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 (exp == EXT_EXP_NAN) {
  44     /* We have a NaN source.  */
  45     dto = 0.123456789;  /* Not much else useful to do */
  46   } else if (exp == 0 && mant0 == 0 && mant1 == 0) {
  47     dto = 0;
  48   } else {
  49     /* Build the result algebraically.  Might go infinite, underflow, etc;
  50        who cares. */
  51     mant0 |= 0x80000000;
  52     dto = ldexp  ((double)mant0, exp - EXT_EXP_BIAS - 31);
  53     dto += ldexp ((double)mant1, exp - EXT_EXP_BIAS - 31 - 32);
  54   }
  55   *to = dto;
  56 }
  57
  58 /* The converse: convert the double *FROM to an extended float
  59    and store where TO points.  */
  60
  61 void
  62 double_to_ieee_extended (ext_format, from, to)
  63      struct ext_format *ext_format;
  64      double *from;
  65      char *to;
  66 {
  67   double dfrom = *from;
  68   unsigned long twolongs[2];
  69   unsigned long mant0, mant1, exp;
  70   unsigned char twobytes[2];
  71
  72   bzero (to, TOTALSIZE);
  73   if (dfrom == 0)
  74     return;                     /* Result is zero */
  75   if (dfrom != dfrom) {
  76     /* From is NaN */
  77     to[EXPBYTE_H] = (unsigned char)(EXT_EXP_NAN >> 8);
  78     to[EXPBYTE_L] = (unsigned char)EXT_EXP_NAN;
  79     to[MANBYTE_H] = 1; /* Be sure it's not infinity, but NaN value is irrel */
  80     return;                     /* Result is NaN */
  81   }
  82   if (dfrom < 0)
  83     to[SIGNBYTE] |= SIGNMASK;   /* Set negative sign */
  84   /* How to tell an infinity from an ordinary number?  FIXME-someday */
  85
  86   /* The following code assumes that the host has IEEE doubles.  FIXME-someday.
  87      It also assumes longs are 32 bits!  FIXME-someday.  */
  88   bcopy (from, twolongs, 8);
  89   bcopy (from, twobytes, 2);
  90 #if HOST_BYTE_ORDER == BIG_ENDIAN
  91   exp = ((twobytes[1] & 0xF0) >> 4) | (twobytes[0] & 0x7F) << 4;
  92   mant0 = (twolongs[0] << 11) | twolongs[1] >> 21;
  93   mant1 = (twolongs[1] << 11);
  94 #else
  95   exp = ((twobytes[0] & 0xF0) >> 4) | (twobytes[1] & 0x7F) << 4;
  96   mant0 = (twolongs[1] << 11) | twolongs[0] >> 21;
  97   mant1 = (twolongs[0] << 11);
  98 #endif
  99
 100   /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
 101   if (exp == 0)
 102     mant0 &= 0x7FFFFFFF;
 103   else
 104     mant0 |= 0x80000000;
 105
 106   exp -= DBL_EXP_BIAS;                          /* Get integer exp */
 107   exp += EXT_EXP_BIAS;                          /* Offset for extended *&/
 108
 109   /* OK, now store it in extended format. */
 110   to[EXPBYTE_H] |= (unsigned char)(exp >> 8);   /* Retain sign */
 111   to[EXPBYTE_L] =  (unsigned char) exp;
 112
 113   bcopy (&mant0, &to[MANBYTE_H], 4);
 114   bcopy (&mant1, &to[MANBYTE_L], 4);
 115 }
 116
 117
 118 #ifdef DEBUG
 119
 120 /* Test some numbers to see that extended/double conversion works for them.  */
 121
 122 ieee_test (n)
 123      int n;
 124 {
 125   union { double d; int i[2]; } di;
 126   double result;
 127   int i;
 128   char exten[16];
 129   extern struct ext_format ext_format_68881;
 130
 131   for (i = 0; i < n; i++) {
 132     di.i[0] = random();
 133     di.i[1] = random();
 134     double_to_ieee_extended (ext_format_68881, &di.d, exten);
 135     ieee_extended_to_double (ext_format_68881, exten, &result);
 136     if (di.d != result)
 137       printf ("Differ: %x %x %g => %x %x %g\n", di.d, di.d, result, result);
 138   }
 139 }
 140
 141 #endif