case eEQ:
617
      flags = FLAGBIT_Z;
618
      break;
619
    case eLT:
620
      flags = FLAGBIT_S;
621
      break;
622
    case eGT:
623
      flags = 0;
624
      break;
625
    case eNR:
626
      da = fp_to_double (&a);
627
      db = fp_to_double (&b);
628
      tprintf("fcmp: %g cmp %g\n", da, db);
629
      if (da < db)
630
        flags = FLAGBIT_S;
631
      else if (da == db)
632
        flags = FLAGBIT_Z;
633
      else
634
        flags = 0;
635
      break;
636
    default:
637
      abort();
638
    }
639
 
640
  set_flags (FLAGBIT_Z | FLAGBIT_S | FLAGBIT_O, flags);
641
}
642
 
643
long
644
rxfp_ftoi (fp_t fa, int round_mode)
645
{
646
  FP_Parts a;
647
  fp_t rv;
648
  int sign;
649
  int whole_bits, frac_bits;
650
 
651
  fp_explode (fa, &a);
652
  sign = fa & 0x80000000UL;
653
 
654
  switch (a.type)
655
    {
656
    case FP_NORMAL:
657
      break;
658
    case FP_PZERO:
659
    case FP_NZERO:
660
      return 0;
661
    case FP_PINFINITY:
662
      FP_RAISE (V);
663
      return 0x7fffffffL;
664
    case FP_NINFINITY:
665
      FP_RAISE (V);
666
      return 0x80000000L;
667
    case FP_DENORMAL:
668
      FP_RAISE (E);
669
      return 0;
670
    case FP_QNAN:
671
    case FP_SNAN:
672
      FP_RAISE (V);
673
      return sign ? 0x80000000U : 0x7fffffff;
674
    }
675
 
676
  if (a.exp >= 31)
677
    {
678
      FP_RAISE (V);
679
      return sign ? 0x80000000U : 0x7fffffff;
680
    }
681
 
682
  a.exp -= 23;
683
 
684
  if (a.exp <= -25)
685
    {
686
      /* Less than 0.49999 */
687
      frac_bits = a.mant;
688
      whole_bits = 0;
689
    }
690
  else if (a.exp < 0)
691
    {
692
      frac_bits = a.mant << (32 + a.exp);
693
      whole_bits = a.mant >> (-a.exp);
694
    }
695
  else
696
    {
697
      frac_bits = 0;
698
      whole_bits = a.mant << a.exp;
699
    }
700
 
701
  if (frac_bits)
702
    {
703
      switch (round_mode & 3)
704
        {
705
        case FPRM_NEAREST:
706
          if (frac_bits & 0x80000000UL)
707
            whole_bits ++;
708
          break;
709
        case FPRM_ZERO:
710
          break;
711
        case FPRM_PINF:
712
          if (!sign)
713
            whole_bits ++;
714
          break;
715
        case FPRM_NINF:
716
          if (sign)
717
            whole_bits ++;
718
          break;
719
        }
720
    }
721
 
722
  rv = sign ? -whole_bits : whole_bits;
723
 
724
  return rv;
725
}
726
 
727
fp_t
728
rxfp_itof (long fa, int round_mode)
729
{
730
  fp_t rv;
731
  int sign = 0;
732
  unsigned int frac_bits;
733
  volatile unsigned int whole_bits;
734
  FP_Parts a;
735
 
736
  if (fa == 0)
737
    return PLUS_ZERO;
738
 
739
  if (fa < 0)
740
    {
741
      fa = -fa;
742
      sign = 1;
743
      a.sign = -1;
744
    }
745
  else
746
    a.sign = 1;
747
 
748
  whole_bits = fa;
749
  a.exp = 31;
750
 
751
  while (! (whole_bits & 0x80000000UL))
752
    {
753
      a.exp --;
754
      whole_bits <<= 1;
755
    }
756
  frac_bits = whole_bits & 0xff;
757
  whole_bits = whole_bits >> 8;
758
 
759
  if (frac_bits)
760
    {
761
      /* We must round */
762
      switch (round_mode & 3)
763
        {
764
        case FPRM_NEAREST:
765
          if (frac_bits & 0x80)
766
            whole_bits ++;
767
          break;
768
        case FPRM_ZERO:
769
          break;
770
        case FPRM_PINF:
771
          if (!sign)
772
            whole_bits ++;
773
          break;
774
        case FPRM_NINF:
775
          if (sign)
776
            whole_bits ++;
777
          break;
778
        }
779
    }
780
 
781
  a.mant = whole_bits;
782
  if (whole_bits & 0xff000000UL)
783
    {
784
      a.mant >>= 1;
785
      a.exp ++;
786
    }
787
 
788
  rv = fp_implode (&a);
789
  return rv;
790
}
791
 

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