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 GDB 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 1, or (at your option)
   9 any later version.
  10
  11 GDB 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 GDB; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */
  19
  20 #include "defs.h"
  21 #include "param.h"
  22 #include "ieee-float.h"
  23 #include <math.h>               /* ldexp */
  24
  25 /* Convert an IEEE extended float to a double.
  26    FROM is the address of the extended float.
  27    Store the double in *TO.  */
  28
  29 void
  30 ieee_extended_to_double (ext_format, from, to)
  31      struct ext_format *ext_format;
  32      char *from;
  33      double *to;
  34 {
  35   unsigned char *ufrom = (unsigned char *)from;
  36   double dto;
  37   unsigned long mant0, mant1, exp;
  38
  39   bcopy (&from[MANBYTE_H], &mant0, 4);
  40   bcopy (&from[MANBYTE_L], &mant1, 4);
  41   exp = ((ufrom[EXPBYTE_H] & (unsigned char)~SIGNMASK) << 8) | ufrom[EXPBYTE_L];
  42
  43 #if 0
  44   /* We can't do anything useful with a NaN anyway, so ignore its
  45      difference.  It will end up as Infinity or something close.  */
  46   if (exp == EXT_EXP_NAN) {
  47     /* We have a NaN source.  */
  48     dto = 0.123456789;  /* Not much else useful to do -- we don't know if
  49                            the host system even *has* NaNs, nor how to
  50                            generate an innocuous one if it does.  */
  51   } else
  52 #endif
  53          if (exp == 0 && mant0 == 0 && mant1 == 0) {
  54     dto = 0;
  55   } else {
  56     /* Build the result algebraically.  Might go infinite, underflow, etc;
  57        who cares. */
  58     mant0 |= 0x80000000;
  59     dto = ldexp  ((double)mant0, exp - EXT_EXP_BIAS - 31);
  60     dto += ldexp ((double)mant1, exp - EXT_EXP_BIAS - 31 - 32);
  61     if (ufrom[EXPBYTE_H] & SIGNMASK)    /* If negative... */
  62       dto = -dto;                       /* ...negate.  */
  63   }
  64   *to = dto;
  65 }
  66
  67 /* The converse: convert the double *FROM to an extended float
  68    and store where TO points.  */
  69
  70 void
  71 double_to_ieee_extended (ext_format, from, to)
  72      struct ext_format *ext_format;
  73      double *from;
  74      char *to;
  75 {
  76   double dfrom = *from;
  77   unsigned long twolongs[2];
  78   unsigned long mant0, mant1, exp;
  79   unsigned char twobytes[2];
  80
  81   bzero (to, TOTALSIZE);
  82   if (dfrom == 0)
  83     return;                     /* Result is zero */
  84   if (dfrom != dfrom) {
  85     /* From is NaN */
  86     to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
  87     to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
  88     to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
  89     return;                     /* Result is NaN */
  90   }
  91   if (dfrom < 0)
  92     to[SIGNBYTE] |= SIGNMASK;   /* Set negative sign */
  93   /* How to tell an infinity from an ordinary number?  FIXME-someday */
  94
  95   /* The following code assumes that the host has IEEE doubles.  FIXME-someday.
  96      It also assumes longs are 32 bits!  FIXME-someday.  */
  97   bcopy (from, twolongs, 8);
  98   bcopy (from, twobytes, 2);
  99 #if HOST_BYTE_ORDER == BIG_ENDIAN
 100   exp = ((twobytes[1] & 0xF0) >> 4) | (twobytes[0] & 0x7F) << 4;
 101   mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
 102   mant1 = (twolongs[1] << 11);
 103 #else
 104   exp = ((twobytes[0] & 0xF0) >> 4) | (twobytes[1] & 0x7F) << 4;
 105   mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
 106   mant1 = (twolongs[0] << 11);
 107 #endif
 108
 109   /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
 110   if (exp == 0)
 111     mant0 &= 0x7FFFFFFF;
 112   else
 113     mant0 |= 0x80000000;
 114
 115   exp -= DBL_EXP_BIAS;                          /* Get integer exp */
 116   exp += EXT_EXP_BIAS;                          /* Offset for extended *&/
 117
 118   /* OK, now store it in extended format. */
 119   to[EXPBYTE_H] |= (unsigned char)(exp >> 8);   /* Retain sign */
 120   to[EXPBYTE_L] =  (unsigned char) exp;
 121
 122   bcopy (&mant0, &to[MANBYTE_H], 4);
 123   bcopy (&mant1, &to[MANBYTE_L], 4);
 124 }
 125
 126
 127 #ifdef DEBUG
 128
 129 /* Test some numbers to see that extended/double conversion works for them.  */
 130
 131 ieee_test (n)
 132      int n;
 133 {
 134   union { double d; int i[2]; } di;
 135   double result;
 136   int i;
 137   char exten[16];
 138   extern struct ext_format ext_format_68881;
 139
 140   for (i = 0; i < n; i++) {
 141     di.i[0] = (random() << 16) | (random() & 0xffff);
 142     di.i[1] = (random() << 16) | (random() & 0xffff);
 143     double_to_ieee_extended (&ext_format_68881, &di.d, exten);
 144     ieee_extended_to_double (&ext_format_68881, exten, &result);
 145     if (di.d != result)
 146       printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
 147   }
 148 }
 149
 150 #endif