libiberty/floatformat.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright 1991, 1994, 1999, 2000, 2003, 2005, 2006, 2010
   3    Free Software Foundation, Inc.
   4
   5 This file is part of GDB.
   6
   7 This program is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2 of the License, or
  10 (at your option) any later version.
  11
  12 This program is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with this program; if not, write to the Free Software
  19 Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */
  20
  21 /* This is needed to pick up the NAN macro on some systems.  */
  22 #define _GNU_SOURCE
  23
  24 #ifdef HAVE_CONFIG_H
  25 #include "config.h"
  26 #endif
  27
  28 #include <math.h>
  29
  30 #ifdef HAVE_STRING_H
  31 #include <string.h>
  32 #endif
  33
  34 /* On some platforms, <float.h> provides DBL_QNAN.  */
  35 #ifdef STDC_HEADERS
  36 #include <float.h>
  37 #endif
  38
  39 #include "ansidecl.h"
  40 #include "libiberty.h"
  41 #include "floatformat.h"
  42
  43 #ifndef INFINITY
  44 #ifdef HUGE_VAL
  45 #define INFINITY HUGE_VAL
  46 #else
  47 #define INFINITY (1.0 / 0.0)
  48 #endif
  49 #endif
  50
  51 #ifndef NAN
  52 #ifdef DBL_QNAN
  53 #define NAN DBL_QNAN
  54 #else
  55 #define NAN (0.0 / 0.0)
  56 #endif
  57 #endif
  58
  59 static int mant_bits_set (const struct floatformat *, const unsigned char *);
  60 static unsigned long get_field (const unsigned char *,
  61                                 enum floatformat_byteorders,
  62                                 unsigned int,
  63                                 unsigned int,
  64                                 unsigned int);
  65 static int floatformat_always_valid (const struct floatformat *fmt,
  66                                      const void *from);
  67
  68 static int
  69 floatformat_always_valid (const struct floatformat *fmt ATTRIBUTE_UNUSED,
  70                           const void *from ATTRIBUTE_UNUSED)
  71 {
  72   return 1;
  73 }
  74
  75 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
  76    going to bother with trying to muck around with whether it is defined in
  77    a system header, what we do if not, etc.  */
  78 #define FLOATFORMAT_CHAR_BIT 8
  79
  80 /* floatformats for IEEE half, single and double, big and little endian.  */
  81 const struct floatformat floatformat_ieee_half_big =
  82 {
  83   floatformat_big, 16, 0, 1, 5, 15, 31, 6, 10,
  84   floatformat_intbit_no,
  85   "floatformat_ieee_half_big",
  86   floatformat_always_valid,
  87   NULL
  88 };
  89 const struct floatformat floatformat_ieee_half_little =
  90 {
  91   floatformat_little, 16, 0, 1, 5, 15, 31, 6, 10,
  92   floatformat_intbit_no,
  93   "floatformat_ieee_half_little",
  94   floatformat_always_valid,
  95   NULL
  96 };
  97 const struct floatformat floatformat_ieee_single_big =
  98 {
  99   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
 100   floatformat_intbit_no,
 101   "floatformat_ieee_single_big",
 102   floatformat_always_valid,
 103   NULL
 104 };
 105 const struct floatformat floatformat_ieee_single_little =
 106 {
 107   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
 108   floatformat_intbit_no,
 109   "floatformat_ieee_single_little",
 110   floatformat_always_valid,
 111   NULL
 112 };
 113 const struct floatformat floatformat_ieee_double_big =
 114 {
 115   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
 116   floatformat_intbit_no,
 117   "floatformat_ieee_double_big",
 118   floatformat_always_valid,
 119   NULL
 120 };
 121 const struct floatformat floatformat_ieee_double_little =
 122 {
 123   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
 124   floatformat_intbit_no,
 125   "floatformat_ieee_double_little",
 126   floatformat_always_valid,
 127   NULL
 128 };
 129
 130 /* floatformat for IEEE double, little endian byte order, with big endian word
 131    ordering, as on the ARM.  */
 132
 133 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
 134 {
 135   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
 136   floatformat_intbit_no,
 137   "floatformat_ieee_double_littlebyte_bigword",
 138   floatformat_always_valid,
 139   NULL
 140 };
 141
 142 /* floatformat for VAX.  Not quite IEEE, but close enough.  */
 143
 144 const struct floatformat floatformat_vax_f =
 145 {
 146   floatformat_vax, 32, 0, 1, 8, 129, 0, 9, 23,
 147   floatformat_intbit_no,
 148   "floatformat_vax_f",
 149   floatformat_always_valid,
 150   NULL
 151 };
 152 const struct floatformat floatformat_vax_d =
 153 {
 154   floatformat_vax, 64, 0, 1, 8, 129, 0, 9, 55,
 155   floatformat_intbit_no,
 156   "floatformat_vax_d",
 157   floatformat_always_valid,
 158   NULL
 159 };
 160 const struct floatformat floatformat_vax_g =
 161 {
 162   floatformat_vax, 64, 0, 1, 11, 1025, 0, 12, 52,
 163   floatformat_intbit_no,
 164   "floatformat_vax_g",
 165   floatformat_always_valid,
 166   NULL
 167 };
 168
 169 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt,
 170                                           const void *from);
 171
 172 static int
 173 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const void *from)
 174 {
 175   /* In the i387 double-extended format, if the exponent is all ones,
 176      then the integer bit must be set.  If the exponent is neither 0
 177      nor ~0, the intbit must also be set.  Only if the exponent is
 178      zero can it be zero, and then it must be zero.  */
 179   unsigned long exponent, int_bit;
 180   const unsigned char *ufrom = (const unsigned char *) from;
 181
 182   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 183                         fmt->exp_start, fmt->exp_len);
 184   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 185                        fmt->man_start, 1);
 186
 187   if ((exponent == 0) != (int_bit == 0))
 188     return 0;
 189   else
 190     return 1;
 191 }
 192
 193 const struct floatformat floatformat_i387_ext =
 194 {
 195   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 196   floatformat_intbit_yes,
 197   "floatformat_i387_ext",
 198   floatformat_i387_ext_is_valid,
 199   NULL
 200 };
 201 const struct floatformat floatformat_m68881_ext =
 202 {
 203   /* Note that the bits from 16 to 31 are unused.  */
 204   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
 205   floatformat_intbit_yes,
 206   "floatformat_m68881_ext",
 207   floatformat_always_valid,
 208   NULL
 209 };
 210 const struct floatformat floatformat_i960_ext =
 211 {
 212   /* Note that the bits from 0 to 15 are unused.  */
 213   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
 214   floatformat_intbit_yes,
 215   "floatformat_i960_ext",
 216   floatformat_always_valid,
 217   NULL
 218 };
 219 const struct floatformat floatformat_m88110_ext =
 220 {
 221   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 222   floatformat_intbit_yes,
 223   "floatformat_m88110_ext",
 224   floatformat_always_valid,
 225   NULL
 226 };
 227 const struct floatformat floatformat_m88110_harris_ext =
 228 {
 229   /* Harris uses raw format 128 bytes long, but the number is just an ieee
 230      double, and the last 64 bits are wasted. */
 231   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
 232   floatformat_intbit_no,
 233   "floatformat_m88110_ext_harris",
 234   floatformat_always_valid,
 235   NULL
 236 };
 237 const struct floatformat floatformat_arm_ext_big =
 238 {
 239   /* Bits 1 to 16 are unused.  */
 240   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 241   floatformat_intbit_yes,
 242   "floatformat_arm_ext_big",
 243   floatformat_always_valid,
 244   NULL
 245 };
 246 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 247 {
 248   /* Bits 1 to 16 are unused.  */
 249   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 250   floatformat_intbit_yes,
 251   "floatformat_arm_ext_littlebyte_bigword",
 252   floatformat_always_valid,
 253   NULL
 254 };
 255 const struct floatformat floatformat_ia64_spill_big =
 256 {
 257   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 258   floatformat_intbit_yes,
 259   "floatformat_ia64_spill_big",
 260   floatformat_always_valid,
 261   NULL
 262 };
 263 const struct floatformat floatformat_ia64_spill_little =
 264 {
 265   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 266   floatformat_intbit_yes,
 267   "floatformat_ia64_spill_little",
 268   floatformat_always_valid,
 269   NULL
 270 };
 271 const struct floatformat floatformat_ia64_quad_big =
 272 {
 273   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 274   floatformat_intbit_no,
 275   "floatformat_ia64_quad_big",
 276   floatformat_always_valid,
 277   NULL
 278 };
 279 const struct floatformat floatformat_ia64_quad_little =
 280 {
 281   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 282   floatformat_intbit_no,
 283   "floatformat_ia64_quad_little",
 284   floatformat_always_valid,
 285   NULL
 286 };
 287
 288 static int
 289 floatformat_ibm_long_double_is_valid (const struct floatformat *fmt,
 290                                       const void *from)
 291 {
 292   const unsigned char *ufrom = (const unsigned char *) from;
 293   const struct floatformat *hfmt = fmt->split_half;
 294   long top_exp, bot_exp;
 295   int top_nan = 0;
 296
 297   top_exp = get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 298                        hfmt->exp_start, hfmt->exp_len);
 299   bot_exp = get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
 300                        hfmt->exp_start, hfmt->exp_len);
 301
 302   if ((unsigned long) top_exp == hfmt->exp_nan)
 303     top_nan = mant_bits_set (hfmt, ufrom);
 304
 305   /* A NaN is valid with any low part.  */
 306   if (top_nan)
 307     return 1;
 308
 309   /* An infinity, zero or denormal requires low part 0 (positive or
 310      negative).  */
 311   if ((unsigned long) top_exp == hfmt->exp_nan || top_exp == 0)
 312     {
 313       if (bot_exp != 0)
 314         return 0;
 315
 316       return !mant_bits_set (hfmt, ufrom + 8);
 317     }
 318
 319   /* The top part is now a finite normal value.  The long double value
 320      is the sum of the two parts, and the top part must equal the
 321      result of rounding the long double value to nearest double.  Thus
 322      the bottom part must be <= 0.5ulp of the top part in absolute
 323      value, and if it is < 0.5ulp then the long double is definitely
 324      valid.  */
 325   if (bot_exp < top_exp - 53)
 326     return 1;
 327   if (bot_exp > top_exp - 53 && bot_exp != 0)
 328     return 0;
 329   if (bot_exp == 0)
 330     {
 331       /* The bottom part is 0 or denormal.  Determine which, and if
 332          denormal the first two set bits.  */
 333       int first_bit = -1, second_bit = -1, cur_bit;
 334       for (cur_bit = 0; (unsigned int) cur_bit < hfmt->man_len; cur_bit++)
 335         if (get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
 336                        hfmt->man_start + cur_bit, 1))
 337           {
 338             if (first_bit == -1)
 339               first_bit = cur_bit;
 340             else
 341               {
 342                 second_bit = cur_bit;
 343                 break;
 344               }
 345           }
 346       /* Bottom part 0 is OK.  */
 347       if (first_bit == -1)
 348         return 1;
 349       /* The real exponent of the bottom part is -first_bit.  */
 350       if (-first_bit < top_exp - 53)
 351         return 1;
 352       if (-first_bit > top_exp - 53)
 353         return 0;
 354       /* The bottom part is at least 0.5ulp of the top part.  For this
 355          to be OK, the bottom part must be exactly 0.5ulp (i.e. no
 356          more bits set) and the top part must have last bit 0.  */
 357       if (second_bit != -1)
 358         return 0;
 359       return !get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 360                          hfmt->man_start + hfmt->man_len - 1, 1);
 361     }
 362   else
 363     {
 364       /* The bottom part is at least 0.5ulp of the top part.  For this
 365          to be OK, it must be exactly 0.5ulp (i.e. no explicit bits
 366          set) and the top part must have last bit 0.  */
 367       if (get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
 368                      hfmt->man_start + hfmt->man_len - 1, 1))
 369         return 0;
 370       return !mant_bits_set (hfmt, ufrom + 8);
 371     }
 372 }
 373
 374 const struct floatformat floatformat_ibm_long_double =
 375 {
 376   floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52,
 377   floatformat_intbit_no,
 378   "floatformat_ibm_long_double",
 379   floatformat_ibm_long_double_is_valid,
 380   &floatformat_ieee_double_big
 381 };
 382 \f
 383
 384 #ifndef min
 385 #define min(a, b) ((a) < (b) ? (a) : (b))
 386 #endif
 387
 388 /* Return 1 if any bits are explicitly set in the mantissa of UFROM,
 389    format FMT, 0 otherwise.  */
 390 static int
 391 mant_bits_set (const struct floatformat *fmt, const unsigned char *ufrom)
 392 {
 393   unsigned int mant_bits, mant_off;
 394   int mant_bits_left;
 395
 396   mant_off = fmt->man_start;
 397   mant_bits_left = fmt->man_len;
 398   while (mant_bits_left > 0)
 399     {
 400       mant_bits = min (mant_bits_left, 32);
 401
 402       if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
 403                      mant_off, mant_bits) != 0)
 404         return 1;
 405
 406       mant_off += mant_bits;
 407       mant_bits_left -= mant_bits;
 408     }
 409   return 0;
 410 }
 411
 412 /* Extract a field which starts at START and is LEN bits long.  DATA and
 413    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 414 static unsigned long
 415 get_field (const unsigned char *data, enum floatformat_byteorders order,
 416            unsigned int total_len, unsigned int start, unsigned int len)
 417 {
 418   unsigned long result = 0;
 419   unsigned int cur_byte;
 420   int lo_bit, hi_bit, cur_bitshift = 0;
 421   int nextbyte = (order == floatformat_little) ? 1 : -1;
 422
 423   /* Start is in big-endian bit order!  Fix that first.  */
 424   start = total_len - (start + len);
 425
 426   /* Start at the least significant part of the field.  */
 427   if (order == floatformat_little)
 428     cur_byte = start / FLOATFORMAT_CHAR_BIT;
 429   else
 430     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
 431
 432   lo_bit = start % FLOATFORMAT_CHAR_BIT;
 433   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
 434
 435   do
 436     {
 437       unsigned int shifted = *(data + cur_byte) >> lo_bit;
 438       unsigned int bits = hi_bit - lo_bit;
 439       unsigned int mask = (1 << bits) - 1;
 440       result |= (shifted & mask) << cur_bitshift;
 441       len -= bits;
 442       cur_bitshift += bits;
 443       cur_byte += nextbyte;
 444       lo_bit = 0;
 445       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
 446     }
 447   while (len != 0);
 448
 449   return result;
 450 }
 451
 452 /* Convert from FMT to a double.
 453    FROM is the address of the extended float.
 454    Store the double in *TO.  */
 455
 456 void
 457 floatformat_to_double (const struct floatformat *fmt,
 458                        const void *from, double *to)
 459 {
 460   const unsigned char *ufrom = (const unsigned char *) from;
 461   double dto;
 462   long exponent;
 463   unsigned long mant;
 464   unsigned int mant_bits, mant_off;
 465   int mant_bits_left;
 466   int special_exponent;         /* It's a NaN, denorm or zero */
 467
 468   /* Split values are not handled specially, since the top half has
 469      the correctly rounded double value (in the only supported case of
 470      split values).  */
 471
 472   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 473                         fmt->exp_start, fmt->exp_len);
 474
 475   /* If the exponent indicates a NaN, we don't have information to
 476      decide what to do.  So we handle it like IEEE, except that we
 477      don't try to preserve the type of NaN.  FIXME.  */
 478   if ((unsigned long) exponent == fmt->exp_nan)
 479     {
 480       int nan = mant_bits_set (fmt, ufrom);
 481
 482       /* On certain systems (such as GNU/Linux), the use of the
 483          INFINITY macro below may generate a warning that can not be
 484          silenced due to a bug in GCC (PR preprocessor/11931).  The
 485          preprocessor fails to recognise the __extension__ keyword in
 486          conjunction with the GNU/C99 extension for hexadecimal
 487          floating point constants and will issue a warning when
 488          compiling with -pedantic.  */
 489       if (nan)
 490         dto = NAN;
 491       else
 492         dto = INFINITY;
 493
 494       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 495         dto = -dto;
 496
 497       *to = dto;
 498
 499       return;
 500     }
 501
 502   mant_bits_left = fmt->man_len;
 503   mant_off = fmt->man_start;
 504   dto = 0.0;
 505
 506   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 507
 508   /* Don't bias zero's, denorms or NaNs.  */
 509   if (!special_exponent)
 510     exponent -= fmt->exp_bias;
 511
 512   /* Build the result algebraically.  Might go infinite, underflow, etc;
 513      who cares. */
 514
 515   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 516      increment the exponent by one to account for the integer bit.  */
 517
 518   if (!special_exponent)
 519     {
 520       if (fmt->intbit == floatformat_intbit_no)
 521         dto = ldexp (1.0, exponent);
 522       else
 523         exponent++;
 524     }
 525
 526   while (mant_bits_left > 0)
 527     {
 528       mant_bits = min (mant_bits_left, 32);
 529
 530       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 531                          mant_off, mant_bits);
 532
 533       /* Handle denormalized numbers.  FIXME: What should we do for
 534          non-IEEE formats?  */
 535       if (special_exponent && exponent == 0 && mant != 0)
 536         dto += ldexp ((double)mant,
 537                       (- fmt->exp_bias
 538                        - mant_bits
 539                        - (mant_off - fmt->man_start)
 540                        + 1));
 541       else
 542         dto += ldexp ((double)mant, exponent - mant_bits);
 543       if (exponent != 0)
 544         exponent -= mant_bits;
 545       mant_off += mant_bits;
 546       mant_bits_left -= mant_bits;
 547     }
 548
 549   /* Negate it if negative.  */
 550   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 551     dto = -dto;
 552   *to = dto;
 553 }
 554 \f
 555 static void put_field (unsigned char *, enum floatformat_byteorders,
 556                        unsigned int,
 557                        unsigned int,
 558                        unsigned int,
 559                        unsigned long);
 560
 561 /* Set a field which starts at START and is LEN bits long.  DATA and
 562    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 563 static void
 564 put_field (unsigned char *data, enum floatformat_byteorders order,
 565            unsigned int total_len, unsigned int start, unsigned int len,
 566            unsigned long stuff_to_put)
 567 {
 568   unsigned int cur_byte;
 569   int lo_bit, hi_bit;
 570   int nextbyte = (order == floatformat_little) ? 1 : -1;
 571
 572   /* Start is in big-endian bit order!  Fix that first.  */
 573   start = total_len - (start + len);
 574
 575   /* Start at the least significant part of the field.  */
 576   if (order == floatformat_little)
 577     cur_byte = start / FLOATFORMAT_CHAR_BIT;
 578   else
 579     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
 580
 581   lo_bit = start % FLOATFORMAT_CHAR_BIT;
 582   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
 583
 584   do
 585     {
 586       unsigned char *byte_ptr = data + cur_byte;
 587       unsigned int bits = hi_bit - lo_bit;
 588       unsigned int mask = ((1 << bits) - 1) << lo_bit;
 589       *byte_ptr = (*byte_ptr & ~mask) | ((stuff_to_put << lo_bit) & mask);
 590       stuff_to_put >>= bits;
 591       len -= bits;
 592       cur_byte += nextbyte;
 593       lo_bit = 0;
 594       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
 595     }
 596   while (len != 0);
 597 }
 598
 599 /* The converse: convert the double *FROM to an extended float
 600    and store where TO points.  Neither FROM nor TO have any alignment
 601    restrictions.  */
 602
 603 void
 604 floatformat_from_double (const struct floatformat *fmt,
 605                          const double *from, void *to)
 606 {
 607   double dfrom;
 608   int exponent;
 609   double mant;
 610   unsigned int mant_bits, mant_off;
 611   int mant_bits_left;
 612   unsigned char *uto = (unsigned char *) to;
 613
 614   dfrom = *from;
 615   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 616
 617   /* Split values are not handled specially, since a bottom half of
 618      zero is correct for any value representable as double (in the
 619      only supported case of split values).  */
 620
 621   /* If negative, set the sign bit.  */
 622   if (dfrom < 0)
 623     {
 624       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 625       dfrom = -dfrom;
 626     }
 627
 628   if (dfrom == 0)
 629     {
 630       /* 0.0.  */
 631       return;
 632     }
 633
 634   if (dfrom != dfrom)
 635     {
 636       /* NaN.  */
 637       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 638                  fmt->exp_len, fmt->exp_nan);
 639       /* Be sure it's not infinity, but NaN value is irrelevant.  */
 640       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 641                  32, 1);
 642       return;
 643     }
 644
 645   if (dfrom + dfrom == dfrom)
 646     {
 647       /* This can only happen for an infinite value (or zero, which we
 648          already handled above).  */
 649       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 650                  fmt->exp_len, fmt->exp_nan);
 651       return;
 652     }
 653
 654   mant = frexp (dfrom, &exponent);
 655   if (exponent + fmt->exp_bias - 1 > 0)
 656     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 657                fmt->exp_len, exponent + fmt->exp_bias - 1);
 658   else
 659     {
 660       /* Handle a denormalized number.  FIXME: What should we do for
 661          non-IEEE formats?  */
 662       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 663                  fmt->exp_len, 0);
 664       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
 665     }
 666
 667   mant_bits_left = fmt->man_len;
 668   mant_off = fmt->man_start;
 669   while (mant_bits_left > 0)
 670     {
 671       unsigned long mant_long;
 672       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 673
 674       mant *= 4294967296.0;
 675       mant_long = (unsigned long)mant;
 676       mant -= mant_long;
 677
 678       /* If the integer bit is implicit, and we are not creating a
 679          denormalized number, then we need to discard it.  */
 680       if ((unsigned int) mant_bits_left == fmt->man_len
 681           && fmt->intbit == floatformat_intbit_no
 682           && exponent + fmt->exp_bias - 1 > 0)
 683         {
 684           mant_long &= 0x7fffffff;
 685           mant_bits -= 1;
 686         }
 687       else if (mant_bits < 32)
 688         {
 689           /* The bits we want are in the most significant MANT_BITS bits of
 690              mant_long.  Move them to the least significant.  */
 691           mant_long >>= 32 - mant_bits;
 692         }
 693
 694       put_field (uto, fmt->byteorder, fmt->totalsize,
 695                  mant_off, mant_bits, mant_long);
 696       mant_off += mant_bits;
 697       mant_bits_left -= mant_bits;
 698     }
 699 }
 700
 701 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
 702
 703 int
 704 floatformat_is_valid (const struct floatformat *fmt, const void *from)
 705 {
 706   return fmt->is_valid (fmt, from);
 707 }
 708
 709
 710 #ifdef IEEE_DEBUG
 711
 712 #include <stdio.h>
 713
 714 /* This is to be run on a host which uses IEEE floating point.  */
 715
 716 void
 717 ieee_test (double n)
 718 {
 719   double result;
 720
 721   floatformat_to_double (&floatformat_ieee_double_little, &n, &result);
 722   if ((n != result && (! isnan (n) || ! isnan (result)))
 723       || (n < 0 && result >= 0)
 724       || (n >= 0 && result < 0))
 725     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 726
 727   floatformat_from_double (&floatformat_ieee_double_little, &n, &result);
 728   if ((n != result && (! isnan (n) || ! isnan (result)))
 729       || (n < 0 && result >= 0)
 730       || (n >= 0 && result < 0))
 731     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 732
 733 #if 0
 734   {
 735     char exten[16];
 736
 737     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 738     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 739     if (n != result)
 740       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 741   }
 742 #endif
 743
 744 #if IEEE_DEBUG > 1
 745   /* This is to be run on a host which uses 68881 format.  */
 746   {
 747     long double ex = *(long double *)exten;
 748     if (ex != n)
 749       printf ("Differ(from vs. extended): %.20g\n", n);
 750   }
 751 #endif
 752 }
 753
 754 int
 755 main (void)
 756 {
 757   ieee_test (0.0);
 758   ieee_test (0.5);
 759   ieee_test (256.0);
 760   ieee_test (0.12345);
 761   ieee_test (234235.78907234);
 762   ieee_test (-512.0);
 763   ieee_test (-0.004321);
 764   ieee_test (1.2E-70);
 765   ieee_test (1.2E-316);
 766   ieee_test (4.9406564584124654E-324);
 767   ieee_test (- 4.9406564584124654E-324);
 768   ieee_test (- 0.0);
 769   ieee_test (- INFINITY);
 770   ieee_test (- NAN);
 771   ieee_test (INFINITY);
 772   ieee_test (NAN);
 773   return 0;
 774 }
 775 #endif