libiberty/floatformat.c

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