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floatformat.c revision 1.1.1.2
      1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
      2    Copyright 1991, 1994, 1999, 2000, 2003, 2005, 2006, 2010, 2012
      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 half, single and double, big and little endian.  */
     81 const struct floatformat floatformat_ieee_half_big =
     82 {
     83   floatformat_big, 16, 0, 1, 5, 15, 31, 6, 10,
     84   floatformat_intbit_no,
     85   "floatformat_ieee_half_big",
     86   floatformat_always_valid,
     87   NULL
     88 };
     89 const struct floatformat floatformat_ieee_half_little =
     90 {
     91   floatformat_little, 16, 0, 1, 5, 15, 31, 6, 10,
     92   floatformat_intbit_no,
     93   "floatformat_ieee_half_little",
     94   floatformat_always_valid,
     95   NULL
     96 };
     97 const struct floatformat floatformat_ieee_single_big =
     98 {
     99   floatformat_big, 32, 0, 1, 8, 127, 255, 9, 23,
    100   floatformat_intbit_no,
    101   "floatformat_ieee_single_big",
    102   floatformat_always_valid,
    103   NULL
    104 };
    105 const struct floatformat floatformat_ieee_single_little =
    106 {
    107   floatformat_little, 32, 0, 1, 8, 127, 255, 9, 23,
    108   floatformat_intbit_no,
    109   "floatformat_ieee_single_little",
    110   floatformat_always_valid,
    111   NULL
    112 };
    113 const struct floatformat floatformat_ieee_double_big =
    114 {
    115   floatformat_big, 64, 0, 1, 11, 1023, 2047, 12, 52,
    116   floatformat_intbit_no,
    117   "floatformat_ieee_double_big",
    118   floatformat_always_valid,
    119   NULL
    120 };
    121 const struct floatformat floatformat_ieee_double_little =
    122 {
    123   floatformat_little, 64, 0, 1, 11, 1023, 2047, 12, 52,
    124   floatformat_intbit_no,
    125   "floatformat_ieee_double_little",
    126   floatformat_always_valid,
    127   NULL
    128 };
    129 
    130 /* floatformat for IEEE double, little endian byte order, with big endian word
    131    ordering, as on the ARM.  */
    132 
    133 const struct floatformat floatformat_ieee_double_littlebyte_bigword =
    134 {
    135   floatformat_littlebyte_bigword, 64, 0, 1, 11, 1023, 2047, 12, 52,
    136   floatformat_intbit_no,
    137   "floatformat_ieee_double_littlebyte_bigword",
    138   floatformat_always_valid,
    139   NULL
    140 };
    141 
    142 /* floatformat for VAX.  Not quite IEEE, but close enough.  */
    143 
    144 const struct floatformat floatformat_vax_f =
    145 {
    146   floatformat_vax, 32, 0, 1, 8, 129, 0, 9, 23,
    147   floatformat_intbit_no,
    148   "floatformat_vax_f",
    149   floatformat_always_valid,
    150   NULL
    151 };
    152 const struct floatformat floatformat_vax_d =
    153 {
    154   floatformat_vax, 64, 0, 1, 8, 129, 0, 9, 55,
    155   floatformat_intbit_no,
    156   "floatformat_vax_d",
    157   floatformat_always_valid,
    158   NULL
    159 };
    160 const struct floatformat floatformat_vax_g =
    161 {
    162   floatformat_vax, 64, 0, 1, 11, 1025, 0, 12, 52,
    163   floatformat_intbit_no,
    164   "floatformat_vax_g",
    165   floatformat_always_valid,
    166   NULL
    167 };
    168 
    169 static int floatformat_i387_ext_is_valid (const struct floatformat *fmt,
    170 					  const void *from);
    171 
    172 static int
    173 floatformat_i387_ext_is_valid (const struct floatformat *fmt, const void *from)
    174 {
    175   /* In the i387 double-extended format, if the exponent is all ones,
    176      then the integer bit must be set.  If the exponent is neither 0
    177      nor ~0, the intbit must also be set.  Only if the exponent is
    178      zero can it be zero, and then it must be zero.  */
    179   unsigned long exponent, int_bit;
    180   const unsigned char *ufrom = (const unsigned char *) from;
    181 
    182   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    183 			fmt->exp_start, fmt->exp_len);
    184   int_bit = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    185 		       fmt->man_start, 1);
    186 
    187   if ((exponent == 0) != (int_bit == 0))
    188     return 0;
    189   else
    190     return 1;
    191 }
    192 
    193 const struct floatformat floatformat_i387_ext =
    194 {
    195   floatformat_little, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
    196   floatformat_intbit_yes,
    197   "floatformat_i387_ext",
    198   floatformat_i387_ext_is_valid,
    199   NULL
    200 };
    201 const struct floatformat floatformat_m68881_ext =
    202 {
    203   /* Note that the bits from 16 to 31 are unused.  */
    204   floatformat_big, 96, 0, 1, 15, 0x3fff, 0x7fff, 32, 64,
    205   floatformat_intbit_yes,
    206   "floatformat_m68881_ext",
    207   floatformat_always_valid,
    208   NULL
    209 };
    210 const struct floatformat floatformat_i960_ext =
    211 {
    212   /* Note that the bits from 0 to 15 are unused.  */
    213   floatformat_little, 96, 16, 17, 15, 0x3fff, 0x7fff, 32, 64,
    214   floatformat_intbit_yes,
    215   "floatformat_i960_ext",
    216   floatformat_always_valid,
    217   NULL
    218 };
    219 const struct floatformat floatformat_m88110_ext =
    220 {
    221   floatformat_big, 80, 0, 1, 15, 0x3fff, 0x7fff, 16, 64,
    222   floatformat_intbit_yes,
    223   "floatformat_m88110_ext",
    224   floatformat_always_valid,
    225   NULL
    226 };
    227 const struct floatformat floatformat_m88110_harris_ext =
    228 {
    229   /* Harris uses raw format 128 bytes long, but the number is just an ieee
    230      double, and the last 64 bits are wasted. */
    231   floatformat_big,128, 0, 1, 11,  0x3ff,  0x7ff, 12, 52,
    232   floatformat_intbit_no,
    233   "floatformat_m88110_ext_harris",
    234   floatformat_always_valid,
    235   NULL
    236 };
    237 const struct floatformat floatformat_arm_ext_big =
    238 {
    239   /* Bits 1 to 16 are unused.  */
    240   floatformat_big, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
    241   floatformat_intbit_yes,
    242   "floatformat_arm_ext_big",
    243   floatformat_always_valid,
    244   NULL
    245 };
    246 const struct floatformat floatformat_arm_ext_littlebyte_bigword =
    247 {
    248   /* Bits 1 to 16 are unused.  */
    249   floatformat_littlebyte_bigword, 96, 0, 17, 15, 0x3fff, 0x7fff, 32, 64,
    250   floatformat_intbit_yes,
    251   "floatformat_arm_ext_littlebyte_bigword",
    252   floatformat_always_valid,
    253   NULL
    254 };
    255 const struct floatformat floatformat_ia64_spill_big =
    256 {
    257   floatformat_big, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
    258   floatformat_intbit_yes,
    259   "floatformat_ia64_spill_big",
    260   floatformat_always_valid,
    261   NULL
    262 };
    263 const struct floatformat floatformat_ia64_spill_little =
    264 {
    265   floatformat_little, 128, 0, 1, 17, 65535, 0x1ffff, 18, 64,
    266   floatformat_intbit_yes,
    267   "floatformat_ia64_spill_little",
    268   floatformat_always_valid,
    269   NULL
    270 };
    271 const struct floatformat floatformat_ia64_quad_big =
    272 {
    273   floatformat_big, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
    274   floatformat_intbit_no,
    275   "floatformat_ia64_quad_big",
    276   floatformat_always_valid,
    277   NULL
    278 };
    279 const struct floatformat floatformat_ia64_quad_little =
    280 {
    281   floatformat_little, 128, 0, 1, 15, 16383, 0x7fff, 16, 112,
    282   floatformat_intbit_no,
    283   "floatformat_ia64_quad_little",
    284   floatformat_always_valid,
    285   NULL
    286 };
    287 
    288 static int
    289 floatformat_ibm_long_double_is_valid (const struct floatformat *fmt,
    290 				      const void *from)
    291 {
    292   const unsigned char *ufrom = (const unsigned char *) from;
    293   const struct floatformat *hfmt = fmt->split_half;
    294   long top_exp, bot_exp;
    295   int top_nan = 0;
    296 
    297   top_exp = get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    298 		       hfmt->exp_start, hfmt->exp_len);
    299   bot_exp = get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
    300 		       hfmt->exp_start, hfmt->exp_len);
    301 
    302   if ((unsigned long) top_exp == hfmt->exp_nan)
    303     top_nan = mant_bits_set (hfmt, ufrom);
    304 
    305   /* A NaN is valid with any low part.  */
    306   if (top_nan)
    307     return 1;
    308 
    309   /* An infinity, zero or denormal requires low part 0 (positive or
    310      negative).  */
    311   if ((unsigned long) top_exp == hfmt->exp_nan || top_exp == 0)
    312     {
    313       if (bot_exp != 0)
    314 	return 0;
    315 
    316       return !mant_bits_set (hfmt, ufrom + 8);
    317     }
    318 
    319   /* The top part is now a finite normal value.  The long double value
    320      is the sum of the two parts, and the top part must equal the
    321      result of rounding the long double value to nearest double.  Thus
    322      the bottom part must be <= 0.5ulp of the top part in absolute
    323      value, and if it is < 0.5ulp then the long double is definitely
    324      valid.  */
    325   if (bot_exp < top_exp - 53)
    326     return 1;
    327   if (bot_exp > top_exp - 53 && bot_exp != 0)
    328     return 0;
    329   if (bot_exp == 0)
    330     {
    331       /* The bottom part is 0 or denormal.  Determine which, and if
    332 	 denormal the first two set bits.  */
    333       int first_bit = -1, second_bit = -1, cur_bit;
    334       for (cur_bit = 0; (unsigned int) cur_bit < hfmt->man_len; cur_bit++)
    335 	if (get_field (ufrom + 8, hfmt->byteorder, hfmt->totalsize,
    336 		       hfmt->man_start + cur_bit, 1))
    337 	  {
    338 	    if (first_bit == -1)
    339 	      first_bit = cur_bit;
    340 	    else
    341 	      {
    342 		second_bit = cur_bit;
    343 		break;
    344 	      }
    345 	  }
    346       /* Bottom part 0 is OK.  */
    347       if (first_bit == -1)
    348 	return 1;
    349       /* The real exponent of the bottom part is -first_bit.  */
    350       if (-first_bit < top_exp - 53)
    351 	return 1;
    352       if (-first_bit > top_exp - 53)
    353 	return 0;
    354       /* The bottom part is at least 0.5ulp of the top part.  For this
    355 	 to be OK, the bottom part must be exactly 0.5ulp (i.e. no
    356 	 more bits set) and the top part must have last bit 0.  */
    357       if (second_bit != -1)
    358 	return 0;
    359       return !get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    360 			 hfmt->man_start + hfmt->man_len - 1, 1);
    361     }
    362   else
    363     {
    364       /* The bottom part is at least 0.5ulp of the top part.  For this
    365 	 to be OK, it must be exactly 0.5ulp (i.e. no explicit bits
    366 	 set) and the top part must have last bit 0.  */
    367       if (get_field (ufrom, hfmt->byteorder, hfmt->totalsize,
    368 		     hfmt->man_start + hfmt->man_len - 1, 1))
    369 	return 0;
    370       return !mant_bits_set (hfmt, ufrom + 8);
    371     }
    372 }
    373 
    374 const struct floatformat floatformat_ibm_long_double =
    375 {
    376   floatformat_big, 128, 0, 1, 11, 1023, 2047, 12, 52,
    377   floatformat_intbit_no,
    378   "floatformat_ibm_long_double",
    379   floatformat_ibm_long_double_is_valid,
    380   &floatformat_ieee_double_big
    381 };
    382 
    383 
    385 #ifndef min
    386 #define min(a, b) ((a) < (b) ? (a) : (b))
    387 #endif
    388 
    389 /* Return 1 if any bits are explicitly set in the mantissa of UFROM,
    390    format FMT, 0 otherwise.  */
    391 static int
    392 mant_bits_set (const struct floatformat *fmt, const unsigned char *ufrom)
    393 {
    394   unsigned int mant_bits, mant_off;
    395   int mant_bits_left;
    396 
    397   mant_off = fmt->man_start;
    398   mant_bits_left = fmt->man_len;
    399   while (mant_bits_left > 0)
    400     {
    401       mant_bits = min (mant_bits_left, 32);
    402 
    403       if (get_field (ufrom, fmt->byteorder, fmt->totalsize,
    404 		     mant_off, mant_bits) != 0)
    405 	return 1;
    406 
    407       mant_off += mant_bits;
    408       mant_bits_left -= mant_bits;
    409     }
    410   return 0;
    411 }
    412 
    413 /* Extract a field which starts at START and is LEN bits long.  DATA and
    414    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
    415 static unsigned long
    416 get_field (const unsigned char *data, enum floatformat_byteorders order,
    417            unsigned int total_len, unsigned int start, unsigned int len)
    418 {
    419   unsigned long result = 0;
    420   unsigned int cur_byte;
    421   int lo_bit, hi_bit, cur_bitshift = 0;
    422   int nextbyte = (order == floatformat_little) ? 1 : -1;
    423 
    424   /* Start is in big-endian bit order!  Fix that first.  */
    425   start = total_len - (start + len);
    426 
    427   /* Start at the least significant part of the field.  */
    428   if (order == floatformat_little)
    429     cur_byte = start / FLOATFORMAT_CHAR_BIT;
    430   else
    431     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
    432 
    433   lo_bit = start % FLOATFORMAT_CHAR_BIT;
    434   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
    435 
    436   do
    437     {
    438       unsigned int shifted = *(data + cur_byte) >> lo_bit;
    439       unsigned int bits = hi_bit - lo_bit;
    440       unsigned int mask = (1 << bits) - 1;
    441       result |= (shifted & mask) << cur_bitshift;
    442       len -= bits;
    443       cur_bitshift += bits;
    444       cur_byte += nextbyte;
    445       lo_bit = 0;
    446       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
    447     }
    448   while (len != 0);
    449 
    450   return result;
    451 }
    452 
    453 /* Convert from FMT to a double.
    454    FROM is the address of the extended float.
    455    Store the double in *TO.  */
    456 
    457 void
    458 floatformat_to_double (const struct floatformat *fmt,
    459                        const void *from, double *to)
    460 {
    461   const unsigned char *ufrom = (const unsigned char *) from;
    462   double dto;
    463   long exponent;
    464   unsigned long mant;
    465   unsigned int mant_bits, mant_off;
    466   int mant_bits_left;
    467 
    468   /* Split values are not handled specially, since the top half has
    469      the correctly rounded double value (in the only supported case of
    470      split values).  */
    471 
    472   exponent = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    473 			fmt->exp_start, fmt->exp_len);
    474 
    475   /* If the exponent indicates a NaN, we don't have information to
    476      decide what to do.  So we handle it like IEEE, except that we
    477      don't try to preserve the type of NaN.  FIXME.  */
    478   if ((unsigned long) exponent == fmt->exp_nan)
    479     {
    480       int nan = mant_bits_set (fmt, ufrom);
    481 
    482       /* On certain systems (such as GNU/Linux), the use of the
    483 	 INFINITY macro below may generate a warning that can not be
    484 	 silenced due to a bug in GCC (PR preprocessor/11931).  The
    485 	 preprocessor fails to recognise the __extension__ keyword in
    486 	 conjunction with the GNU/C99 extension for hexadecimal
    487 	 floating point constants and will issue a warning when
    488 	 compiling with -pedantic.  */
    489       if (nan)
    490 	dto = NAN;
    491       else
    492 	dto = INFINITY;
    493 
    494       if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
    495 	dto = -dto;
    496 
    497       *to = dto;
    498 
    499       return;
    500     }
    501 
    502   mant_bits_left = fmt->man_len;
    503   mant_off = fmt->man_start;
    504   dto = 0.0;
    505 
    506   /* Build the result algebraically.  Might go infinite, underflow, etc;
    507      who cares. */
    508 
    509   /* For denorms use minimum exponent.  */
    510   if (exponent == 0)
    511     exponent = 1 - fmt->exp_bias;
    512   else
    513     {
    514       exponent -= fmt->exp_bias;
    515 
    516       /* If this format uses a hidden bit, explicitly add it in now.
    517 	 Otherwise, increment the exponent by one to account for the
    518 	 integer bit.  */
    519 
    520       if (fmt->intbit == floatformat_intbit_no)
    521 	dto = ldexp (1.0, exponent);
    522       else
    523 	exponent++;
    524     }
    525 
    526   while (mant_bits_left > 0)
    527     {
    528       mant_bits = min (mant_bits_left, 32);
    529 
    530       mant = get_field (ufrom, fmt->byteorder, fmt->totalsize,
    531 			 mant_off, mant_bits);
    532 
    533       dto += ldexp ((double) mant, exponent - mant_bits);
    534       exponent -= mant_bits;
    535       mant_off += mant_bits;
    536       mant_bits_left -= mant_bits;
    537     }
    538 
    539   /* Negate it if negative.  */
    540   if (get_field (ufrom, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1))
    541     dto = -dto;
    542   *to = dto;
    543 }
    544 
    545 static void put_field (unsigned char *, enum floatformat_byteorders,
    547                        unsigned int,
    548                        unsigned int,
    549                        unsigned int,
    550                        unsigned long);
    551 
    552 /* Set a field which starts at START and is LEN bits long.  DATA and
    553    TOTAL_LEN are the thing we are extracting it from, in byteorder ORDER.  */
    554 static void
    555 put_field (unsigned char *data, enum floatformat_byteorders order,
    556            unsigned int total_len, unsigned int start, unsigned int len,
    557            unsigned long stuff_to_put)
    558 {
    559   unsigned int cur_byte;
    560   int lo_bit, hi_bit;
    561   int nextbyte = (order == floatformat_little) ? 1 : -1;
    562 
    563   /* Start is in big-endian bit order!  Fix that first.  */
    564   start = total_len - (start + len);
    565 
    566   /* Start at the least significant part of the field.  */
    567   if (order == floatformat_little)
    568     cur_byte = start / FLOATFORMAT_CHAR_BIT;
    569   else
    570     cur_byte = (total_len - start - 1) / FLOATFORMAT_CHAR_BIT;
    571 
    572   lo_bit = start % FLOATFORMAT_CHAR_BIT;
    573   hi_bit = min (lo_bit + len, FLOATFORMAT_CHAR_BIT);
    574 
    575   do
    576     {
    577       unsigned char *byte_ptr = data + cur_byte;
    578       unsigned int bits = hi_bit - lo_bit;
    579       unsigned int mask = ((1 << bits) - 1) << lo_bit;
    580       *byte_ptr = (*byte_ptr & ~mask) | ((stuff_to_put << lo_bit) & mask);
    581       stuff_to_put >>= bits;
    582       len -= bits;
    583       cur_byte += nextbyte;
    584       lo_bit = 0;
    585       hi_bit = min (len, FLOATFORMAT_CHAR_BIT);
    586     }
    587   while (len != 0);
    588 }
    589 
    590 /* The converse: convert the double *FROM to an extended float
    591    and store where TO points.  Neither FROM nor TO have any alignment
    592    restrictions.  */
    593 
    594 void
    595 floatformat_from_double (const struct floatformat *fmt,
    596                          const double *from, void *to)
    597 {
    598   double dfrom;
    599   int exponent;
    600   double mant;
    601   unsigned int mant_bits, mant_off;
    602   int mant_bits_left;
    603   unsigned char *uto = (unsigned char *) to;
    604 
    605   dfrom = *from;
    606   memset (uto, 0, fmt->totalsize / FLOATFORMAT_CHAR_BIT);
    607 
    608   /* Split values are not handled specially, since a bottom half of
    609      zero is correct for any value representable as double (in the
    610      only supported case of split values).  */
    611 
    612   /* If negative, set the sign bit.  */
    613   if (dfrom < 0)
    614     {
    615       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->sign_start, 1, 1);
    616       dfrom = -dfrom;
    617     }
    618 
    619   if (dfrom == 0)
    620     {
    621       /* 0.0.  */
    622       return;
    623     }
    624 
    625   if (dfrom != dfrom)
    626     {
    627       /* NaN.  */
    628       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    629 		 fmt->exp_len, fmt->exp_nan);
    630       /* Be sure it's not infinity, but NaN value is irrelevant.  */
    631       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->man_start,
    632 		 32, 1);
    633       return;
    634     }
    635 
    636   if (dfrom + dfrom == dfrom)
    637     {
    638       /* This can only happen for an infinite value (or zero, which we
    639 	 already handled above).  */
    640       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    641 		 fmt->exp_len, fmt->exp_nan);
    642       return;
    643     }
    644 
    645   mant = frexp (dfrom, &exponent);
    646   if (exponent + fmt->exp_bias - 1 > 0)
    647     put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    648 	       fmt->exp_len, exponent + fmt->exp_bias - 1);
    649   else
    650     {
    651       /* Handle a denormalized number.  FIXME: What should we do for
    652 	 non-IEEE formats?  */
    653       put_field (uto, fmt->byteorder, fmt->totalsize, fmt->exp_start,
    654 		 fmt->exp_len, 0);
    655       mant = ldexp (mant, exponent + fmt->exp_bias - 1);
    656     }
    657 
    658   mant_bits_left = fmt->man_len;
    659   mant_off = fmt->man_start;
    660   while (mant_bits_left > 0)
    661     {
    662       unsigned long mant_long;
    663       mant_bits = mant_bits_left < 32 ? mant_bits_left : 32;
    664 
    665       mant *= 4294967296.0;
    666       mant_long = (unsigned long)mant;
    667       mant -= mant_long;
    668 
    669       /* If the integer bit is implicit, and we are not creating a
    670 	 denormalized number, then we need to discard it.  */
    671       if ((unsigned int) mant_bits_left == fmt->man_len
    672 	  && fmt->intbit == floatformat_intbit_no
    673 	  && exponent + fmt->exp_bias - 1 > 0)
    674 	{
    675 	  mant_long &= 0x7fffffff;
    676 	  mant_bits -= 1;
    677 	}
    678       else if (mant_bits < 32)
    679 	{
    680 	  /* The bits we want are in the most significant MANT_BITS bits of
    681 	     mant_long.  Move them to the least significant.  */
    682 	  mant_long >>= 32 - mant_bits;
    683 	}
    684 
    685       put_field (uto, fmt->byteorder, fmt->totalsize,
    686 		 mant_off, mant_bits, mant_long);
    687       mant_off += mant_bits;
    688       mant_bits_left -= mant_bits;
    689     }
    690 }
    691 
    692 /* Return non-zero iff the data at FROM is a valid number in format FMT.  */
    693 
    694 int
    695 floatformat_is_valid (const struct floatformat *fmt, const void *from)
    696 {
    697   return fmt->is_valid (fmt, from);
    698 }
    699 
    700 
    701 #ifdef IEEE_DEBUG
    702 
    703 #include <stdio.h>
    704 
    705 /* This is to be run on a host which uses IEEE floating point.  */
    706 
    707 void
    708 ieee_test (double n)
    709 {
    710   double result;
    711 
    712   floatformat_to_double (&floatformat_ieee_double_little, &n, &result);
    713   if ((n != result && (! isnan (n) || ! isnan (result)))
    714       || (n < 0 && result >= 0)
    715       || (n >= 0 && result < 0))
    716     printf ("Differ(to): %.20g -> %.20g\n", n, result);
    717 
    718   floatformat_from_double (&floatformat_ieee_double_little, &n, &result);
    719   if ((n != result && (! isnan (n) || ! isnan (result)))
    720       || (n < 0 && result >= 0)
    721       || (n >= 0 && result < 0))
    722     printf ("Differ(from): %.20g -> %.20g\n", n, result);
    723 
    724 #if 0
    725   {
    726     char exten[16];
    727 
    728     floatformat_from_double (&floatformat_m68881_ext, &n, exten);
    729     floatformat_to_double (&floatformat_m68881_ext, exten, &result);
    730     if (n != result)
    731       printf ("Differ(to+from): %.20g -> %.20g\n", n, result);
    732   }
    733 #endif
    734 
    735 #if IEEE_DEBUG > 1
    736   /* This is to be run on a host which uses 68881 format.  */
    737   {
    738     long double ex = *(long double *)exten;
    739     if (ex != n)
    740       printf ("Differ(from vs. extended): %.20g\n", n);
    741   }
    742 #endif
    743 }
    744 
    745 int
    746 main (void)
    747 {
    748   ieee_test (0.0);
    749   ieee_test (0.5);
    750   ieee_test (1.1);
    751   ieee_test (256.0);
    752   ieee_test (0.12345);
    753   ieee_test (234235.78907234);
    754   ieee_test (-512.0);
    755   ieee_test (-0.004321);
    756   ieee_test (1.2E-70);
    757   ieee_test (1.2E-316);
    758   ieee_test (4.9406564584124654E-324);
    759   ieee_test (- 4.9406564584124654E-324);
    760   ieee_test (- 0.0);
    761   ieee_test (- INFINITY);
    762   ieee_test (- NAN);
    763   ieee_test (INFINITY);
    764   ieee_test (NAN);
    765   return 0;
    766 }
    767 #endif
    768