libiberty/floatformat.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright (C) 1991-2023 Free Software Foundation, Inc.
   3
   4 This file is part of GDB.
   5
   6 This program is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or
   9 (at your option) any later version.
  10
  11 This program is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with this program; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */
  19
  20 /* This is needed to pick up the NAN macro on some systems.  */
  21 #ifndef _GNU_SOURCE
  22 #define _GNU_SOURCE
  23 #endif
  24
  25 #ifdef HAVE_CONFIG_H
  26 #include "config.h"
  27 #endif
  28
  29 #include <math.h>
  30
  31 #ifdef HAVE_STRING_H
  32 #include <string.h>
  33 #endif
  34
  35 /* On some platforms, <float.h> provides DBL_QNAN.  */
  36 #ifdef STDC_HEADERS
  37 #include <float.h>
  38 #endif
  39
  40 #include "ansidecl.h"
  41 #include "libiberty.h"
  42 #include "floatformat.h"
  43
  44 #ifndef INFINITY
  45 #ifdef HUGE_VAL
  46 #define INFINITY HUGE_VAL
  47 #else
  48 #define INFINITY (1.0 / 0.0)
  49 #endif
  50 #endif
  51
  52 #ifndef NAN
  53 #ifdef DBL_QNAN
  54 #define NAN DBL_QNAN
  55 #else
  56 #define NAN (0.0 / 0.0)
  57 #endif
  58 #endif
  59
  60 static int mant_bits_set (const struct floatformat *, const unsigned char *);
  61 static unsigned long get_field (const unsigned char *,
  62                                 enum floatformat_byteorders,
  63                                 unsigned int,
  64                                 unsigned int,
  65                                 unsigned int);
  66 static int floatformat_always_valid (const struct floatformat *fmt,
  67                                      const void *from);
  68
  69 static int
  70 floatformat_always_valid (const struct floatformat *fmt ATTRIBUTE_UNUSED,
  71                           const void *from ATTRIBUTE_UNUSED)
  72 {
  73   return 1;
  74 }
  75
  76 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
  77    going to bother with trying to muck around with whether it is defined in
  78    a system header, what we do if not, etc.  */
  79 #define FLOATFORMAT_CHAR_BIT 8
  80
  81 /* floatformats for IEEE half, single, double and quad, big and little endian.  */
  82 const struct floatformat floatformat_ieee_half_big =
  83 {
  84   floatformat_big, 16, 0, 1, 5, 15, 31, 6, 10,
  85   floatformat_intbit_no,
  86   "floatformat_ieee_half_big",
  87   floatformat_always_valid,
  88   NULL
  89 };
  90 const struct floatformat floatformat_ieee_half_little =
  91 {
  92   floatformat_little, 16, 0, 1, 5, 15, 31, 6, 10,
  93   floatformat_intbit_no,
  94   "floatformat_ieee_half_little",
  95   floatformat_always_valid,
  96   NULL
  97 };
  98 const struct floatformat floatformat_ieee_single_big =
  99 {
 100   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
 101   floatformat_intbit_no,
 102   "floatformat_ieee_single_big",
 103   floatformat_always_valid,
 104   NULL
 105 };
 106 const struct floatformat floatformat_ieee_single_little =
 107 {
 108   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
 109   floatformat_intbit_no,
 110   "floatformat_ieee_single_little",
 111   floatformat_always_valid,
 112   NULL
 113 };
 114 const struct floatformat floatformat_ieee_double_big =
 115 {
 116   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
 117   floatformat_intbit_no,
 118   "floatformat_ieee_double_big",
 119   floatformat_always_valid,
 120   NULL
 121 };
 122 const struct floatformat floatformat_ieee_double_little =
 123 {
 124   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
 125   floatformat_intbit_no,
 126   "floatformat_ieee_double_little",
 127   floatformat_always_valid,
 128   NULL
 129 };
 130 const struct floatformat floatformat_ieee_quad_big =
 131 {
 132   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 133   floatformat_intbit_no,
 134   "floatformat_ieee_quad_big",
 135   floatformat_always_valid,
 136   NULL
 137 };
 138 const struct floatformat floatformat_ieee_quad_little =
 139 {
 140   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 141   floatformat_intbit_no,
 142   "floatformat_ieee_quad_little",
 143   floatformat_always_valid,
 144   NULL
 145 };
 146
 147 /* floatformat for IEEE double, little endian byte order, with big endian word
 148    ordering, as on the ARM.  */
 149
 150 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
 151 {
 152   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
 153   floatformat_intbit_no,
 154   "floatformat_ieee_double_littlebyte_bigword",
 155   floatformat_always_valid,
 156   NULL
 157 };
 158
 159 /* floatformat for VAX.  Not quite IEEE, but close enough.  */
 160
 161 const struct floatformat floatformat_vax_f =
 162 {
 163   floatformat_vax, 32, 0, 1, 8, 129, 0, 9, 23,
 164   floatformat_intbit_no,
 165   "floatformat_vax_f",
 166   floatformat_always_valid,
 167   NULL
 168 };
 169 const struct floatformat floatformat_vax_d =
 170 {
 171   floatformat_vax, 64, 0, 1, 8, 129, 0, 9, 55,
 172   floatformat_intbit_no,
 173   "floatformat_vax_d",
 174   floatformat_always_valid,
 175   NULL
 176 };
 177 const struct floatformat floatformat_vax_g =
 178 {
 179   floatformat_vax, 64, 0, 1, 11, 1025, 0, 12, 52,
 180   floatformat_intbit_no,
 181   "floatformat_vax_g",
 182   floatformat_always_valid,
 183   NULL
 184 };
 185
 186 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt,
 187                                           const void *from);
 188
 189 static int
 190 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const void *from)
 191 {
 192   /* In the i387 double-extended format, if the exponent is all ones,
 193      then the integer bit must be set.  If the exponent is neither 0
 194      nor ~0, the intbit must also be set.  Only if the exponent is
 195      zero can it be zero, and then it must be zero.  */
 196   unsigned long exponent, int_bit;
 197   const unsigned char *ufrom = (const unsigned char *) from;
 198
 199   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 200                         fmt->exp_start, fmt->exp_len);
 201   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 202                        fmt->man_start, 1);
 203
 204   if ((exponent == 0) != (int_bit == 0))
 205     return 0;
 206   else
 207     return 1;
 208 }
 209
 210 const struct floatformat floatformat_i387_ext =
 211 {
 212   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 213   floatformat_intbit_yes,
 214   "floatformat_i387_ext",
 215   floatformat_i387_ext_is_valid,
 216   NULL
 217 };
 218 const struct floatformat floatformat_m68881_ext =
 219 {
 220   /* Note that the bits from 16 to 31 are unused.  */
 221   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
 222   floatformat_intbit_yes,
 223   "floatformat_m68881_ext",
 224   floatformat_always_valid,
 225   NULL
 226 };
 227 const struct floatformat floatformat_i960_ext =
 228 {
 229   /* Note that the bits from 0 to 15 are unused.  */
 230   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
 231   floatformat_intbit_yes,
 232   "floatformat_i960_ext",
 233   floatformat_always_valid,
 234   NULL
 235 };
 236 const struct floatformat floatformat_m88110_ext =
 237 {
 238   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 239   floatformat_intbit_yes,
 240   "floatformat_m88110_ext",
 241   floatformat_always_valid,
 242   NULL
 243 };
 244 const struct floatformat floatformat_m88110_harris_ext =
 245 {
 246   /* Harris uses raw format 128 bytes long, but the number is just an ieee
 247      double, and the last 64 bits are wasted. */
 248   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
 249   floatformat_intbit_no,
 250   "floatformat_m88110_ext_harris",
 251   floatformat_always_valid,
 252   NULL
 253 };
 254 const struct floatformat floatformat_arm_ext_big =
 255 {
 256   /* Bits 1 to 16 are unused.  */
 257   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 258   floatformat_intbit_yes,
 259   "floatformat_arm_ext_big",
 260   floatformat_always_valid,
 261   NULL
 262 };
 263 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 264 {
 265   /* Bits 1 to 16 are unused.  */
 266   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 267   floatformat_intbit_yes,
 268   "floatformat_arm_ext_littlebyte_bigword",
 269   floatformat_always_valid,
 270   NULL
 271 };
 272 const struct floatformat floatformat_ia64_spill_big =
 273 {
 274   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 275   floatformat_intbit_yes,
 276   "floatformat_ia64_spill_big",
 277   floatformat_always_valid,
 278   NULL
 279 };
 280 const struct floatformat floatformat_ia64_spill_little =
 281 {
 282   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 283   floatformat_intbit_yes,
 284   "floatformat_ia64_spill_little",
 285   floatformat_always_valid,
 286   NULL
 287 };
 288
 289 static int
 290 floatformat_ibm_long_double_is_valid (const struct floatformat *fmt,
 291                                       const void *from)
 292 {
 293   const unsigned char *ufrom = (const unsigned char *) from;
 294   const struct floatformat *hfmt = fmt->split_half;
 295   long top_exp, bot_exp;
 296   int top_nan = 0;
 297
 298   top_exp = get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 299                        hfmt->exp_start, hfmt->exp_len);
 300   bot_exp = get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
 301                        hfmt->exp_start, hfmt->exp_len);
 302
 303   if ((unsigned long) top_exp == hfmt->exp_nan)
 304     top_nan = mant_bits_set (hfmt, ufrom);
 305
 306   /* A NaN is valid with any low part.  */
 307   if (top_nan)
 308     return 1;
 309
 310   /* An infinity, zero or denormal requires low part 0 (positive or
 311      negative).  */
 312   if ((unsigned long) top_exp == hfmt->exp_nan || top_exp == 0)
 313     {
 314       if (bot_exp != 0)
 315         return 0;
 316
 317       return !mant_bits_set (hfmt, ufrom + 8);
 318     }
 319
 320   /* The top part is now a finite normal value.  The long double value
 321      is the sum of the two parts, and the top part must equal the
 322      result of rounding the long double value to nearest double.  Thus
 323      the bottom part must be <= 0.5ulp of the top part in absolute
 324      value, and if it is < 0.5ulp then the long double is definitely
 325      valid.  */
 326   if (bot_exp < top_exp - 53)
 327     return 1;
 328   if (bot_exp > top_exp - 53 && bot_exp != 0)
 329     return 0;
 330   if (bot_exp == 0)
 331     {
 332       /* The bottom part is 0 or denormal.  Determine which, and if
 333          denormal the first two set bits.  */
 334       int first_bit = -1, second_bit = -1, cur_bit;
 335       for (cur_bit = 0; (unsigned int) cur_bit < hfmt->man_len; cur_bit++)
 336         if (get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
 337                        hfmt->man_start + cur_bit, 1))
 338           {
 339             if (first_bit == -1)
 340               first_bit = cur_bit;
 341             else
 342               {
 343                 second_bit = cur_bit;
 344                 break;
 345               }
 346           }
 347       /* Bottom part 0 is OK.  */
 348       if (first_bit == -1)
 349         return 1;
 350       /* The real exponent of the bottom part is -first_bit.  */
 351       if (-first_bit < top_exp - 53)
 352         return 1;
 353       if (-first_bit > top_exp - 53)
 354         return 0;
 355       /* The bottom part is at least 0.5ulp of the top part.  For this
 356          to be OK, the bottom part must be exactly 0.5ulp (i.e. no
 357          more bits set) and the top part must have last bit 0.  */
 358       if (second_bit != -1)
 359         return 0;
 360       return !get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 361                          hfmt->man_start + hfmt->man_len - 1, 1);
 362     }
 363   else
 364     {
 365       /* The bottom part is at least 0.5ulp of the top part.  For this
 366          to be OK, it must be exactly 0.5ulp (i.e. no explicit bits
 367          set) and the top part must have last bit 0.  */
 368       if (get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 369                      hfmt->man_start + hfmt->man_len - 1, 1))
 370         return 0;
 371       return !mant_bits_set (hfmt, ufrom + 8);
 372     }
 373 }
 374
 375 const struct floatformat floatformat_ibm_long_double_big =
 376 {
 377   floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52,
 378   floatformat_intbit_no,
 379   "floatformat_ibm_long_double_big",
 380   floatformat_ibm_long_double_is_valid,
 381   &floatformat_ieee_double_big
 382 };
 383
 384 const struct floatformat floatformat_ibm_long_double_little =
 385 {
 386   floatformat_little, 128, 0, 1, 11, 1023, 2047, 12, 52,
 387   floatformat_intbit_no,
 388   "floatformat_ibm_long_double_little",
 389   floatformat_ibm_long_double_is_valid,
 390   &floatformat_ieee_double_little
 391 };
 392
 393 const struct floatformat floatformat_bfloat16_big =
 394 {
 395   floatformat_big, 16, 0, 1, 8, 127, 255, 9, 7,
 396   floatformat_intbit_no,
 397   "floatformat_bfloat16_big",
 398   floatformat_always_valid,
 399   NULL
 400 };
 401
 402 const struct floatformat floatformat_bfloat16_little =
 403 {
 404   floatformat_little, 16, 0, 1, 8, 127, 255, 9, 7,
 405   floatformat_intbit_no,
 406   "floatformat_bfloat16_little",
 407   floatformat_always_valid,
 408   NULL
 409 };
 410
 411 #ifndef min
 412 #define min(a, b) ((a) < (b) ? (a) : (b))
 413 #endif
 414
 415 /* Return 1 if any bits are explicitly set in the mantissa of UFROM,
 416    format FMT, 0 otherwise.  */
 417 static int
 418 mant_bits_set (const struct floatformat *fmt, const unsigned char *ufrom)
 419 {
 420   unsigned int mant_bits, mant_off;
 421   int mant_bits_left;
 422
 423   mant_off = fmt->man_start;
 424   mant_bits_left = fmt->man_len;
 425   while (mant_bits_left > 0)
 426     {
 427       mant_bits = min (mant_bits_left, 32);
 428
 429       if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
 430                      mant_off, mant_bits) != 0)
 431         return 1;
 432
 433       mant_off += mant_bits;
 434       mant_bits_left -= mant_bits;
 435     }
 436   return 0;
 437 }
 438
 439 /* Extract a field which starts at START and is LEN bits long.  DATA and
 440    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 441 static unsigned long
 442 get_field (const unsigned char *data, enum floatformat_byteorders order,
 443            unsigned int total_len, unsigned int start, unsigned int len)
 444 {
 445   unsigned long result = 0;
 446   unsigned int cur_byte;
 447   int lo_bit, hi_bit, cur_bitshift = 0;
 448   int nextbyte = (order == floatformat_little) ? 1 : -1;
 449
 450   /* Start is in big-endian bit order!  Fix that first.  */
 451   start = total_len - (start + len);
 452
 453   /* Start at the least significant part of the field.  */
 454   if (order == floatformat_little)
 455     cur_byte = start / FLOATFORMAT_CHAR_BIT;
 456   else
 457     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
 458
 459   lo_bit = start % FLOATFORMAT_CHAR_BIT;
 460   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
 461
 462   do
 463     {
 464       unsigned int shifted = *(data + cur_byte) >> lo_bit;
 465       unsigned int bits = hi_bit - lo_bit;
 466       unsigned int mask = (1 << bits) - 1;
 467       result |= (shifted & mask) << cur_bitshift;
 468       len -= bits;
 469       cur_bitshift += bits;
 470       cur_byte += nextbyte;
 471       lo_bit = 0;
 472       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
 473     }
 474   while (len != 0);
 475
 476   return result;
 477 }
 478
 479 /* Convert from FMT to a double.
 480    FROM is the address of the extended float.
 481    Store the double in *TO.  */
 482
 483 void
 484 floatformat_to_double (const struct floatformat *fmt,
 485                        const void *from, double *to)
 486 {
 487   const unsigned char *ufrom = (const unsigned char *) from;
 488   double dto;
 489   long exponent;
 490   unsigned long mant;
 491   unsigned int mant_bits, mant_off;
 492   int mant_bits_left;
 493
 494   /* Split values are not handled specially, since the top half has
 495      the correctly rounded double value (in the only supported case of
 496      split values).  */
 497
 498   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 499                         fmt->exp_start, fmt->exp_len);
 500
 501   /* If the exponent indicates a NaN, we don't have information to
 502      decide what to do.  So we handle it like IEEE, except that we
 503      don't try to preserve the type of NaN.  FIXME.  */
 504   if ((unsigned long) exponent == fmt->exp_nan)
 505     {
 506       int nan = mant_bits_set (fmt, ufrom);
 507
 508       /* On certain systems (such as GNU/Linux), the use of the
 509          INFINITY macro below may generate a warning that cannot be
 510          silenced due to a bug in GCC (PR preprocessor/11931).  The
 511          preprocessor fails to recognise the __extension__ keyword in
 512          conjunction with the GNU/C99 extension for hexadecimal
 513          floating point constants and will issue a warning when
 514          compiling with -pedantic.  */
 515       if (nan)
 516         dto = NAN;
 517       else
 518         dto = INFINITY;
 519
 520       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 521         dto = -dto;
 522
 523       *to = dto;
 524
 525       return;
 526     }
 527
 528   mant_bits_left = fmt->man_len;
 529   mant_off = fmt->man_start;
 530   dto = 0.0;
 531
 532   /* Build the result algebraically.  Might go infinite, underflow, etc;
 533      who cares. */
 534
 535   /* For denorms use minimum exponent.  */
 536   if (exponent == 0)
 537     exponent = 1 - fmt->exp_bias;
 538   else
 539     {
 540       exponent -= fmt->exp_bias;
 541
 542       /* If this format uses a hidden bit, explicitly add it in now.
 543          Otherwise, increment the exponent by one to account for the
 544          integer bit.  */
 545
 546       if (fmt->intbit == floatformat_intbit_no)
 547         dto = ldexp (1.0, exponent);
 548       else
 549         exponent++;
 550     }
 551
 552   while (mant_bits_left > 0)
 553     {
 554       mant_bits = min (mant_bits_left, 32);
 555
 556       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 557                          mant_off, mant_bits);
 558
 559       dto += ldexp ((double) mant, exponent - mant_bits);
 560       exponent -= mant_bits;
 561       mant_off += mant_bits;
 562       mant_bits_left -= mant_bits;
 563     }
 564
 565   /* Negate it if negative.  */
 566   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 567     dto = -dto;
 568   *to = dto;
 569 }
 570 \f
 571 static void put_field (unsigned char *, enum floatformat_byteorders,
 572                        unsigned int,
 573                        unsigned int,
 574                        unsigned int,
 575                        unsigned long);
 576
 577 /* Set a field which starts at START and is LEN bits long.  DATA and
 578    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 579 static void
 580 put_field (unsigned char *data, enum floatformat_byteorders order,
 581            unsigned int total_len, unsigned int start, unsigned int len,
 582            unsigned long stuff_to_put)
 583 {
 584   unsigned int cur_byte;
 585   int lo_bit, hi_bit;
 586   int nextbyte = (order == floatformat_little) ? 1 : -1;
 587
 588   /* Start is in big-endian bit order!  Fix that first.  */
 589   start = total_len - (start + len);
 590
 591   /* Start at the least significant part of the field.  */
 592   if (order == floatformat_little)
 593     cur_byte = start / FLOATFORMAT_CHAR_BIT;
 594   else
 595     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
 596
 597   lo_bit = start % FLOATFORMAT_CHAR_BIT;
 598   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
 599
 600   do
 601     {
 602       unsigned char *byte_ptr = data + cur_byte;
 603       unsigned int bits = hi_bit - lo_bit;
 604       unsigned int mask = ((1 << bits) - 1) << lo_bit;
 605       *byte_ptr = (*byte_ptr & ~mask) | ((stuff_to_put << lo_bit) & mask);
 606       stuff_to_put >>= bits;
 607       len -= bits;
 608       cur_byte += nextbyte;
 609       lo_bit = 0;
 610       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
 611     }
 612   while (len != 0);
 613 }
 614
 615 /* The converse: convert the double *FROM to an extended float
 616    and store where TO points.  Neither FROM nor TO have any alignment
 617    restrictions.  */
 618
 619 void
 620 floatformat_from_double (const struct floatformat *fmt,
 621                          const double *from, void *to)
 622 {
 623   double dfrom;
 624   int exponent;
 625   double mant;
 626   unsigned int mant_bits, mant_off;
 627   int mant_bits_left;
 628   unsigned char *uto = (unsigned char *) to;
 629
 630   dfrom = *from;
 631   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 632
 633   /* Split values are not handled specially, since a bottom half of
 634      zero is correct for any value representable as double (in the
 635      only supported case of split values).  */
 636
 637   /* If negative, set the sign bit.  */
 638   if (dfrom < 0)
 639     {
 640       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 641       dfrom = -dfrom;
 642     }
 643
 644   if (dfrom == 0)
 645     {
 646       /* 0.0.  */
 647       return;
 648     }
 649
 650   if (dfrom != dfrom)
 651     {
 652       /* NaN.  */
 653       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 654                  fmt->exp_len, fmt->exp_nan);
 655       /* Be sure it's not infinity, but NaN value is irrelevant.  */
 656       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 657                  32, 1);
 658       return;
 659     }
 660
 661   if (dfrom + dfrom == dfrom)
 662     {
 663       /* This can only happen for an infinite value (or zero, which we
 664          already handled above).  */
 665       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 666                  fmt->exp_len, fmt->exp_nan);
 667       return;
 668     }
 669
 670   mant = frexp (dfrom, &exponent);
 671   if (exponent + fmt->exp_bias - 1 > 0)
 672     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 673                fmt->exp_len, exponent + fmt->exp_bias - 1);
 674   else
 675     {
 676       /* Handle a denormalized number.  FIXME: What should we do for
 677          non-IEEE formats?  */
 678       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 679                  fmt->exp_len, 0);
 680       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
 681     }
 682
 683   mant_bits_left = fmt->man_len;
 684   mant_off = fmt->man_start;
 685   while (mant_bits_left > 0)
 686     {
 687       unsigned long mant_long;
 688       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 689
 690       mant *= 4294967296.0;
 691       mant_long = (unsigned long)mant;
 692       mant -= mant_long;
 693
 694       /* If the integer bit is implicit, and we are not creating a
 695          denormalized number, then we need to discard it.  */
 696       if ((unsigned int) mant_bits_left == fmt->man_len
 697           && fmt->intbit == floatformat_intbit_no
 698           && exponent + fmt->exp_bias - 1 > 0)
 699         {
 700           mant_long &= 0x7fffffff;
 701           mant_bits -= 1;
 702         }
 703       else if (mant_bits < 32)
 704         {
 705           /* The bits we want are in the most significant MANT_BITS bits of
 706              mant_long.  Move them to the least significant.  */
 707           mant_long >>= 32 - mant_bits;
 708         }
 709
 710       put_field (uto, fmt->byteorder, fmt->totalsize,
 711                  mant_off, mant_bits, mant_long);
 712       mant_off += mant_bits;
 713       mant_bits_left -= mant_bits;
 714     }
 715 }
 716
 717 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
 718
 719 int
 720 floatformat_is_valid (const struct floatformat *fmt, const void *from)
 721 {
 722   return fmt->is_valid (fmt, from);
 723 }
 724
 725
 726 #ifdef IEEE_DEBUG
 727
 728 #include <stdio.h>
 729
 730 /* This is to be run on a host which uses IEEE floating point.  */
 731
 732 void
 733 ieee_test (double n)
 734 {
 735   double result;
 736
 737   floatformat_to_double (&floatformat_ieee_double_little, &n, &result);
 738   if ((n != result && (! isnan (n) || ! isnan (result)))
 739       || (n < 0 && result >= 0)
 740       || (n >= 0 && result < 0))
 741     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 742
 743   floatformat_from_double (&floatformat_ieee_double_little, &n, &result);
 744   if ((n != result && (! isnan (n) || ! isnan (result)))
 745       || (n < 0 && result >= 0)
 746       || (n >= 0 && result < 0))
 747     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 748
 749 #if 0
 750   {
 751     char exten[16];
 752
 753     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 754     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 755     if (n != result)
 756       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 757   }
 758 #endif
 759
 760 #if IEEE_DEBUG > 1
 761   /* This is to be run on a host which uses 68881 format.  */
 762   {
 763     long double ex = *(long double *)exten;
 764     if (ex != n)
 765       printf ("Differ(from vs. extended): %.20g\n", n);
 766   }
 767 #endif
 768 }
 769
 770 int
 771 main (void)
 772 {
 773   ieee_test (0.0);
 774   ieee_test (0.5);
 775   ieee_test (1.1);
 776   ieee_test (256.0);
 777   ieee_test (0.12345);
 778   ieee_test (234235.78907234);
 779   ieee_test (-512.0);
 780   ieee_test (-0.004321);
 781   ieee_test (1.2E-70);
 782   ieee_test (1.2E-316);
 783   ieee_test (4.9406564584124654E-324);
 784   ieee_test (- 4.9406564584124654E-324);
 785   ieee_test (- 0.0);
 786   ieee_test (- INFINITY);
 787   ieee_test (- NAN);
 788   ieee_test (INFINITY);
 789   ieee_test (NAN);
 790   return 0;
 791 }
 792 #endif