libiberty/floatformat.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright 1991, 1994, 1999, 2000, 2003, 2005
   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 #include "ansidecl.h"
  35 #include "libiberty.h"
  36 #include "floatformat.h"
  37
  38 #ifndef INFINITY
  39 #ifdef HUGE_VAL
  40 #define INFINITY HUGE_VAL
  41 #else
  42 #define INFINITY (1.0 / 0.0)
  43 #endif
  44 #endif
  45
  46 #ifndef NAN
  47 #define NAN (0.0 / 0.0)
  48 #endif
  49
  50 static unsigned long get_field (const unsigned char *,
  51                                 enum floatformat_byteorders,
  52                                 unsigned int,
  53                                 unsigned int,
  54                                 unsigned int);
  55 static int floatformat_always_valid (const struct floatformat *fmt,
  56                                      const void *from);
  57
  58 static int
  59 floatformat_always_valid (const struct floatformat *fmt ATTRIBUTE_UNUSED,
  60                           const void *from ATTRIBUTE_UNUSED)
  61 {
  62   return 1;
  63 }
  64
  65 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
  66    going to bother with trying to muck around with whether it is defined in
  67    a system header, what we do if not, etc.  */
  68 #define FLOATFORMAT_CHAR_BIT 8
  69
  70 /* floatformats for IEEE single and double, big and little endian.  */
  71 const struct floatformat floatformat_ieee_single_big =
  72 {
  73   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
  74   floatformat_intbit_no,
  75   "floatformat_ieee_single_big",
  76   floatformat_always_valid
  77 };
  78 const struct floatformat floatformat_ieee_single_little =
  79 {
  80   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
  81   floatformat_intbit_no,
  82   "floatformat_ieee_single_little",
  83   floatformat_always_valid
  84 };
  85 const struct floatformat floatformat_ieee_double_big =
  86 {
  87   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
  88   floatformat_intbit_no,
  89   "floatformat_ieee_double_big",
  90   floatformat_always_valid
  91 };
  92 const struct floatformat floatformat_ieee_double_little =
  93 {
  94   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
  95   floatformat_intbit_no,
  96   "floatformat_ieee_double_little",
  97   floatformat_always_valid
  98 };
  99
 100 /* floatformat for IEEE double, little endian byte order, with big endian word
 101    ordering, as on the ARM.  */
 102
 103 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
 104 {
 105   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
 106   floatformat_intbit_no,
 107   "floatformat_ieee_double_littlebyte_bigword",
 108   floatformat_always_valid
 109 };
 110
 111 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt,
 112                                           const void *from);
 113
 114 static int
 115 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const void *from)
 116 {
 117   /* In the i387 double-extended format, if the exponent is all ones,
 118      then the integer bit must be set.  If the exponent is neither 0
 119      nor ~0, the intbit must also be set.  Only if the exponent is
 120      zero can it be zero, and then it must be zero.  */
 121   unsigned long exponent, int_bit;
 122   const unsigned char *ufrom = from;
 123
 124   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 125                         fmt->exp_start, fmt->exp_len);
 126   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 127                        fmt->man_start, 1);
 128
 129   if ((exponent == 0) != (int_bit == 0))
 130     return 0;
 131   else
 132     return 1;
 133 }
 134
 135 const struct floatformat floatformat_i387_ext =
 136 {
 137   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 138   floatformat_intbit_yes,
 139   "floatformat_i387_ext",
 140   floatformat_i387_ext_is_valid
 141 };
 142 const struct floatformat floatformat_m68881_ext =
 143 {
 144   /* Note that the bits from 16 to 31 are unused.  */
 145   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
 146   floatformat_intbit_yes,
 147   "floatformat_m68881_ext",
 148   floatformat_always_valid
 149 };
 150 const struct floatformat floatformat_i960_ext =
 151 {
 152   /* Note that the bits from 0 to 15 are unused.  */
 153   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
 154   floatformat_intbit_yes,
 155   "floatformat_i960_ext",
 156   floatformat_always_valid
 157 };
 158 const struct floatformat floatformat_m88110_ext =
 159 {
 160   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 161   floatformat_intbit_yes,
 162   "floatformat_m88110_ext",
 163   floatformat_always_valid
 164 };
 165 const struct floatformat floatformat_m88110_harris_ext =
 166 {
 167   /* Harris uses raw format 128 bytes long, but the number is just an ieee
 168      double, and the last 64 bits are wasted. */
 169   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
 170   floatformat_intbit_no,
 171   "floatformat_m88110_ext_harris",
 172   floatformat_always_valid
 173 };
 174 const struct floatformat floatformat_arm_ext_big =
 175 {
 176   /* Bits 1 to 16 are unused.  */
 177   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 178   floatformat_intbit_yes,
 179   "floatformat_arm_ext_big",
 180   floatformat_always_valid
 181 };
 182 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 183 {
 184   /* Bits 1 to 16 are unused.  */
 185   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 186   floatformat_intbit_yes,
 187   "floatformat_arm_ext_littlebyte_bigword",
 188   floatformat_always_valid
 189 };
 190 const struct floatformat floatformat_ia64_spill_big =
 191 {
 192   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 193   floatformat_intbit_yes,
 194   "floatformat_ia64_spill_big",
 195   floatformat_always_valid
 196 };
 197 const struct floatformat floatformat_ia64_spill_little =
 198 {
 199   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 200   floatformat_intbit_yes,
 201   "floatformat_ia64_spill_little",
 202   floatformat_always_valid
 203 };
 204 const struct floatformat floatformat_ia64_quad_big =
 205 {
 206   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 207   floatformat_intbit_no,
 208   "floatformat_ia64_quad_big",
 209   floatformat_always_valid
 210 };
 211 const struct floatformat floatformat_ia64_quad_little =
 212 {
 213   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 214   floatformat_intbit_no,
 215   "floatformat_ia64_quad_little",
 216   floatformat_always_valid
 217 };
 218 \f
 219 /* Extract a field which starts at START and is LEN bits long.  DATA and
 220    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 221 static unsigned long
 222 get_field (const unsigned char *data, enum floatformat_byteorders order,
 223            unsigned int total_len, unsigned int start, unsigned int len)
 224 {
 225   unsigned long result;
 226   unsigned int cur_byte;
 227   int cur_bitshift;
 228
 229   /* Start at the least significant part of the field.  */
 230   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 231   if (order == floatformat_little)
 232     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 233   cur_bitshift =
 234     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 235   result = *(data + cur_byte) >> (-cur_bitshift);
 236   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 237   if (order == floatformat_little)
 238     ++cur_byte;
 239   else
 240     --cur_byte;
 241
 242   /* Move towards the most significant part of the field.  */
 243   while ((unsigned int) cur_bitshift < len)
 244     {
 245       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 246         /* This is the last byte; zero out the bits which are not part of
 247            this field.  */
 248         result |=
 249           (*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
 250             << cur_bitshift;
 251       else
 252         result |= *(data + cur_byte) << cur_bitshift;
 253       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 254       if (order == floatformat_little)
 255         ++cur_byte;
 256       else
 257         --cur_byte;
 258     }
 259   return result;
 260 }
 261
 262 #ifndef min
 263 #define min(a, b) ((a) < (b) ? (a) : (b))
 264 #endif
 265
 266 /* Convert from FMT to a double.
 267    FROM is the address of the extended float.
 268    Store the double in *TO.  */
 269
 270 void
 271 floatformat_to_double (const struct floatformat *fmt,
 272                        const void *from, double *to)
 273 {
 274   const unsigned char *ufrom = from;
 275   double dto;
 276   long exponent;
 277   unsigned long mant;
 278   unsigned int mant_bits, mant_off;
 279   int mant_bits_left;
 280   int special_exponent;         /* It's a NaN, denorm or zero */
 281
 282   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 283                         fmt->exp_start, fmt->exp_len);
 284
 285   /* If the exponent indicates a NaN, we don't have information to
 286      decide what to do.  So we handle it like IEEE, except that we
 287      don't try to preserve the type of NaN.  FIXME.  */
 288   if ((unsigned long) exponent == fmt->exp_nan)
 289     {
 290       int nan;
 291
 292       mant_off = fmt->man_start;
 293       mant_bits_left = fmt->man_len;
 294       nan = 0;
 295       while (mant_bits_left > 0)
 296         {
 297           mant_bits = min (mant_bits_left, 32);
 298
 299           if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
 300                          mant_off, mant_bits) != 0)
 301             {
 302               /* This is a NaN.  */
 303               nan = 1;
 304               break;
 305             }
 306
 307           mant_off += mant_bits;
 308           mant_bits_left -= mant_bits;
 309         }
 310
 311       /* On certain systems (such as GNU/Linux), the use of the
 312          INFINITY macro below may generate a warning that can not be
 313          silenced due to a bug in GCC (PR preprocessor/11931).  The
 314          preprocessor fails to recognise the __extension__ keyword in
 315          conjunction with the GNU/C99 extension for hexadecimal
 316          floating point constants and will issue a warning when
 317          compiling with -pedantic.  */
 318       if (nan)
 319         dto = NAN;
 320       else
 321         dto = INFINITY;
 322
 323       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 324         dto = -dto;
 325
 326       *to = dto;
 327
 328       return;
 329     }
 330
 331   mant_bits_left = fmt->man_len;
 332   mant_off = fmt->man_start;
 333   dto = 0.0;
 334
 335   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 336
 337   /* Don't bias zero's, denorms or NaNs.  */
 338   if (!special_exponent)
 339     exponent -= fmt->exp_bias;
 340
 341   /* Build the result algebraically.  Might go infinite, underflow, etc;
 342      who cares. */
 343
 344   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 345      increment the exponent by one to account for the integer bit.  */
 346
 347   if (!special_exponent)
 348     {
 349       if (fmt->intbit == floatformat_intbit_no)
 350         dto = ldexp (1.0, exponent);
 351       else
 352         exponent++;
 353     }
 354
 355   while (mant_bits_left > 0)
 356     {
 357       mant_bits = min (mant_bits_left, 32);
 358
 359       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 360                          mant_off, mant_bits);
 361
 362       /* Handle denormalized numbers.  FIXME: What should we do for
 363          non-IEEE formats?  */
 364       if (exponent == 0 && mant != 0)
 365         dto += ldexp ((double)mant,
 366                       (- fmt->exp_bias
 367                        - mant_bits
 368                        - (mant_off - fmt->man_start)
 369                        + 1));
 370       else
 371         dto += ldexp ((double)mant, exponent - mant_bits);
 372       if (exponent != 0)
 373         exponent -= mant_bits;
 374       mant_off += mant_bits;
 375       mant_bits_left -= mant_bits;
 376     }
 377
 378   /* Negate it if negative.  */
 379   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 380     dto = -dto;
 381   *to = dto;
 382 }
 383 \f
 384 static void put_field (unsigned char *, enum floatformat_byteorders,
 385                        unsigned int,
 386                        unsigned int,
 387                        unsigned int,
 388                        unsigned long);
 389
 390 /* Set a field which starts at START and is LEN bits long.  DATA and
 391    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 392 static void
 393 put_field (unsigned char *data, enum floatformat_byteorders order,
 394            unsigned int total_len, unsigned int start, unsigned int len,
 395            unsigned long stuff_to_put)
 396 {
 397   unsigned int cur_byte;
 398   int cur_bitshift;
 399
 400   /* Start at the least significant part of the field.  */
 401   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 402   if (order == floatformat_little)
 403     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 404   cur_bitshift =
 405     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 406   *(data + cur_byte) &=
 407     ~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
 408   *(data + cur_byte) |=
 409     (stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
 410   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 411   if (order == floatformat_little)
 412     ++cur_byte;
 413   else
 414     --cur_byte;
 415
 416   /* Move towards the most significant part of the field.  */
 417   while ((unsigned int) cur_bitshift < len)
 418     {
 419       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 420         {
 421           /* This is the last byte.  */
 422           *(data + cur_byte) &=
 423             ~((1 << (len - cur_bitshift)) - 1);
 424           *(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
 425         }
 426       else
 427         *(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
 428                               & ((1 << FLOATFORMAT_CHAR_BIT) - 1));
 429       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 430       if (order == floatformat_little)
 431         ++cur_byte;
 432       else
 433         --cur_byte;
 434     }
 435 }
 436
 437 /* The converse: convert the double *FROM to an extended float
 438    and store where TO points.  Neither FROM nor TO have any alignment
 439    restrictions.  */
 440
 441 void
 442 floatformat_from_double (const struct floatformat *fmt,
 443                          const double *from, void *to)
 444 {
 445   double dfrom;
 446   int exponent;
 447   double mant;
 448   unsigned int mant_bits, mant_off;
 449   int mant_bits_left;
 450   unsigned char *uto = to;
 451
 452   dfrom = *from;
 453   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 454
 455   /* If negative, set the sign bit.  */
 456   if (dfrom < 0)
 457     {
 458       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 459       dfrom = -dfrom;
 460     }
 461
 462   if (dfrom == 0)
 463     {
 464       /* 0.0.  */
 465       return;
 466     }
 467
 468   if (dfrom != dfrom)
 469     {
 470       /* NaN.  */
 471       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 472                  fmt->exp_len, fmt->exp_nan);
 473       /* Be sure it's not infinity, but NaN value is irrelevant.  */
 474       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 475                  32, 1);
 476       return;
 477     }
 478
 479   if (dfrom + dfrom == dfrom)
 480     {
 481       /* This can only happen for an infinite value (or zero, which we
 482          already handled above).  */
 483       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 484                  fmt->exp_len, fmt->exp_nan);
 485       return;
 486     }
 487
 488   mant = frexp (dfrom, &exponent);
 489   if (exponent + fmt->exp_bias - 1 > 0)
 490     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 491                fmt->exp_len, exponent + fmt->exp_bias - 1);
 492   else
 493     {
 494       /* Handle a denormalized number.  FIXME: What should we do for
 495          non-IEEE formats?  */
 496       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 497                  fmt->exp_len, 0);
 498       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
 499     }
 500
 501   mant_bits_left = fmt->man_len;
 502   mant_off = fmt->man_start;
 503   while (mant_bits_left > 0)
 504     {
 505       unsigned long mant_long;
 506       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 507
 508       mant *= 4294967296.0;
 509       mant_long = (unsigned long)mant;
 510       mant -= mant_long;
 511
 512       /* If the integer bit is implicit, and we are not creating a
 513          denormalized number, then we need to discard it.  */
 514       if ((unsigned int) mant_bits_left == fmt->man_len
 515           && fmt->intbit == floatformat_intbit_no
 516           && exponent + fmt->exp_bias - 1 > 0)
 517         {
 518           mant_long &= 0x7fffffff;
 519           mant_bits -= 1;
 520         }
 521       else if (mant_bits < 32)
 522         {
 523           /* The bits we want are in the most significant MANT_BITS bits of
 524              mant_long.  Move them to the least significant.  */
 525           mant_long >>= 32 - mant_bits;
 526         }
 527
 528       put_field (uto, fmt->byteorder, fmt->totalsize,
 529                  mant_off, mant_bits, mant_long);
 530       mant_off += mant_bits;
 531       mant_bits_left -= mant_bits;
 532     }
 533 }
 534
 535 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
 536
 537 int
 538 floatformat_is_valid (const struct floatformat *fmt, const void *from)
 539 {
 540   return fmt->is_valid (fmt, from);
 541 }
 542
 543
 544 #ifdef IEEE_DEBUG
 545
 546 #include <stdio.h>
 547
 548 /* This is to be run on a host which uses IEEE floating point.  */
 549
 550 void
 551 ieee_test (double n)
 552 {
 553   double result;
 554
 555   floatformat_to_double (&floatformat_ieee_double_little, &n, &result);
 556   if ((n != result && (! isnan (n) || ! isnan (result)))
 557       || (n < 0 && result >= 0)
 558       || (n >= 0 && result < 0))
 559     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 560
 561   floatformat_from_double (&floatformat_ieee_double_little, &n, &result);
 562   if ((n != result && (! isnan (n) || ! isnan (result)))
 563       || (n < 0 && result >= 0)
 564       || (n >= 0 && result < 0))
 565     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 566
 567 #if 0
 568   {
 569     char exten[16];
 570
 571     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 572     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 573     if (n != result)
 574       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 575   }
 576 #endif
 577
 578 #if IEEE_DEBUG > 1
 579   /* This is to be run on a host which uses 68881 format.  */
 580   {
 581     long double ex = *(long double *)exten;
 582     if (ex != n)
 583       printf ("Differ(from vs. extended): %.20g\n", n);
 584   }
 585 #endif
 586 }
 587
 588 int
 589 main (void)
 590 {
 591   ieee_test (0.0);
 592   ieee_test (0.5);
 593   ieee_test (256.0);
 594   ieee_test (0.12345);
 595   ieee_test (234235.78907234);
 596   ieee_test (-512.0);
 597   ieee_test (-0.004321);
 598   ieee_test (1.2E-70);
 599   ieee_test (1.2E-316);
 600   ieee_test (4.9406564584124654E-324);
 601   ieee_test (- 4.9406564584124654E-324);
 602   ieee_test (- 0.0);
 603   ieee_test (- INFINITY);
 604   ieee_test (- NAN);
 605   ieee_test (INFINITY);
 606   ieee_test (NAN);
 607   return 0;
 608 }
 609 #endif