gdb/ieee-float.c

   1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
   2    Copyright (C) 1991 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., 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20 #include "defs.h"
  21 #include "ieee-float.h"
  22 #include <math.h>               /* ldexp */
  23
  24 /* Convert an IEEE extended float to a double.
  25    FROM is the address of the extended float.
  26    Store the double in *TO.  */
  27
  28 void
  29 ieee_extended_to_double (ext_format, from, to)
  30      const struct ext_format *ext_format;
  31      char *from;
  32      double *to;
  33 {
  34   unsigned char *ufrom = (unsigned char *)from;
  35   double dto;
  36   unsigned long mant0, mant1, exponent;
  37
  38   memcpy (&mant0, &from[MANBYTE_H], 4);
  39   memcpy (&mant1, &from[MANBYTE_L], 4);
  40   exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L];
  41
  42 #if 0
  43   /* We can't do anything useful with a NaN anyway, so ignore its
  44      difference.  It will end up as Infinity or something close.  */
  45   if (exponent == EXT_EXP_NAN) {
  46     /* We have a NaN source.  */
  47     dto = 0.123456789;  /* Not much else useful to do -- we don't know if
  48                            the host system even *has* NaNs, nor how to
  49                            generate an innocuous one if it does.  */
  50   } else
  51 #endif
  52          if (exponent == 0 && mant0 == 0 && mant1 == 0) {
  53     dto = 0;
  54   } else {
  55     /* Build the result algebraically.  Might go infinite, underflow, etc;
  56        who cares. */
  57     mant0 |= 0x80000000;
  58     dto = ldexp  ((double)mant0, exponent - EXT_EXP_BIAS - 31);
  59     dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32);
  60     if (ufrom[EXPBYTE_H] & SIGNMASK)    /* If negative... */
  61       dto = -dto;                       /* ...negate.  */
  62   }
  63   *to = dto;
  64 }
  65
  66 /* The converse: convert the double *FROM to an extended float
  67    and store where TO points.  */
  68
  69 void
  70 double_to_ieee_extended (ext_format, from, to)
  71      const struct ext_format *ext_format;
  72      double *from;
  73      char *to;
  74 {
  75   double dfrom = *from;
  76   unsigned long twolongs[2];
  77   unsigned long mant0, mant1, exponent;
  78   unsigned char tobytes[8];
  79
  80   memset (to, 0, TOTALSIZE);
  81   if (dfrom == 0)
  82     return;                     /* Result is zero */
  83   if (dfrom != dfrom) {
  84     /* From is NaN */
  85     to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
  86     to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
  87     to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
  88     return;                     /* Result is NaN */
  89   }
  90   if (dfrom < 0)
  91     to[SIGNBYTE] |= SIGNMASK;   /* Set negative sign */
  92   /* How to tell an infinity from an ordinary number?  FIXME-someday */
  93
  94   /* The following code assumes that the host has IEEE doubles.  FIXME-someday.
  95      It also assumes longs are 32 bits!  FIXME-someday.  */
  96   memcpy (twolongs, from, 8);
  97   memcpy (tobytes, from, 8);
  98 #if HOST_BYTE_ORDER == BIG_ENDIAN
  99   exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4;
 100   mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
 101   mant1 = (twolongs[1] << 11);
 102 #else
 103   exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4;
 104   mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
 105   mant1 = (twolongs[0] << 11);
 106 #endif
 107
 108   /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
 109   if (exponent == 0)
 110     mant0 &= 0x7FFFFFFF;
 111   else
 112     mant0 |= 0x80000000;
 113
 114   exponent -= DBL_EXP_BIAS;                             /* Get integer exp */
 115   exponent += EXT_EXP_BIAS;                             /* Offset for extended */
 116
 117   /* OK, now store it in extended format. */
 118   to[EXPBYTE_H] |= (unsigned char)(exponent >> 8);      /* Retain sign */
 119   to[EXPBYTE_L] =  (unsigned char) exponent;
 120
 121   memcpy (&to[MANBYTE_H], &mant0, 4);
 122   memcpy (&to[MANBYTE_L], &mant1, 4);
 123 }
 124
 125
 126 #ifdef IEEE_DEBUG
 127
 128 /* Test some numbers to see that extended/double conversion works for them.  */
 129
 130 ieee_test (n)
 131      int n;
 132 {
 133   union { double d; int i[2]; } di;
 134   double result;
 135   int i;
 136   char exten[16];
 137   extern struct ext_format ext_format_68881;
 138
 139   for (i = 0; i < n; i++) {
 140     di.i[0] = (random() << 16) | (random() & 0xffff);
 141     di.i[1] = (random() << 16) | (random() & 0xffff);
 142     double_to_ieee_extended (&ext_format_68881, &di.d, exten);
 143     ieee_extended_to_double (&ext_format_68881, exten, &result);
 144     if (di.d != result)
 145       printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
 146   }
 147 }
 148
 149 #endif