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_little"
  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 #ifdef HARRIS_FLOAT_FORMAT
  95   /* Harris uses raw format 128 bytes long, but the number is just an ieee
  96      double, and the last 64 bits are wasted. */
  97   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
  98   floatformat_intbit_no,
  99   "floatformat_m88110_ext(harris)"
 100 #else
 101   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
 102   floatformat_intbit_yes,
 103   "floatformat_m88110_ext"
 104 #endif /* HARRIS_FLOAT_FORMAT */
 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 \f
 114 static unsigned long get_field PARAMS ((unsigned char *,
 115                                         enum floatformat_byteorders,
 116                                         unsigned int,
 117                                         unsigned int,
 118                                         unsigned int));
 119
 120 /* Extract a field which starts at START and is LEN bytes long.  DATA and
 121    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 122 static unsigned long
 123 get_field (data, order, total_len, start, len)
 124      unsigned char *data;
 125      enum floatformat_byteorders order;
 126      unsigned int total_len;
 127      unsigned int start;
 128      unsigned int len;
 129 {
 130   unsigned long result;
 131   unsigned int cur_byte;
 132   int cur_bitshift;
 133
 134   /* Start at the least significant part of the field.  */
 135   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 136   if (order == floatformat_little)
 137     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 138   cur_bitshift =
 139     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 140   result = *(data + cur_byte) >> (-cur_bitshift);
 141   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 142   if (order == floatformat_little)
 143     ++cur_byte;
 144   else
 145     --cur_byte;
 146
 147   /* Move towards the most significant part of the field.  */
 148   while ((unsigned int) cur_bitshift < len)
 149     {
 150       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 151         /* This is the last byte; zero out the bits which are not part of
 152            this field.  */
 153         result |=
 154           (*(data + cur_byte) & ((1 << (len - cur_bitshift)) - 1))
 155             << cur_bitshift;
 156       else
 157         result |= *(data + cur_byte) << cur_bitshift;
 158       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 159       if (order == floatformat_little)
 160         ++cur_byte;
 161       else
 162         --cur_byte;
 163     }
 164   return result;
 165 }
 166
 167 #ifndef min
 168 #define min(a, b) ((a) < (b) ? (a) : (b))
 169 #endif
 170
 171 /* Convert from FMT to a double.
 172    FROM is the address of the extended float.
 173    Store the double in *TO.  */
 174
 175 void
 176 floatformat_to_double (fmt, from, to)
 177      const struct floatformat *fmt;
 178      char *from;
 179      double *to;
 180 {
 181   unsigned char *ufrom = (unsigned char *)from;
 182   double dto;
 183   long exponent;
 184   unsigned long mant;
 185   unsigned int mant_bits, mant_off;
 186   int mant_bits_left;
 187   int special_exponent;         /* It's a NaN, denorm or zero */
 188
 189   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 190                         fmt->exp_start, fmt->exp_len);
 191   /* Note that if exponent indicates a NaN, we can't really do anything useful
 192      (not knowing if the host has NaN's, or how to build one).  So it will
 193      end up as an infinity or something close; that is OK.  */
 194
 195   mant_bits_left = fmt->man_len;
 196   mant_off = fmt->man_start;
 197   dto = 0.0;
 198
 199   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
 200
 201   /* Don't bias zero's, denorms or NaNs.  */
 202   if (!special_exponent)
 203     exponent -= fmt->exp_bias;
 204
 205   /* Build the result algebraically.  Might go infinite, underflow, etc;
 206      who cares. */
 207
 208   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
 209      increment the exponent by one to account for the integer bit.  */
 210
 211   if (!special_exponent)
 212     {
 213       if (fmt->intbit == floatformat_intbit_no)
 214         dto = ldexp (1.0, exponent);
 215       else
 216         exponent++;
 217     }
 218
 219   while (mant_bits_left > 0)
 220     {
 221       mant_bits = min (mant_bits_left, 32);
 222
 223       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
 224                          mant_off, mant_bits);
 225
 226       dto += ldexp ((double)mant, exponent - mant_bits);
 227       exponent -= mant_bits;
 228       mant_off += mant_bits;
 229       mant_bits_left -= mant_bits;
 230     }
 231
 232   /* Negate it if negative.  */
 233   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
 234     dto = -dto;
 235   *to = dto;
 236 }
 237 \f
 238 static void put_field PARAMS ((unsigned char *, enum floatformat_byteorders,
 239                                unsigned int,
 240                                unsigned int,
 241                                unsigned int,
 242                                unsigned long));
 243
 244 /* Set a field which starts at START and is LEN bytes long.  DATA and
 245    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
 246 static void
 247 put_field (data, order, total_len, start, len, stuff_to_put)
 248      unsigned char *data;
 249      enum floatformat_byteorders order;
 250      unsigned int total_len;
 251      unsigned int start;
 252      unsigned int len;
 253      unsigned long stuff_to_put;
 254 {
 255   unsigned int cur_byte;
 256   int cur_bitshift;
 257
 258   /* Start at the least significant part of the field.  */
 259   cur_byte = (start + len) / FLOATFORMAT_CHAR_BIT;
 260   if (order == floatformat_little)
 261     cur_byte = (total_len / FLOATFORMAT_CHAR_BIT) - cur_byte - 1;
 262   cur_bitshift =
 263     ((start + len) % FLOATFORMAT_CHAR_BIT) - FLOATFORMAT_CHAR_BIT;
 264   *(data + cur_byte) &=
 265     ~(((1 << ((start + len) % FLOATFORMAT_CHAR_BIT)) - 1) << (-cur_bitshift));
 266   *(data + cur_byte) |=
 267     (stuff_to_put & ((1 << FLOATFORMAT_CHAR_BIT) - 1)) << (-cur_bitshift);
 268   cur_bitshift += FLOATFORMAT_CHAR_BIT;
 269   if (order == floatformat_little)
 270     ++cur_byte;
 271   else
 272     --cur_byte;
 273
 274   /* Move towards the most significant part of the field.  */
 275   while ((unsigned int) cur_bitshift < len)
 276     {
 277       if (len - cur_bitshift < FLOATFORMAT_CHAR_BIT)
 278         {
 279           /* This is the last byte.  */
 280           *(data + cur_byte) &=
 281             ~((1 << (len - cur_bitshift)) - 1);
 282           *(data + cur_byte) |= (stuff_to_put >> cur_bitshift);
 283         }
 284       else
 285         *(data + cur_byte) = ((stuff_to_put >> cur_bitshift)
 286                               & ((1 << FLOATFORMAT_CHAR_BIT) - 1));
 287       cur_bitshift += FLOATFORMAT_CHAR_BIT;
 288       if (order == floatformat_little)
 289         ++cur_byte;
 290       else
 291         --cur_byte;
 292     }
 293 }
 294
 295 /* The converse: convert the double *FROM to an extended float
 296    and store where TO points.  Neither FROM nor TO have any alignment
 297    restrictions.  */
 298
 299 void
 300 floatformat_from_double (fmt, from, to)
 301      const struct floatformat *fmt;
 302      double *from;
 303      char *to;
 304 {
 305   double dfrom;
 306   int exponent;
 307   double mant;
 308   unsigned int mant_bits, mant_off;
 309   int mant_bits_left;
 310   unsigned char *uto = (unsigned char *)to;
 311
 312   memcpy (&dfrom, from, sizeof (dfrom));
 313   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
 314   if (dfrom == 0)
 315     return;                     /* Result is zero */
 316   if (dfrom != dfrom)
 317     {
 318       /* From is NaN */
 319       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
 320                  fmt->exp_len, fmt->exp_nan);
 321       /* Be sure it's not infinity, but NaN value is irrel */
 322       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
 323                  32, 1);
 324       return;
 325     }
 326
 327   /* If negative, set the sign bit.  */
 328   if (dfrom < 0)
 329     {
 330       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
 331       dfrom = -dfrom;
 332     }
 333
 334   /* How to tell an infinity from an ordinary number?  FIXME-someday */
 335
 336   mant = frexp (dfrom, &exponent);
 337   put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start, fmt->exp_len,
 338              exponent + fmt->exp_bias - 1);
 339
 340   mant_bits_left = fmt->man_len;
 341   mant_off = fmt->man_start;
 342   while (mant_bits_left > 0)
 343     {
 344       unsigned long mant_long;
 345       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
 346
 347       mant *= 4294967296.0;
 348       mant_long = (unsigned long)mant;
 349       mant -= mant_long;
 350
 351       /* If the integer bit is implicit, then we need to discard it.
 352          If we are discarding a zero, we should be (but are not) creating
 353          a denormalized number which means adjusting the exponent
 354          (I think).  */
 355       if ((unsigned int) mant_bits_left == fmt->man_len
 356           && fmt->intbit == floatformat_intbit_no)
 357         {
 358           mant_long &= 0x7fffffff;
 359           mant_bits -= 1;
 360         }
 361       else if (mant_bits < 32)
 362         {
 363           /* The bits we want are in the most significant MANT_BITS bits of
 364              mant_long.  Move them to the least significant.  */
 365           mant_long >>= 32 - mant_bits;
 366         }
 367
 368       put_field (uto, fmt->byteorder, fmt->totalsize,
 369                  mant_off, mant_bits, mant_long);
 370       mant_off += mant_bits;
 371       mant_bits_left -= mant_bits;
 372     }
 373 }
 374
 375
 376 #ifdef IEEE_DEBUG
 377
 378 /* This is to be run on a host which uses IEEE floating point.  */
 379
 380 void
 381 ieee_test (n)
 382      double n;
 383 {
 384   double result;
 385   char exten[16];
 386
 387   floatformat_to_double (&floatformat_ieee_double_big, &n, &result);
 388   if (n != result)
 389     printf ("Differ(to): %.20g -> %.20g\n", n, result);
 390   floatformat_from_double (&floatformat_ieee_double_big, &n, &result);
 391   if (n != result)
 392     printf ("Differ(from): %.20g -> %.20g\n", n, result);
 393
 394   floatformat_from_double (&floatformat_m68881_ext, &n, exten);
 395   floatformat_to_double (&floatformat_m68881_ext, exten, &result);
 396   if (n != result)
 397     printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
 398
 399 #if IEEE_DEBUG > 1
 400   /* This is to be run on a host which uses 68881 format.  */
 401   {
 402     long double ex = *(long double *)exten;
 403     if (ex != n)
 404       printf ("Differ(from vs. extended): %.20g\n", n);
 405   }
 406 #endif
 407 }
 408
 409 int
 410 main ()
 411 {
 412   ieee_test (0.5);
 413   ieee_test (256.0);
 414   ieee_test (0.12345);
 415   ieee_test (234235.78907234);
 416   ieee_test (-512.0);
 417   ieee_test (-0.004321);
 418   return 0;
 419 }
 420 #endif