libiberty/floatformat.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright (C) 1991, 1994, 1999, 2000, 2003 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., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  19
  20 /* This is needed to pick up the NAN macro on some systems.  */
  21 #define _GNU_SOURCE
  22
  23 #ifdef HAVE_CONFIG_H
  24 #include "config.h"
  25 #endif
  26
  27 #include <math.h>
  28
  29 #ifdef HAVE_STRING_H
  30 #include <string.h>
  31 #endif
  32
  33 #include "ansidecl.h"
  34 #include "libiberty.h"
  35 #include "floatformat.h"
  36
  37 #ifndef INFINITY
  38 #ifdef HUGE_VAL
  39 #define INFINITY HUGE_VAL
  40 #else
  41 #define INFINITY (1.0 / 0.0)
  42 #endif
  43 #endif
  44
  45 #ifndef NAN
  46 #define NAN (0.0 / 0.0)
  47 #endif
  48
  49 static unsigned long get_field (const unsigned char *,
  50                                 enum floatformat_byteorders,
  51                                 unsigned int,
  52                                 unsigned int,
  53                                 unsigned int);
  54 static int floatformat_always_valid (const struct floatformat *fmt,
  55                                      const char *from);
  56
  57 static int
  58 floatformat_always_valid (const struct floatformat *fmt ATTRIBUTE_UNUSED,
  59                           const char *from ATTRIBUTE_UNUSED)
  60 {
  61   return 1;
  62 }
  63
  64 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
  65    going to bother with trying to muck around with whether it is defined in
  66    a system header, what we do if not, etc.  */
  67 #define FLOATFORMAT_CHAR_BIT 8
  68
  69 /* floatformats for IEEE single and double, big and little endian.  */
  70 const struct floatformat floatformat_ieee_single_big =
  71 {
  72   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
  73   floatformat_intbit_no,
  74   "floatformat_ieee_single_big",
  75   floatformat_always_valid
  76 };
  77 const struct floatformat floatformat_ieee_single_little =
  78 {
  79   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
  80   floatformat_intbit_no,
  81   "floatformat_ieee_single_little",
  82   floatformat_always_valid
  83 };
  84 const struct floatformat floatformat_ieee_double_big =
  85 {
  86   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
  87   floatformat_intbit_no,
  88   "floatformat_ieee_double_big",
  89   floatformat_always_valid
  90 };
  91 const struct floatformat floatformat_ieee_double_little =
  92 {
  93   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
  94   floatformat_intbit_no,
  95   "floatformat_ieee_double_little",
  96   floatformat_always_valid
  97 };
  98
  99 /* floatformat for IEEE double, little endian byte order, with big endian word
 100    ordering, as on the ARM.  */
 101
 102 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
 103 {
 104   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
 105   floatformat_intbit_no,
 106   "floatformat_ieee_double_littlebyte_bigword",
 107   floatformat_always_valid
 108 };
 109
 110 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt, const char *from);
 111
 112 static int
 113 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const char *from)
 114 {
 115   /* In the i387 double-extended format, if the exponent is all ones,
 116      then the integer bit must be set.  If the exponent is neither 0
 117      nor ~0, the intbit must also be set.  Only if the exponent is
 118      zero can it be zero, and then it must be zero.  */
 119   unsigned long exponent, int_bit;
 120   const unsigned char *ufrom = (const unsigned char *) from;
 121
 122   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 123                         fmt->exp_start, fmt->exp_len);
 124   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 125                        fmt->man_start, 1);
 126
 127   if ((exponent == 0) != (int_bit == 0))
 128     return 0;
 129   else
 130     return 1;
 131 }
 132
 133 const struct floatformat floatformat_i387_ext =
 134 {
 135   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 136   floatformat_intbit_yes,
 137   "floatformat_i387_ext",
 138   floatformat_i387_ext_is_valid
 139 };
 140 const struct floatformat floatformat_m68881_ext =
 141 {
 142   /* Note that the bits from 16 to 31 are unused.  */
 143   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
 144   floatformat_intbit_yes,
 145   "floatformat_m68881_ext",
 146   floatformat_always_valid
 147 };
 148 const struct floatformat floatformat_i960_ext =
 149 {
 150   /* Note that the bits from 0 to 15 are unused.  */
 151   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
 152   floatformat_intbit_yes,
 153   "floatformat_i960_ext",
 154   floatformat_always_valid
 155 };
 156 const struct floatformat floatformat_m88110_ext =
 157 {
 158   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 159   floatformat_intbit_yes,
 160   "floatformat_m88110_ext",
 161   floatformat_always_valid
 162 };
 163 const struct floatformat floatformat_m88110_harris_ext =
 164 {
 165   /* Harris uses raw format 128 bytes long, but the number is just an ieee
 166      double, and the last 64 bits are wasted. */
 167   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
 168   floatformat_intbit_no,
 169   "floatformat_m88110_ext_harris",
 170   floatformat_always_valid
 171 };
 172 const struct floatformat floatformat_arm_ext_big =
 173 {
 174   /* Bits 1 to 16 are unused.  */
 175   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 176   floatformat_intbit_yes,
 177   "floatformat_arm_ext_big",
 178   floatformat_always_valid
 179 };
 180 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 181 {
 182   /* Bits 1 to 16 are unused.  */
 183   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 184   floatformat_intbit_yes,
 185   "floatformat_arm_ext_littlebyte_bigword",
 186   floatformat_always_valid
 187 };
 188 const struct floatformat floatformat_ia64_spill_big =
 189 {
 190   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 191   floatformat_intbit_yes,
 192   "floatformat_ia64_spill_big",
 193   floatformat_always_valid
 194 };
 195 const struct floatformat floatformat_ia64_spill_little =
 196 {
 197   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 198   floatformat_intbit_yes,
 199   "floatformat_ia64_spill_little",
 200   floatformat_always_valid
 201 };
 202 const struct floatformat floatformat_ia64_quad_big =
 203 {
 204   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 205   floatformat_intbit_no,
 206   "floatformat_ia64_quad_big",
 207   floatformat_always_valid
 208 };
 209 const struct floatformat floatformat_ia64_quad_little =
 210 {
 211   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 212   floatformat_intbit_no,
 213   "floatformat_ia64_quad_little",
 214   floatformat_always_valid
 215 };
 216 \f
 217 /* Extract a field which starts at START and is LEN bits long.  DATA and
 218    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 219 static unsigned long
 220 get_field (const unsigned char *data, enum floatformat_byteorders order,
 221            unsigned int total_len, unsigned int start, unsigned int len)
 222 {
 223   unsigned long result;
 224   unsigned int cur_byte;
 225   int cur_bitshift;
 226
 227   /* Start at the least significant part of the field.  */
 228   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 229   if (order == floatformat_little)
 230     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 231   cur_bitshift =
 232     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 233   result = *(data + cur_byte) >> (-cur_bitshift);
 234   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 235   if (order == floatformat_little)
 236     ++cur_byte;
 237   else
 238     --cur_byte;
 239
 240   /* Move towards the most significant part of the field.  */
 241   while ((unsigned int) cur_bitshift < len)
 242     {
 243       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 244         /* This is the last byte; zero out the bits which are not part of
 245            this field.  */
 246         result |=
 247           (*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
 248             << cur_bitshift;
 249       else
 250         result |= *(data + cur_byte) << cur_bitshift;
 251       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 252       if (order == floatformat_little)
 253         ++cur_byte;
 254       else
 255         --cur_byte;
 256     }
 257   return result;
 258 }
 259
 260 #ifndef min
 261 #define min(a, b) ((a) < (b) ? (a) : (b))
 262 #endif
 263
 264 /* Convert from FMT to a double.
 265    FROM is the address of the extended float.
 266    Store the double in *TO.  */
 267
 268 void
 269 floatformat_to_double (const struct floatformat *fmt,
 270                        const char *from, double *to)
 271 {
 272   const unsigned char *ufrom = (const unsigned char *)from;
 273   double dto;
 274   long exponent;
 275   unsigned long mant;
 276   unsigned int mant_bits, mant_off;
 277   int mant_bits_left;
 278   int special_exponent;         /* It's a NaN, denorm or zero */
 279
 280   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 281                         fmt->exp_start, fmt->exp_len);
 282
 283   /* If the exponent indicates a NaN, we don't have information to
 284      decide what to do.  So we handle it like IEEE, except that we
 285      don't try to preserve the type of NaN.  FIXME.  */
 286   if ((unsigned long) exponent == fmt->exp_nan)
 287     {
 288       int nan;
 289
 290       mant_off = fmt->man_start;
 291       mant_bits_left = fmt->man_len;
 292       nan = 0;
 293       while (mant_bits_left > 0)
 294         {
 295           mant_bits = min (mant_bits_left, 32);
 296
 297           if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
 298                          mant_off, mant_bits) != 0)
 299             {
 300               /* This is a NaN.  */
 301               nan = 1;
 302               break;
 303             }
 304
 305           mant_off += mant_bits;
 306           mant_bits_left -= mant_bits;
 307         }
 308
 309       if (nan)
 310         dto = NAN;
 311       else
 312         dto = INFINITY;
 313
 314       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 315         dto = -dto;
 316
 317       *to = dto;
 318
 319       return;
 320     }
 321
 322   mant_bits_left = fmt->man_len;
 323   mant_off = fmt->man_start;
 324   dto = 0.0;
 325
 326   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 327
 328   /* Don't bias zero's, denorms or NaNs.  */
 329   if (!special_exponent)
 330     exponent -= fmt->exp_bias;
 331
 332   /* Build the result algebraically.  Might go infinite, underflow, etc;
 333      who cares. */
 334
 335   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 336      increment the exponent by one to account for the integer bit.  */
 337
 338   if (!special_exponent)
 339     {
 340       if (fmt->intbit == floatformat_intbit_no)
 341         dto = ldexp (1.0, exponent);
 342       else
 343         exponent++;
 344     }
 345
 346   while (mant_bits_left > 0)
 347     {
 348       mant_bits = min (mant_bits_left, 32);
 349
 350       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 351                          mant_off, mant_bits);
 352
 353       /* Handle denormalized numbers.  FIXME: What should we do for
 354          non-IEEE formats?  */
 355       if (exponent == 0 && mant != 0)
 356         dto += ldexp ((double)mant,
 357                       (- fmt->exp_bias
 358                        - mant_bits
 359                        - (mant_off - fmt->man_start)
 360                        + 1));
 361       else
 362         dto += ldexp ((double)mant, exponent - mant_bits);
 363       if (exponent != 0)
 364         exponent -= mant_bits;
 365       mant_off += mant_bits;
 366       mant_bits_left -= mant_bits;
 367     }
 368
 369   /* Negate it if negative.  */
 370   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 371     dto = -dto;
 372   *to = dto;
 373 }
 374 \f
 375 static void put_field (unsigned char *, enum floatformat_byteorders,
 376                        unsigned int,
 377                        unsigned int,
 378                        unsigned int,
 379                        unsigned long);
 380
 381 /* Set a field which starts at START and is LEN bits long.  DATA and
 382    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 383 static void
 384 put_field (unsigned char *data, enum floatformat_byteorders order,
 385            unsigned int total_len, unsigned int start, unsigned int len,
 386            unsigned long stuff_to_put)
 387 {
 388   unsigned int cur_byte;
 389   int cur_bitshift;
 390
 391   /* Start at the least significant part of the field.  */
 392   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 393   if (order == floatformat_little)
 394     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 395   cur_bitshift =
 396     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 397   *(data + cur_byte) &=
 398     ~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
 399   *(data + cur_byte) |=
 400     (stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
 401   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 402   if (order == floatformat_little)
 403     ++cur_byte;
 404   else
 405     --cur_byte;
 406
 407   /* Move towards the most significant part of the field.  */
 408   while ((unsigned int) cur_bitshift < len)
 409     {
 410       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 411         {
 412           /* This is the last byte.  */
 413           *(data + cur_byte) &=
 414             ~((1 << (len - cur_bitshift)) - 1);
 415           *(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
 416         }
 417       else
 418         *(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
 419                               & ((1 << FLOATFORMAT_CHAR_BIT) - 1));
 420       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 421       if (order == floatformat_little)
 422         ++cur_byte;
 423       else
 424         --cur_byte;
 425     }
 426 }
 427
 428 /* The converse: convert the double *FROM to an extended float
 429    and store where TO points.  Neither FROM nor TO have any alignment
 430    restrictions.  */
 431
 432 void
 433 floatformat_from_double (const struct floatformat *fmt,
 434                          const double *from, char *to)
 435 {
 436   double dfrom;
 437   int exponent;
 438   double mant;
 439   unsigned int mant_bits, mant_off;
 440   int mant_bits_left;
 441   unsigned char *uto = (unsigned char *)to;
 442
 443   dfrom = *from;
 444   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 445
 446   /* If negative, set the sign bit.  */
 447   if (dfrom < 0)
 448     {
 449       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 450       dfrom = -dfrom;
 451     }
 452
 453   if (dfrom == 0)
 454     {
 455       /* 0.0.  */
 456       return;
 457     }
 458
 459   if (dfrom != dfrom)
 460     {
 461       /* NaN.  */
 462       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 463                  fmt->exp_len, fmt->exp_nan);
 464       /* Be sure it's not infinity, but NaN value is irrelevant.  */
 465       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 466                  32, 1);
 467       return;
 468     }
 469
 470   if (dfrom + dfrom == dfrom)
 471     {
 472       /* This can only happen for an infinite value (or zero, which we
 473          already handled above).  */
 474       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 475                  fmt->exp_len, fmt->exp_nan);
 476       return;
 477     }
 478
 479   mant = frexp (dfrom, &exponent);
 480   if (exponent + fmt->exp_bias - 1 > 0)
 481     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 482                fmt->exp_len, exponent + fmt->exp_bias - 1);
 483   else
 484     {
 485       /* Handle a denormalized number.  FIXME: What should we do for
 486          non-IEEE formats?  */
 487       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 488                  fmt->exp_len, 0);
 489       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
 490     }
 491
 492   mant_bits_left = fmt->man_len;
 493   mant_off = fmt->man_start;
 494   while (mant_bits_left > 0)
 495     {
 496       unsigned long mant_long;
 497       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 498
 499       mant *= 4294967296.0;
 500       mant_long = (unsigned long)mant;
 501       mant -= mant_long;
 502
 503       /* If the integer bit is implicit, and we are not creating a
 504          denormalized number, then we need to discard it.  */
 505       if ((unsigned int) mant_bits_left == fmt->man_len
 506           && fmt->intbit == floatformat_intbit_no
 507           && exponent + fmt->exp_bias - 1 > 0)
 508         {
 509           mant_long &= 0x7fffffff;
 510           mant_bits -= 1;
 511         }
 512       else if (mant_bits < 32)
 513         {
 514           /* The bits we want are in the most significant MANT_BITS bits of
 515              mant_long.  Move them to the least significant.  */
 516           mant_long >>= 32 - mant_bits;
 517         }
 518
 519       put_field (uto, fmt->byteorder, fmt->totalsize,
 520                  mant_off, mant_bits, mant_long);
 521       mant_off += mant_bits;
 522       mant_bits_left -= mant_bits;
 523     }
 524 }
 525
 526 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
 527
 528 int
 529 floatformat_is_valid (const struct floatformat *fmt, const char *from)
 530 {
 531   return fmt->is_valid (fmt, from);
 532 }
 533
 534
 535 #ifdef IEEE_DEBUG
 536
 537 #include <stdio.h>
 538
 539 /* This is to be run on a host which uses IEEE floating point.  */
 540
 541 void
 542 ieee_test (double n)
 543 {
 544   double result;
 545
 546   floatformat_to_double (&floatformat_ieee_double_little, (char *) &n,
 547                          &result);
 548   if ((n != result && (! isnan (n) || ! isnan (result)))
 549       || (n < 0 && result >= 0)
 550       || (n >= 0 && result < 0))
 551     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 552
 553   floatformat_from_double (&floatformat_ieee_double_little, &n,
 554                            (char *) &result);
 555   if ((n != result && (! isnan (n) || ! isnan (result)))
 556       || (n < 0 && result >= 0)
 557       || (n >= 0 && result < 0))
 558     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 559
 560 #if 0
 561   {
 562     char exten[16];
 563
 564     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 565     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 566     if (n != result)
 567       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 568   }
 569 #endif
 570
 571 #if IEEE_DEBUG > 1
 572   /* This is to be run on a host which uses 68881 format.  */
 573   {
 574     long double ex = *(long double *)exten;
 575     if (ex != n)
 576       printf ("Differ(from vs. extended): %.20g\n", n);
 577   }
 578 #endif
 579 }
 580
 581 int
 582 main (void)
 583 {
 584   ieee_test (0.0);
 585   ieee_test (0.5);
 586   ieee_test (256.0);
 587   ieee_test (0.12345);
 588   ieee_test (234235.78907234);
 589   ieee_test (-512.0);
 590   ieee_test (-0.004321);
 591   ieee_test (1.2E-70);
 592   ieee_test (1.2E-316);
 593   ieee_test (4.9406564584124654E-324);
 594   ieee_test (- 4.9406564584124654E-324);
 595   ieee_test (- 0.0);
 596   ieee_test (- INFINITY);
 597   ieee_test (- NAN);
 598   ieee_test (INFINITY);
 599   ieee_test (NAN);
 600   return 0;
 601 }
 602 #endif