1 /* IEEE floating point support routines, for GDB, the GNU Debugger.
2 Copyright (C) 1991 Free Software Foundation, Inc.
4 This file is part of GDB.
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.
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.
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. */
23 #include "ieee-float.h"
24 #include <math.h> /* ldexp */
26 /* Convert an IEEE extended float to a double.
27 FROM is the address of the extended float.
28 Store the double in *TO. */
31 ieee_extended_to_double (ext_format
, from
, to
)
32 const struct ext_format
*ext_format
;
36 unsigned char *ufrom
= (unsigned char *)from
;
38 unsigned long mant0
, mant1
, exponent
;
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
];
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. */
54 if (exponent
== 0 && mant0
== 0 && mant1
== 0) {
57 /* Build the result algebraically. Might go infinite, underflow, etc;
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. */
68 /* The converse: convert the double *FROM to an extended float
69 and store where TO points. */
72 double_to_ieee_extended (ext_format
, from
, to
)
73 const struct ext_format
*ext_format
;
78 unsigned long twolongs
[2];
79 unsigned long mant0
, mant1
, exponent
;
80 unsigned char tobytes
[8];
82 bzero (to
, TOTALSIZE
);
84 return; /* Result is zero */
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 */
93 to
[SIGNBYTE
] |= SIGNMASK
; /* Set negative sign */
94 /* How to tell an infinity from an ordinary number? FIXME-someday */
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);
105 exponent
= ((tobytes
[6] & 0xF0) >> 4) | (tobytes
[7] & 0x7F) << 4;
106 mant0
= (twolongs
[1] << 11) | twolongs
[0] >> 21;
107 mant1
= (twolongs
[0] << 11);
110 /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
116 exponent
-= DBL_EXP_BIAS
; /* Get integer exp */
117 exponent
+= EXT_EXP_BIAS
; /* Offset for extended */
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
;
123 memcpy (&to
[MANBYTE_H
], &mant0
, 4);
124 memcpy (&to
[MANBYTE_L
], &mant1
, 4);
130 /* Test some numbers to see that extended/double conversion works for them. */
135 union { double d
; int i
[2]; } di
;
139 extern struct ext_format ext_format_68881
;
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
);
147 printf ("Differ: %x %x %g => %x %x %g\n", di
.d
, di
.d
, result
, result
);