libiberty/floatformat.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright (C) 1991, 1994, 1999, 2000 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 #include "floatformat.h"
  21 #include <math.h>               /* ldexp */
  22 #ifdef __STDC__
  23 #include <stddef.h>
  24 extern void *memcpy (void *s1, const void *s2, size_t n);
  25 extern void *memset (void *s, int c, size_t n);
  26 #else
  27 extern char *memcpy ();
  28 extern char *memset ();
  29 #endif
  30
  31 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
  32    going to bother with trying to muck around with whether it is defined in
  33    a system header, what we do if not, etc.  */
  34 #define FLOATFORMAT_CHAR_BIT 8
  35
  36 /* floatformats for IEEE single and double, big and little endian.  */
  37 const struct floatformat floatformat_ieee_single_big =
  38 {
  39   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
  40   floatformat_intbit_no,
  41   "floatformat_ieee_single_big"
  42 };
  43 const struct floatformat floatformat_ieee_single_little =
  44 {
  45   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
  46   floatformat_intbit_no,
  47   "floatformat_ieee_single_little"
  48 };
  49 const struct floatformat floatformat_ieee_double_big =
  50 {
  51   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
  52   floatformat_intbit_no,
  53   "floatformat_ieee_double_big"
  54 };
  55 const struct floatformat floatformat_ieee_double_little =
  56 {
  57   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
  58   floatformat_intbit_no,
  59   "floatformat_ieee_double_little"
  60 };
  61
  62 /* floatformat for IEEE double, little endian byte order, with big endian word
  63    ordering, as on the ARM.  */
  64
  65 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
  66 {
  67   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
  68   floatformat_intbit_no,
  69   "floatformat_ieee_double_littlebyte_bigword"
  70 };
  71
  72 const struct floatformat floatformat_i387_ext =
  73 {
  74   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
  75   floatformat_intbit_yes,
  76   "floatformat_i387_ext"
  77 };
  78 const struct floatformat floatformat_m68881_ext =
  79 {
  80   /* Note that the bits from 16 to 31 are unused.  */
  81   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
  82   floatformat_intbit_yes,
  83   "floatformat_m68881_ext"
  84 };
  85 const struct floatformat floatformat_i960_ext =
  86 {
  87   /* Note that the bits from 0 to 15 are unused.  */
  88   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
  89   floatformat_intbit_yes,
  90   "floatformat_i960_ext"
  91 };
  92 const struct floatformat floatformat_m88110_ext =
  93 {
  94   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
  95   floatformat_intbit_yes,
  96   "floatformat_m88110_ext"
  97 };
  98 const struct floatformat floatformat_m88110_harris_ext =
  99 {
 100   /* Harris uses raw format 128 bytes long, but the number is just an ieee
 101      double, and the last 64 bits are wasted. */
 102   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
 103   floatformat_intbit_no,
 104   "floatformat_m88110_ext_harris"
 105 };
 106 const struct floatformat floatformat_arm_ext_big =
 107 {
 108   /* Bits 1 to 16 are unused.  */
 109   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 110   floatformat_intbit_yes,
 111   "floatformat_arm_ext_big"
 112 };
 113 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 114 {
 115   /* Bits 1 to 16 are unused.  */
 116   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 117   floatformat_intbit_yes,
 118   "floatformat_arm_ext_littlebyte_bigword"
 119 };
 120 const struct floatformat floatformat_ia64_spill_big =
 121 {
 122   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 123   floatformat_intbit_yes,
 124   "floatformat_ia64_spill_big"
 125 };
 126 const struct floatformat floatformat_ia64_spill_little =
 127 {
 128   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 129   floatformat_intbit_yes,
 130   "floatformat_ia64_spill_little"
 131 };
 132 const struct floatformat floatformat_ia64_quad_big =
 133 {
 134   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 135   floatformat_intbit_no,
 136   "floatformat_ia64_quad_big"
 137 };
 138 const struct floatformat floatformat_ia64_quad_little =
 139 {
 140   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 141   floatformat_intbit_no,
 142   "floatformat_ia64_quad_little"
 143 };
 144 \f
 145 static unsigned long get_field PARAMS ((unsigned char *,
 146                                         enum floatformat_byteorders,
 147                                         unsigned int,
 148                                         unsigned int,
 149                                         unsigned int));
 150
 151 /* Extract a field which starts at START and is LEN bytes long.  DATA and
 152    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 153 static unsigned long
 154 get_field (data, order, total_len, start, len)
 155      unsigned char *data;
 156      enum floatformat_byteorders order;
 157      unsigned int total_len;
 158      unsigned int start;
 159      unsigned int len;
 160 {
 161   unsigned long result;
 162   unsigned int cur_byte;
 163   int cur_bitshift;
 164
 165   /* Start at the least significant part of the field.  */
 166   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 167   if (order == floatformat_little)
 168     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 169   cur_bitshift =
 170     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 171   result = *(data + cur_byte) >> (-cur_bitshift);
 172   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 173   if (order == floatformat_little)
 174     ++cur_byte;
 175   else
 176     --cur_byte;
 177
 178   /* Move towards the most significant part of the field.  */
 179   while ((unsigned int) cur_bitshift < len)
 180     {
 181       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 182         /* This is the last byte; zero out the bits which are not part of
 183            this field.  */
 184         result |=
 185           (*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
 186             << cur_bitshift;
 187       else
 188         result |= *(data + cur_byte) << cur_bitshift;
 189       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 190       if (order == floatformat_little)
 191         ++cur_byte;
 192       else
 193         --cur_byte;
 194     }
 195   return result;
 196 }
 197
 198 #ifndef min
 199 #define min(a, b) ((a) < (b) ? (a) : (b))
 200 #endif
 201
 202 /* Convert from FMT to a double.
 203    FROM is the address of the extended float.
 204    Store the double in *TO.  */
 205
 206 void
 207 floatformat_to_double (fmt, from, to)
 208      const struct floatformat *fmt;
 209      char *from;
 210      double *to;
 211 {
 212   unsigned char *ufrom = (unsigned char *)from;
 213   double dto;
 214   long exponent;
 215   unsigned long mant;
 216   unsigned int mant_bits, mant_off;
 217   int mant_bits_left;
 218   int special_exponent;         /* It's a NaN, denorm or zero */
 219
 220   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 221                         fmt->exp_start, fmt->exp_len);
 222   /* Note that if exponent indicates a NaN, we can't really do anything useful
 223      (not knowing if the host has NaN's, or how to build one).  So it will
 224      end up as an infinity or something close; that is OK.  */
 225
 226   mant_bits_left = fmt->man_len;
 227   mant_off = fmt->man_start;
 228   dto = 0.0;
 229
 230   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 231
 232   /* Don't bias zero's, denorms or NaNs.  */
 233   if (!special_exponent)
 234     exponent -= fmt->exp_bias;
 235
 236   /* Build the result algebraically.  Might go infinite, underflow, etc;
 237      who cares. */
 238
 239   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 240      increment the exponent by one to account for the integer bit.  */
 241
 242   if (!special_exponent)
 243     {
 244       if (fmt->intbit == floatformat_intbit_no)
 245         dto = ldexp (1.0, exponent);
 246       else
 247         exponent++;
 248     }
 249
 250   while (mant_bits_left > 0)
 251     {
 252       mant_bits = min (mant_bits_left, 32);
 253
 254       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 255                          mant_off, mant_bits);
 256
 257       dto += ldexp ((double)mant, exponent - mant_bits);
 258       exponent -= mant_bits;
 259       mant_off += mant_bits;
 260       mant_bits_left -= mant_bits;
 261     }
 262
 263   /* Negate it if negative.  */
 264   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 265     dto = -dto;
 266   *to = dto;
 267 }
 268 \f
 269 static void put_field PARAMS ((unsigned char *, enum floatformat_byteorders,
 270                                unsigned int,
 271                                unsigned int,
 272                                unsigned int,
 273                                unsigned long));
 274
 275 /* Set a field which starts at START and is LEN bytes long.  DATA and
 276    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 277 static void
 278 put_field (data, order, total_len, start, len, stuff_to_put)
 279      unsigned char *data;
 280      enum floatformat_byteorders order;
 281      unsigned int total_len;
 282      unsigned int start;
 283      unsigned int len;
 284      unsigned long stuff_to_put;
 285 {
 286   unsigned int cur_byte;
 287   int cur_bitshift;
 288
 289   /* Start at the least significant part of the field.  */
 290   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 291   if (order == floatformat_little)
 292     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 293   cur_bitshift =
 294     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 295   *(data + cur_byte) &=
 296     ~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
 297   *(data + cur_byte) |=
 298     (stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
 299   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 300   if (order == floatformat_little)
 301     ++cur_byte;
 302   else
 303     --cur_byte;
 304
 305   /* Move towards the most significant part of the field.  */
 306   while ((unsigned int) cur_bitshift < len)
 307     {
 308       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 309         {
 310           /* This is the last byte.  */
 311           *(data + cur_byte) &=
 312             ~((1 << (len - cur_bitshift)) - 1);
 313           *(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
 314         }
 315       else
 316         *(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
 317                               & ((1 << FLOATFORMAT_CHAR_BIT) - 1));
 318       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 319       if (order == floatformat_little)
 320         ++cur_byte;
 321       else
 322         --cur_byte;
 323     }
 324 }
 325
 326 /* The converse: convert the double *FROM to an extended float
 327    and store where TO points.  Neither FROM nor TO have any alignment
 328    restrictions.  */
 329
 330 void
 331 floatformat_from_double (fmt, from, to)
 332      const struct floatformat *fmt;
 333      double *from;
 334      char *to;
 335 {
 336   double dfrom;
 337   int exponent;
 338   double mant;
 339   unsigned int mant_bits, mant_off;
 340   int mant_bits_left;
 341   unsigned char *uto = (unsigned char *)to;
 342
 343   memcpy (&dfrom, from, sizeof (dfrom));
 344   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 345   if (dfrom == 0)
 346     return;                     /* Result is zero */
 347   if (dfrom != dfrom)
 348     {
 349       /* From is NaN */
 350       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 351                  fmt->exp_len, fmt->exp_nan);
 352       /* Be sure it's not infinity, but NaN value is irrel */
 353       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 354                  32, 1);
 355       return;
 356     }
 357
 358   /* If negative, set the sign bit.  */
 359   if (dfrom < 0)
 360     {
 361       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 362       dfrom = -dfrom;
 363     }
 364
 365   /* How to tell an infinity from an ordinary number?  FIXME-someday */
 366
 367   mant = frexp (dfrom, &exponent);
 368   put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start, fmt->exp_len,
 369              exponent + fmt->exp_bias - 1);
 370
 371   mant_bits_left = fmt->man_len;
 372   mant_off = fmt->man_start;
 373   while (mant_bits_left > 0)
 374     {
 375       unsigned long mant_long;
 376       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 377
 378       mant *= 4294967296.0;
 379       mant_long = (unsigned long)mant;
 380       mant -= mant_long;
 381
 382       /* If the integer bit is implicit, then we need to discard it.
 383          If we are discarding a zero, we should be (but are not) creating
 384          a denormalized number which means adjusting the exponent
 385          (I think).  */
 386       if ((unsigned int) mant_bits_left == fmt->man_len
 387           && fmt->intbit == floatformat_intbit_no)
 388         {
 389           mant_long &= 0x7fffffff;
 390           mant_bits -= 1;
 391         }
 392       else if (mant_bits < 32)
 393         {
 394           /* The bits we want are in the most significant MANT_BITS bits of
 395              mant_long.  Move them to the least significant.  */
 396           mant_long >>= 32 - mant_bits;
 397         }
 398
 399       put_field (uto, fmt->byteorder, fmt->totalsize,
 400                  mant_off, mant_bits, mant_long);
 401       mant_off += mant_bits;
 402       mant_bits_left -= mant_bits;
 403     }
 404 }
 405
 406
 407 #ifdef IEEE_DEBUG
 408
 409 /* This is to be run on a host which uses IEEE floating point.  */
 410
 411 void
 412 ieee_test (n)
 413      double n;
 414 {
 415   double result;
 416   char exten[16];
 417
 418   floatformat_to_double (&floatformat_ieee_double_big, &n, &result);
 419   if (n != result)
 420     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 421   floatformat_from_double (&floatformat_ieee_double_big, &n, &result);
 422   if (n != result)
 423     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 424
 425   floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 426   floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 427   if (n != result)
 428     printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 429
 430 #if IEEE_DEBUG > 1
 431   /* This is to be run on a host which uses 68881 format.  */
 432   {
 433     long double ex = *(long double *)exten;
 434     if (ex != n)
 435       printf ("Differ(from vs. extended): %.20g\n", n);
 436   }
 437 #endif
 438 }
 439
 440 int
 441 main ()
 442 {
 443   ieee_test (0.5);
 444   ieee_test (256.0);
 445   ieee_test (0.12345);
 446   ieee_test (234235.78907234);
 447   ieee_test (-512.0);
 448   ieee_test (-0.004321);
 449   return 0;
 450 }
 451 #endif