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 =
 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"
 112 };
 113 const struct floatformat floatformat_arm_ext_big =
 114 {
 115   /* Bits 1 to 16 are unused.  */
 116   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 117   floatformat_intbit_yes,
 118   "floatformat_arm_ext_big"
 119 };
 120 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
 121 {
 122   /* Bits 1 to 16 are unused.  */
 123   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
 124   floatformat_intbit_yes,
 125   "floatformat_arm_ext_littlebyte_bigword"
 126 };
 127 const struct floatformat floatformat_ia64_spill_big =
 128 {
 129   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 130   floatformat_intbit_yes,
 131   "floatformat_ia64_spill_big"
 132 };
 133 const struct floatformat floatformat_ia64_spill_little =
 134 {
 135   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
 136   floatformat_intbit_yes,
 137   "floatformat_ia64_spill_little"
 138 };
 139 const struct floatformat floatformat_ia64_quad_big =
 140 {
 141   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 142   floatformat_intbit_no,
 143   "floatformat_ia64_quad_big"
 144 };
 145 const struct floatformat floatformat_ia64_quad_little =
 146 {
 147   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
 148   floatformat_intbit_no,
 149   "floatformat_ia64_quad_little"
 150 };
 151 \f
 152 static unsigned long get_field PARAMS ((unsigned char *,
 153                                         enum floatformat_byteorders,
 154                                         unsigned int,
 155                                         unsigned int,
 156                                         unsigned int));
 157
 158 /* Extract a field which starts at START and is LEN bytes long.  DATA and
 159    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 160 static unsigned long
 161 get_field (data, order, total_len, start, len)
 162      unsigned char *data;
 163      enum floatformat_byteorders order;
 164      unsigned int total_len;
 165      unsigned int start;
 166      unsigned int len;
 167 {
 168   unsigned long result;
 169   unsigned int cur_byte;
 170   int cur_bitshift;
 171
 172   /* Start at the least significant part of the field.  */
 173   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 174   if (order == floatformat_little)
 175     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 176   cur_bitshift =
 177     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 178   result = *(data + cur_byte) >> (-cur_bitshift);
 179   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 180   if (order == floatformat_little)
 181     ++cur_byte;
 182   else
 183     --cur_byte;
 184
 185   /* Move towards the most significant part of the field.  */
 186   while ((unsigned int) cur_bitshift < len)
 187     {
 188       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 189         /* This is the last byte; zero out the bits which are not part of
 190            this field.  */
 191         result |=
 192           (*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
 193             << cur_bitshift;
 194       else
 195         result |= *(data + cur_byte) << cur_bitshift;
 196       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 197       if (order == floatformat_little)
 198         ++cur_byte;
 199       else
 200         --cur_byte;
 201     }
 202   return result;
 203 }
 204
 205 #ifndef min
 206 #define min(a, b) ((a) < (b) ? (a) : (b))
 207 #endif
 208
 209 /* Convert from FMT to a double.
 210    FROM is the address of the extended float.
 211    Store the double in *TO.  */
 212
 213 void
 214 floatformat_to_double (fmt, from, to)
 215      const struct floatformat *fmt;
 216      char *from;
 217      double *to;
 218 {
 219   unsigned char *ufrom = (unsigned char *)from;
 220   double dto;
 221   long exponent;
 222   unsigned long mant;
 223   unsigned int mant_bits, mant_off;
 224   int mant_bits_left;
 225   int special_exponent;         /* It's a NaN, denorm or zero */
 226
 227   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 228                         fmt->exp_start, fmt->exp_len);
 229   /* Note that if exponent indicates a NaN, we can't really do anything useful
 230      (not knowing if the host has NaN's, or how to build one).  So it will
 231      end up as an infinity or something close; that is OK.  */
 232
 233   mant_bits_left = fmt->man_len;
 234   mant_off = fmt->man_start;
 235   dto = 0.0;
 236
 237   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 238
 239   /* Don't bias zero's, denorms or NaNs.  */
 240   if (!special_exponent)
 241     exponent -= fmt->exp_bias;
 242
 243   /* Build the result algebraically.  Might go infinite, underflow, etc;
 244      who cares. */
 245
 246   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 247      increment the exponent by one to account for the integer bit.  */
 248
 249   if (!special_exponent)
 250     {
 251       if (fmt->intbit == floatformat_intbit_no)
 252         dto = ldexp (1.0, exponent);
 253       else
 254         exponent++;
 255     }
 256
 257   while (mant_bits_left > 0)
 258     {
 259       mant_bits = min (mant_bits_left, 32);
 260
 261       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 262                          mant_off, mant_bits);
 263
 264       dto += ldexp ((double)mant, exponent - mant_bits);
 265       exponent -= mant_bits;
 266       mant_off += mant_bits;
 267       mant_bits_left -= mant_bits;
 268     }
 269
 270   /* Negate it if negative.  */
 271   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 272     dto = -dto;
 273   *to = dto;
 274 }
 275 \f
 276 static void put_field PARAMS ((unsigned char *, enum floatformat_byteorders,
 277                                unsigned int,
 278                                unsigned int,
 279                                unsigned int,
 280                                unsigned long));
 281
 282 /* Set a field which starts at START and is LEN bytes long.  DATA and
 283    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 284 static void
 285 put_field (data, order, total_len, start, len, stuff_to_put)
 286      unsigned char *data;
 287      enum floatformat_byteorders order;
 288      unsigned int total_len;
 289      unsigned int start;
 290      unsigned int len;
 291      unsigned long stuff_to_put;
 292 {
 293   unsigned int cur_byte;
 294   int cur_bitshift;
 295
 296   /* Start at the least significant part of the field.  */
 297   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 298   if (order == floatformat_little)
 299     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 300   cur_bitshift =
 301     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 302   *(data + cur_byte) &=
 303     ~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
 304   *(data + cur_byte) |=
 305     (stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
 306   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 307   if (order == floatformat_little)
 308     ++cur_byte;
 309   else
 310     --cur_byte;
 311
 312   /* Move towards the most significant part of the field.  */
 313   while ((unsigned int) cur_bitshift < len)
 314     {
 315       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 316         {
 317           /* This is the last byte.  */
 318           *(data + cur_byte) &=
 319             ~((1 << (len - cur_bitshift)) - 1);
 320           *(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
 321         }
 322       else
 323         *(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
 324                               & ((1 << FLOATFORMAT_CHAR_BIT) - 1));
 325       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 326       if (order == floatformat_little)
 327         ++cur_byte;
 328       else
 329         --cur_byte;
 330     }
 331 }
 332
 333 /* The converse: convert the double *FROM to an extended float
 334    and store where TO points.  Neither FROM nor TO have any alignment
 335    restrictions.  */
 336
 337 void
 338 floatformat_from_double (fmt, from, to)
 339      const struct floatformat *fmt;
 340      double *from;
 341      char *to;
 342 {
 343   double dfrom;
 344   int exponent;
 345   double mant;
 346   unsigned int mant_bits, mant_off;
 347   int mant_bits_left;
 348   unsigned char *uto = (unsigned char *)to;
 349
 350   memcpy (&dfrom, from, sizeof (dfrom));
 351   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 352   if (dfrom == 0)
 353     return;                     /* Result is zero */
 354   if (dfrom != dfrom)
 355     {
 356       /* From is NaN */
 357       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 358                  fmt->exp_len, fmt->exp_nan);
 359       /* Be sure it's not infinity, but NaN value is irrel */
 360       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 361                  32, 1);
 362       return;
 363     }
 364
 365   /* If negative, set the sign bit.  */
 366   if (dfrom < 0)
 367     {
 368       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 369       dfrom = -dfrom;
 370     }
 371
 372   /* How to tell an infinity from an ordinary number?  FIXME-someday */
 373
 374   mant = frexp (dfrom, &exponent);
 375   put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start, fmt->exp_len,
 376              exponent + fmt->exp_bias - 1);
 377
 378   mant_bits_left = fmt->man_len;
 379   mant_off = fmt->man_start;
 380   while (mant_bits_left > 0)
 381     {
 382       unsigned long mant_long;
 383       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 384
 385       mant *= 4294967296.0;
 386       mant_long = (unsigned long)mant;
 387       mant -= mant_long;
 388
 389       /* If the integer bit is implicit, then we need to discard it.
 390          If we are discarding a zero, we should be (but are not) creating
 391          a denormalized number which means adjusting the exponent
 392          (I think).  */
 393       if ((unsigned int) mant_bits_left == fmt->man_len
 394           && fmt->intbit == floatformat_intbit_no)
 395         {
 396           mant_long &= 0x7fffffff;
 397           mant_bits -= 1;
 398         }
 399       else if (mant_bits < 32)
 400         {
 401           /* The bits we want are in the most significant MANT_BITS bits of
 402              mant_long.  Move them to the least significant.  */
 403           mant_long >>= 32 - mant_bits;
 404         }
 405
 406       put_field (uto, fmt->byteorder, fmt->totalsize,
 407                  mant_off, mant_bits, mant_long);
 408       mant_off += mant_bits;
 409       mant_bits_left -= mant_bits;
 410     }
 411 }
 412
 413
 414 #ifdef IEEE_DEBUG
 415
 416 /* This is to be run on a host which uses IEEE floating point.  */
 417
 418 void
 419 ieee_test (n)
 420      double n;
 421 {
 422   double result;
 423   char exten[16];
 424
 425   floatformat_to_double (&floatformat_ieee_double_big, &n, &result);
 426   if (n != result)
 427     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 428   floatformat_from_double (&floatformat_ieee_double_big, &n, &result);
 429   if (n != result)
 430     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 431
 432   floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 433   floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 434   if (n != result)
 435     printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 436
 437 #if IEEE_DEBUG > 1
 438   /* This is to be run on a host which uses 68881 format.  */
 439   {
 440     long double ex = *(long double *)exten;
 441     if (ex != n)
 442       printf ("Differ(from vs. extended): %.20g\n", n);
 443   }
 444 #endif
 445 }
 446
 447 int
 448 main ()
 449 {
 450   ieee_test (0.5);
 451   ieee_test (256.0);
 452   ieee_test (0.12345);
 453   ieee_test (234235.78907234);
 454   ieee_test (-512.0);
 455   ieee_test (-0.004321);
 456   return 0;
 457 }
 458 #endif