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floatformat.c revision 1.1
      1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
      2    Copyright 1991, 1994, 1999, 2000, 2003, 2005, 2006
      3    Free Software Foundation, Inc.
      4 
      5 This file is part of GDB.
      6 
      7 This program is free software; you can redistribute it and/or modify
      8 it under the terms of the GNU General Public License as published by
      9 the Free Software Foundation; either version 2 of the License, or
     10 (at your option) any later version.
     11 
     12 This program is distributed in the hope that it will be useful,
     13 but WITHOUT ANY WARRANTY; without even the implied warranty of
     14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     15 GNU General Public License for more details.
     16 
     17 You should have received a copy of the GNU General Public License
     18 along with this program; if not, write to the Free Software
     19 Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */
     20 
     21 /* This is needed to pick up the NAN macro on some systems.  */
     22 #define _GNU_SOURCE
     23 
     24 #ifdef HAVE_CONFIG_H
     25 #include "config.h"
     26 #endif
     27 
     28 #include <math.h>
     29 
     30 #ifdef HAVE_STRING_H
     31 #include <string.h>
     32 #endif
     33 
     34 /* On some platforms, <float.h> provides DBL_QNAN.  */
     35 #ifdef STDC_HEADERS
     36 #include <float.h>
     37 #endif
     38 
     39 #include "ansidecl.h"
     40 #include "libiberty.h"
     41 #include "floatformat.h"
     42 
     43 #ifndef INFINITY
     44 #ifdef HUGE_VAL
     45 #define INFINITY HUGE_VAL
     46 #else
     47 #define INFINITY (1.0 / 0.0)
     48 #endif
     49 #endif
     50 
     51 #ifndef NAN
     52 #ifdef DBL_QNAN
     53 #define NAN DBL_QNAN
     54 #else
     55 #define NAN (0.0 / 0.0)
     56 #endif
     57 #endif
     58 
     59 static int mant_bits_set (const struct floatformat *, const unsigned char *);
     60 static unsigned long get_field (const unsigned char *,
     61                                 enum floatformat_byteorders,
     62                                 unsigned int,
     63                                 unsigned int,
     64                                 unsigned int);
     65 static int floatformat_always_valid (const struct floatformat *fmt,
     66                                      const void *from);
     67 
     68 static int
     69 floatformat_always_valid (const struct floatformat *fmt ATTRIBUTE_UNUSED,
     70                           const void *from ATTRIBUTE_UNUSED)
     71 {
     72   return 1;
     73 }
     74 
     75 /* The odds that CHAR_BIT will be anything but 8 are low enough that I'm not
     76    going to bother with trying to muck around with whether it is defined in
     77    a system header, what we do if not, etc.  */
     78 #define FLOATFORMAT_CHAR_BIT 8
     79 
     80 /* floatformats for IEEE single and double, big and little endian.  */
     81 const struct floatformat floatformat_ieee_single_big =
     82 {
     83   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
     84   floatformat_intbit_no,
     85   "floatformat_ieee_single_big",
     86   floatformat_always_valid,
     87   NULL
     88 };
     89 const struct floatformat floatformat_ieee_single_little =
     90 {
     91   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
     92   floatformat_intbit_no,
     93   "floatformat_ieee_single_little",
     94   floatformat_always_valid,
     95   NULL
     96 };
     97 const struct floatformat floatformat_ieee_double_big =
     98 {
     99   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
    100   floatformat_intbit_no,
    101   "floatformat_ieee_double_big",
    102   floatformat_always_valid,
    103   NULL
    104 };
    105 const struct floatformat floatformat_ieee_double_little =
    106 {
    107   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
    108   floatformat_intbit_no,
    109   "floatformat_ieee_double_little",
    110   floatformat_always_valid,
    111   NULL
    112 };
    113 
    114 /* floatformat for IEEE double, little endian byte order, with big endian word
    115    ordering, as on the ARM.  */
    116 
    117 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
    118 {
    119   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
    120   floatformat_intbit_no,
    121   "floatformat_ieee_double_littlebyte_bigword",
    122   floatformat_always_valid,
    123   NULL
    124 };
    125 
    126 /* floatformat for VAX.  Not quite IEEE, but close enough.  */
    127 
    128 const struct floatformat floatformat_vax_f =
    129 {
    130   floatformat_vax, 32, 0, 1, 8, 129, 0, 9, 23,
    131   floatformat_intbit_no,
    132   "floatformat_vax_f",
    133   floatformat_always_valid,
    134   NULL
    135 };
    136 const struct floatformat floatformat_vax_d =
    137 {
    138   floatformat_vax, 64, 0, 1, 8, 129, 0, 9, 55,
    139   floatformat_intbit_no,
    140   "floatformat_vax_d",
    141   floatformat_always_valid,
    142   NULL
    143 };
    144 const struct floatformat floatformat_vax_g =
    145 {
    146   floatformat_vax, 64, 0, 1, 11, 1025, 0, 12, 52,
    147   floatformat_intbit_no,
    148   "floatformat_vax_g",
    149   floatformat_always_valid,
    150   NULL
    151 };
    152 
    153 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt,
    154 					  const void *from);
    155 
    156 static int
    157 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const void *from)
    158 {
    159   /* In the i387 double-extended format, if the exponent is all ones,
    160      then the integer bit must be set.  If the exponent is neither 0
    161      nor ~0, the intbit must also be set.  Only if the exponent is
    162      zero can it be zero, and then it must be zero.  */
    163   unsigned long exponent, int_bit;
    164   const unsigned char *ufrom = (const unsigned char *) from;
    165 
    166   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    167 			fmt->exp_start, fmt->exp_len);
    168   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    169 		       fmt->man_start, 1);
    170 
    171   if ((exponent == 0) != (int_bit == 0))
    172     return 0;
    173   else
    174     return 1;
    175 }
    176 
    177 const struct floatformat floatformat_i387_ext =
    178 {
    179   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
    180   floatformat_intbit_yes,
    181   "floatformat_i387_ext",
    182   floatformat_i387_ext_is_valid,
    183   NULL
    184 };
    185 const struct floatformat floatformat_m68881_ext =
    186 {
    187   /* Note that the bits from 16 to 31 are unused.  */
    188   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
    189   floatformat_intbit_yes,
    190   "floatformat_m68881_ext",
    191   floatformat_always_valid,
    192   NULL
    193 };
    194 const struct floatformat floatformat_i960_ext =
    195 {
    196   /* Note that the bits from 0 to 15 are unused.  */
    197   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
    198   floatformat_intbit_yes,
    199   "floatformat_i960_ext",
    200   floatformat_always_valid,
    201   NULL
    202 };
    203 const struct floatformat floatformat_m88110_ext =
    204 {
    205   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
    206   floatformat_intbit_yes,
    207   "floatformat_m88110_ext",
    208   floatformat_always_valid,
    209   NULL
    210 };
    211 const struct floatformat floatformat_m88110_harris_ext =
    212 {
    213   /* Harris uses raw format 128 bytes long, but the number is just an ieee
    214      double, and the last 64 bits are wasted. */
    215   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
    216   floatformat_intbit_no,
    217   "floatformat_m88110_ext_harris",
    218   floatformat_always_valid,
    219   NULL
    220 };
    221 const struct floatformat floatformat_arm_ext_big =
    222 {
    223   /* Bits 1 to 16 are unused.  */
    224   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
    225   floatformat_intbit_yes,
    226   "floatformat_arm_ext_big",
    227   floatformat_always_valid,
    228   NULL
    229 };
    230 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
    231 {
    232   /* Bits 1 to 16 are unused.  */
    233   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
    234   floatformat_intbit_yes,
    235   "floatformat_arm_ext_littlebyte_bigword",
    236   floatformat_always_valid,
    237   NULL
    238 };
    239 const struct floatformat floatformat_ia64_spill_big =
    240 {
    241   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
    242   floatformat_intbit_yes,
    243   "floatformat_ia64_spill_big",
    244   floatformat_always_valid,
    245   NULL
    246 };
    247 const struct floatformat floatformat_ia64_spill_little =
    248 {
    249   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
    250   floatformat_intbit_yes,
    251   "floatformat_ia64_spill_little",
    252   floatformat_always_valid,
    253   NULL
    254 };
    255 const struct floatformat floatformat_ia64_quad_big =
    256 {
    257   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
    258   floatformat_intbit_no,
    259   "floatformat_ia64_quad_big",
    260   floatformat_always_valid,
    261   NULL
    262 };
    263 const struct floatformat floatformat_ia64_quad_little =
    264 {
    265   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
    266   floatformat_intbit_no,
    267   "floatformat_ia64_quad_little",
    268   floatformat_always_valid,
    269   NULL
    270 };
    271 
    272 static int
    273 floatformat_ibm_long_double_is_valid (const struct floatformat *fmt,
    274 				      const void *from)
    275 {
    276   const unsigned char *ufrom = (const unsigned char *) from;
    277   const struct floatformat *hfmt = fmt->split_half;
    278   long top_exp, bot_exp;
    279   int top_nan = 0;
    280 
    281   top_exp = get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    282 		       hfmt->exp_start, hfmt->exp_len);
    283   bot_exp = get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
    284 		       hfmt->exp_start, hfmt->exp_len);
    285 
    286   if ((unsigned long) top_exp == hfmt->exp_nan)
    287     top_nan = mant_bits_set (hfmt, ufrom);
    288 
    289   /* A NaN is valid with any low part.  */
    290   if (top_nan)
    291     return 1;
    292 
    293   /* An infinity, zero or denormal requires low part 0 (positive or
    294      negative).  */
    295   if ((unsigned long) top_exp == hfmt->exp_nan || top_exp == 0)
    296     {
    297       if (bot_exp != 0)
    298 	return 0;
    299 
    300       return !mant_bits_set (hfmt, ufrom + 8);
    301     }
    302 
    303   /* The top part is now a finite normal value.  The long double value
    304      is the sum of the two parts, and the top part must equal the
    305      result of rounding the long double value to nearest double.  Thus
    306      the bottom part must be <= 0.5ulp of the top part in absolute
    307      value, and if it is < 0.5ulp then the long double is definitely
    308      valid.  */
    309   if (bot_exp < top_exp - 53)
    310     return 1;
    311   if (bot_exp > top_exp - 53 && bot_exp != 0)
    312     return 0;
    313   if (bot_exp == 0)
    314     {
    315       /* The bottom part is 0 or denormal.  Determine which, and if
    316 	 denormal the first two set bits.  */
    317       int first_bit = -1, second_bit = -1, cur_bit;
    318       for (cur_bit = 0; (unsigned int) cur_bit < hfmt->man_len; cur_bit++)
    319 	if (get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
    320 		       hfmt->man_start + cur_bit, 1))
    321 	  {
    322 	    if (first_bit == -1)
    323 	      first_bit = cur_bit;
    324 	    else
    325 	      {
    326 		second_bit = cur_bit;
    327 		break;
    328 	      }
    329 	  }
    330       /* Bottom part 0 is OK.  */
    331       if (first_bit == -1)
    332 	return 1;
    333       /* The real exponent of the bottom part is -first_bit.  */
    334       if (-first_bit < top_exp - 53)
    335 	return 1;
    336       if (-first_bit > top_exp - 53)
    337 	return 0;
    338       /* The bottom part is at least 0.5ulp of the top part.  For this
    339 	 to be OK, the bottom part must be exactly 0.5ulp (i.e. no
    340 	 more bits set) and the top part must have last bit 0.  */
    341       if (second_bit != -1)
    342 	return 0;
    343       return !get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    344 			 hfmt->man_start + hfmt->man_len - 1, 1);
    345     }
    346   else
    347     {
    348       /* The bottom part is at least 0.5ulp of the top part.  For this
    349 	 to be OK, it must be exactly 0.5ulp (i.e. no explicit bits
    350 	 set) and the top part must have last bit 0.  */
    351       if (get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    352 		     hfmt->man_start + hfmt->man_len - 1, 1))
    353 	return 0;
    354       return !mant_bits_set (hfmt, ufrom + 8);
    355     }
    356 }
    357 
    358 const struct floatformat floatformat_ibm_long_double =
    359 {
    360   floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52,
    361   floatformat_intbit_no,
    362   "floatformat_ibm_long_double",
    363   floatformat_ibm_long_double_is_valid,
    364   &floatformat_ieee_double_big
    365 };
    366 
    367 
    369 #ifndef min
    370 #define min(a, b) ((a) < (b) ? (a) : (b))
    371 #endif
    372 
    373 /* Return 1 if any bits are explicitly set in the mantissa of UFROM,
    374    format FMT, 0 otherwise.  */
    375 static int
    376 mant_bits_set (const struct floatformat *fmt, const unsigned char *ufrom)
    377 {
    378   unsigned int mant_bits, mant_off;
    379   int mant_bits_left;
    380 
    381   mant_off = fmt->man_start;
    382   mant_bits_left = fmt->man_len;
    383   while (mant_bits_left > 0)
    384     {
    385       mant_bits = min (mant_bits_left, 32);
    386 
    387       if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
    388 		     mant_off, mant_bits) != 0)
    389 	return 1;
    390 
    391       mant_off += mant_bits;
    392       mant_bits_left -= mant_bits;
    393     }
    394   return 0;
    395 }
    396 
    397 /* Extract a field which starts at START and is LEN bits long.  DATA and
    398    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
    399 static unsigned long
    400 get_field (const unsigned char *data, enum floatformat_byteorders order,
    401            unsigned int total_len, unsigned int start, unsigned int len)
    402 {
    403   unsigned long result = 0;
    404   unsigned int cur_byte;
    405   int lo_bit, hi_bit, cur_bitshift = 0;
    406   int nextbyte = (order == floatformat_little) ? 1 : -1;
    407 
    408   /* Start is in big-endian bit order!  Fix that first.  */
    409   start = total_len - (start + len);
    410 
    411   /* Start at the least significant part of the field.  */
    412   if (order == floatformat_little)
    413     cur_byte = start / FLOATFORMAT_CHAR_BIT;
    414   else
    415     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
    416 
    417   lo_bit = start % FLOATFORMAT_CHAR_BIT;
    418   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
    419 
    420   do
    421     {
    422       unsigned int shifted = *(data + cur_byte) >> lo_bit;
    423       unsigned int bits = hi_bit - lo_bit;
    424       unsigned int mask = (1 << bits) - 1;
    425       result |= (shifted & mask) << cur_bitshift;
    426       len -= bits;
    427       cur_bitshift += bits;
    428       cur_byte += nextbyte;
    429       lo_bit = 0;
    430       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
    431     }
    432   while (len != 0);
    433 
    434   return result;
    435 }
    436 
    437 /* Convert from FMT to a double.
    438    FROM is the address of the extended float.
    439    Store the double in *TO.  */
    440 
    441 void
    442 floatformat_to_double (const struct floatformat *fmt,
    443                        const void *from, double *to)
    444 {
    445   const unsigned char *ufrom = (const unsigned char *) from;
    446   double dto;
    447   long exponent;
    448   unsigned long mant;
    449   unsigned int mant_bits, mant_off;
    450   int mant_bits_left;
    451   int special_exponent;		/* It's a NaN, denorm or zero */
    452 
    453   /* Split values are not handled specially, since the top half has
    454      the correctly rounded double value (in the only supported case of
    455      split values).  */
    456 
    457   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    458 			fmt->exp_start, fmt->exp_len);
    459 
    460   /* If the exponent indicates a NaN, we don't have information to
    461      decide what to do.  So we handle it like IEEE, except that we
    462      don't try to preserve the type of NaN.  FIXME.  */
    463   if ((unsigned long) exponent == fmt->exp_nan)
    464     {
    465       int nan = mant_bits_set (fmt, ufrom);
    466 
    467       /* On certain systems (such as GNU/Linux), the use of the
    468 	 INFINITY macro below may generate a warning that can not be
    469 	 silenced due to a bug in GCC (PR preprocessor/11931).  The
    470 	 preprocessor fails to recognise the __extension__ keyword in
    471 	 conjunction with the GNU/C99 extension for hexadecimal
    472 	 floating point constants and will issue a warning when
    473 	 compiling with -pedantic.  */
    474       if (nan)
    475 	dto = NAN;
    476       else
    477 #ifdef __vax__
    478 	dto = HUGE_VAL;
    479 #else
    480 	dto = INFINITY;
    481 #endif
    482 
    483       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
    484 	dto = -dto;
    485 
    486       *to = dto;
    487 
    488       return;
    489     }
    490 
    491   mant_bits_left = fmt->man_len;
    492   mant_off = fmt->man_start;
    493   dto = 0.0;
    494 
    495   special_exponent = exponent == 0 || (unsigned long) exponent == fmt->exp_nan;
    496 
    497   /* Don't bias zero's, denorms or NaNs.  */
    498   if (!special_exponent)
    499     exponent -= fmt->exp_bias;
    500 
    501   /* Build the result algebraically.  Might go infinite, underflow, etc;
    502      who cares. */
    503 
    504   /* If this format uses a hidden bit, explicitly add it in now.  Otherwise,
    505      increment the exponent by one to account for the integer bit.  */
    506 
    507   if (!special_exponent)
    508     {
    509       if (fmt->intbit == floatformat_intbit_no)
    510 	dto = ldexp (1.0, exponent);
    511       else
    512 	exponent++;
    513     }
    514 
    515   while (mant_bits_left > 0)
    516     {
    517       mant_bits = min (mant_bits_left, 32);
    518 
    519       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    520 			 mant_off, mant_bits);
    521 
    522       /* Handle denormalized numbers.  FIXME: What should we do for
    523 	 non-IEEE formats?  */
    524       if (special_exponent && exponent == 0 && mant != 0)
    525 	dto += ldexp ((double)mant,
    526 		      (- fmt->exp_bias
    527 		       - mant_bits
    528 		       - (mant_off - fmt->man_start)
    529 		       + 1));
    530       else
    531 	dto += ldexp ((double)mant, exponent - mant_bits);
    532       if (exponent != 0)
    533 	exponent -= mant_bits;
    534       mant_off += mant_bits;
    535       mant_bits_left -= mant_bits;
    536     }
    537 
    538   /* Negate it if negative.  */
    539   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
    540     dto = -dto;
    541   *to = dto;
    542 }
    543 
    544 static void put_field (unsigned char *, enum floatformat_byteorders,
    546                        unsigned int,
    547                        unsigned int,
    548                        unsigned int,
    549                        unsigned long);
    550 
    551 /* Set a field which starts at START and is LEN bits long.  DATA and
    552    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
    553 static void
    554 put_field (unsigned char *data, enum floatformat_byteorders order,
    555            unsigned int total_len, unsigned int start, unsigned int len,
    556            unsigned long stuff_to_put)
    557 {
    558   unsigned int cur_byte;
    559   int lo_bit, hi_bit;
    560   int nextbyte = (order == floatformat_little) ? 1 : -1;
    561 
    562   /* Start is in big-endian bit order!  Fix that first.  */
    563   start = total_len - (start + len);
    564 
    565   /* Start at the least significant part of the field.  */
    566   if (order == floatformat_little)
    567     cur_byte = start / FLOATFORMAT_CHAR_BIT;
    568   else
    569     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
    570 
    571   lo_bit = start % FLOATFORMAT_CHAR_BIT;
    572   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
    573 
    574   do
    575     {
    576       unsigned char *byte_ptr = data + cur_byte;
    577       unsigned int bits = hi_bit - lo_bit;
    578       unsigned int mask = ((1 << bits) - 1) << lo_bit;
    579       *byte_ptr = (*byte_ptr & ~mask) | ((stuff_to_put << lo_bit) & mask);
    580       stuff_to_put >>= bits;
    581       len -= bits;
    582       cur_byte += nextbyte;
    583       lo_bit = 0;
    584       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
    585     }
    586   while (len != 0);
    587 }
    588 
    589 /* The converse: convert the double *FROM to an extended float
    590    and store where TO points.  Neither FROM nor TO have any alignment
    591    restrictions.  */
    592 
    593 void
    594 floatformat_from_double (const struct floatformat *fmt,
    595                          const double *from, void *to)
    596 {
    597   double dfrom;
    598   int exponent;
    599   double mant;
    600   unsigned int mant_bits, mant_off;
    601   int mant_bits_left;
    602   unsigned char *uto = (unsigned char *) to;
    603 
    604   dfrom = *from;
    605   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
    606 
    607   /* Split values are not handled specially, since a bottom half of
    608      zero is correct for any value representable as double (in the
    609      only supported case of split values).  */
    610 
    611   /* If negative, set the sign bit.  */
    612   if (dfrom < 0)
    613     {
    614       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
    615       dfrom = -dfrom;
    616     }
    617 
    618   if (dfrom == 0)
    619     {
    620       /* 0.0.  */
    621       return;
    622     }
    623 
    624   if (dfrom != dfrom)
    625     {
    626       /* NaN.  */
    627       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    628 		 fmt->exp_len, fmt->exp_nan);
    629       /* Be sure it's not infinity, but NaN value is irrelevant.  */
    630       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
    631 		 32, 1);
    632       return;
    633     }
    634 
    635   if (dfrom + dfrom == dfrom)
    636     {
    637       /* This can only happen for an infinite value (or zero, which we
    638 	 already handled above).  */
    639       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    640 		 fmt->exp_len, fmt->exp_nan);
    641       return;
    642     }
    643 
    644   mant = frexp (dfrom, &exponent);
    645   if (exponent + fmt->exp_bias - 1 > 0)
    646     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    647 	       fmt->exp_len, exponent + fmt->exp_bias - 1);
    648   else
    649     {
    650       /* Handle a denormalized number.  FIXME: What should we do for
    651 	 non-IEEE formats?  */
    652       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    653 		 fmt->exp_len, 0);
    654       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
    655     }
    656 
    657   mant_bits_left = fmt->man_len;
    658   mant_off = fmt->man_start;
    659   while (mant_bits_left > 0)
    660     {
    661       unsigned long mant_long;
    662       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
    663 
    664       mant *= 4294967296.0;
    665       mant_long = (unsigned long)mant;
    666       mant -= mant_long;
    667 
    668       /* If the integer bit is implicit, and we are not creating a
    669 	 denormalized number, then we need to discard it.  */
    670       if ((unsigned int) mant_bits_left == fmt->man_len
    671 	  && fmt->intbit == floatformat_intbit_no
    672 	  && exponent + fmt->exp_bias - 1 > 0)
    673 	{
    674 	  mant_long &= 0x7fffffff;
    675 	  mant_bits -= 1;
    676 	}
    677       else if (mant_bits < 32)
    678 	{
    679 	  /* The bits we want are in the most significant MANT_BITS bits of
    680 	     mant_long.  Move them to the least significant.  */
    681 	  mant_long >>= 32 - mant_bits;
    682 	}
    683 
    684       put_field (uto, fmt->byteorder, fmt->totalsize,
    685 		 mant_off, mant_bits, mant_long);
    686       mant_off += mant_bits;
    687       mant_bits_left -= mant_bits;
    688     }
    689 }
    690 
    691 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
    692 
    693 int
    694 floatformat_is_valid (const struct floatformat *fmt, const void *from)
    695 {
    696   return fmt->is_valid (fmt, from);
    697 }
    698 
    699 
    700 #ifdef IEEE_DEBUG
    701 
    702 #include <stdio.h>
    703 
    704 /* This is to be run on a host which uses IEEE floating point.  */
    705 
    706 void
    707 ieee_test (double n)
    708 {
    709   double result;
    710 
    711   floatformat_to_double (&floatformat_ieee_double_little, &n, &result);
    712   if ((n != result && (! isnan (n) || ! isnan (result)))
    713       || (n < 0 && result >= 0)
    714       || (n >= 0 && result < 0))
    715     printf ("Differ(to): %.20g -> %.20g\n", n, result);
    716 
    717   floatformat_from_double (&floatformat_ieee_double_little, &n, &result);
    718   if ((n != result && (! isnan (n) || ! isnan (result)))
    719       || (n < 0 && result >= 0)
    720       || (n >= 0 && result < 0))
    721     printf ("Differ(from): %.20g -> %.20g\n", n, result);
    722 
    723 #if 0
    724   {
    725     char exten[16];
    726 
    727     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
    728     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
    729     if (n != result)
    730       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
    731   }
    732 #endif
    733 
    734 #if IEEE_DEBUG > 1
    735   /* This is to be run on a host which uses 68881 format.  */
    736   {
    737     long double ex = *(long double *)exten;
    738     if (ex != n)
    739       printf ("Differ(from vs. extended): %.20g\n", n);
    740   }
    741 #endif
    742 }
    743 
    744 int
    745 main (void)
    746 {
    747   ieee_test (0.0);
    748   ieee_test (0.5);
    749   ieee_test (256.0);
    750   ieee_test (0.12345);
    751   ieee_test (234235.78907234);
    752   ieee_test (-512.0);
    753   ieee_test (-0.004321);
    754   ieee_test (1.2E-70);
    755   ieee_test (1.2E-316);
    756   ieee_test (4.9406564584124654E-324);
    757   ieee_test (- 4.9406564584124654E-324);
    758   ieee_test (- 0.0);
    759   ieee_test (- INFINITY);
    760   ieee_test (- NAN);
    761   ieee_test (INFINITY);
    762   ieee_test (NAN);
    763   return 0;
    764 }
    765 #endif
    766