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 <stdio.h>
  21
  22 #include "defs.h"
  23 #include "ieee-float.h"
  24 #include <math.h>               /* ldexp */
  25
  26 /* Convert an IEEE extended float to a double.
  27    FROM is the address of the extended float.
  28    Store the double in *TO.  */
  29
  30 void
  31 ieee_extended_to_double (ext_format, from, to)
  32      const struct ext_format *ext_format;
  33      char *from;
  34      double *to;
  35 {
  36   unsigned char *ufrom = (unsigned char *)from;
  37   double dto;
  38   unsigned long mant0, mant1, exponent;
  39
  40   memcpy (&mant0, &from[MANBYTE_H], 4);
  41   memcpy (&mant1, &from[MANBYTE_L], 4);
  42   exponent = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L];
  43
  44 #if 0
  45   /* We can't do anything useful with a NaN anyway, so ignore its
  46      difference.  It will end up as Infinity or something close.  */
  47   if (exponent == EXT_EXP_NAN) {
  48     /* We have a NaN source.  */
  49     dto = 0.123456789;  /* Not much else useful to do -- we don't know if
  50                            the host system even *has* NaNs, nor how to
  51                            generate an innocuous one if it does.  */
  52   } else
  53 #endif
  54          if (exponent == 0 && mant0 == 0 && mant1 == 0) {
  55     dto = 0;
  56   } else {
  57     /* Build the result algebraically.  Might go infinite, underflow, etc;
  58        who cares. */
  59     mant0 |= 0x80000000;
  60     dto = ldexp  ((double)mant0, exponent - EXT_EXP_BIAS - 31);
  61     dto += ldexp ((double)mant1, exponent - EXT_EXP_BIAS - 31 - 32);
  62     if (ufrom[EXPBYTE_H] & SIGNMASK)    /* If negative... */
  63       dto = -dto;                       /* ...negate.  */
  64   }
  65   *to = dto;
  66 }
  67
  68 /* The converse: convert the double *FROM to an extended float
  69    and store where TO points.  */
  70
  71 void
  72 double_to_ieee_extended (ext_format, from, to)
  73      const struct ext_format *ext_format;
  74      double *from;
  75      char *to;
  76 {
  77   double dfrom = *from;
  78   unsigned long twolongs[2];
  79   unsigned long mant0, mant1, exponent;
  80   unsigned char tobytes[8];
  81
  82   bzero (to, TOTALSIZE);
  83   if (dfrom == 0)
  84     return;                     /* Result is zero */
  85   if (dfrom != dfrom) {
  86     /* From is NaN */
  87     to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
  88     to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
  89     to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
  90     return;                     /* Result is NaN */
  91   }
  92   if (dfrom < 0)
  93     to[SIGNBYTE] |= SIGNMASK;   /* Set negative sign */
  94   /* How to tell an infinity from an ordinary number?  FIXME-someday */
  95
  96   /* The following code assumes that the host has IEEE doubles.  FIXME-someday.
  97      It also assumes longs are 32 bits!  FIXME-someday.  */
  98   memcpy (twolongs, from, 8);
  99   memcpy (tobytes, from, 8);
 100 #if HOST_BYTE_ORDER == BIG_ENDIAN
 101   exponent = ((tobytes[1] & 0xF0) >> 4) | (tobytes[0] & 0x7F) << 4;
 102   mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
 103   mant1 = (twolongs[1] << 11);
 104 #else
 105   exponent = ((tobytes[6] & 0xF0) >> 4) | (tobytes[7] & 0x7F) << 4;
 106   mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
 107   mant1 = (twolongs[0] << 11);
 108 #endif
 109
 110   /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
 111   if (exponent == 0)
 112     mant0 &= 0x7FFFFFFF;
 113   else
 114     mant0 |= 0x80000000;
 115
 116   exponent -= DBL_EXP_BIAS;                             /* Get integer exp */
 117   exponent += EXT_EXP_BIAS;                             /* Offset for extended */
 118
 119   /* OK, now store it in extended format. */
 120   to[EXPBYTE_H] |= (unsigned char)(exponent >> 8);      /* Retain sign */
 121   to[EXPBYTE_L] =  (unsigned char) exponent;
 122
 123   memcpy (&to[MANBYTE_H], &mant0, 4);
 124   memcpy (&to[MANBYTE_L], &mant1, 4);
 125 }
 126
 127
 128 #ifdef IEEE_DEBUG
 129
 130 /* Test some numbers to see that extended/double conversion works for them.  */
 131
 132 ieee_test (n)
 133      int n;
 134 {
 135   union { double d; int i[2]; } di;
 136   double result;
 137   int i;
 138   char exten[16];
 139   extern struct ext_format ext_format_68881;
 140
 141   for (i = 0; i < n; i++) {
 142     di.i[0] = (random() << 16) | (random() & 0xffff);
 143     di.i[1] = (random() << 16) | (random() & 0xffff);
 144     double_to_ieee_extended (&ext_format_68881, &di.d, exten);
 145     ieee_extended_to_double (&ext_format_68881, exten, &result);
 146     if (di.d != result)
 147       printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
 148   }
 149 }
 150
 151 #endif