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