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. */
21 #include "ieee-float.h"
22 #include <math.h> /* ldexp */
24 /* Convert an IEEE extended float to a double.
25 FROM is the address of the extended float.
26 Store the double in *TO. */
29 ieee_extended_to_double (ext_format
, from
, to
)
30 const struct ext_format
*ext_format
;
34 unsigned char *ufrom
= (unsigned char *)from
;
36 unsigned long mant0
, mant1
, exponent
;
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
];
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. */
52 if (exponent
== 0 && mant0
== 0 && mant1
== 0) {
55 /* Build the result algebraically. Might go infinite, underflow, etc;
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. */
66 /* The converse: convert the double *FROM to an extended float
67 and store where TO points. */
70 double_to_ieee_extended (ext_format
, from
, to
)
71 const struct ext_format
*ext_format
;
76 unsigned long twolongs
[2];
77 unsigned long mant0
, mant1
, exponent
;
78 unsigned char tobytes
[8];
80 memset (to
, 0, TOTALSIZE
);
82 return; /* Result is zero */
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 */
91 to
[SIGNBYTE
] |= SIGNMASK
; /* Set negative sign */
92 /* How to tell an infinity from an ordinary number? FIXME-someday */
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);
103 exponent
= ((tobytes
[6] & 0xF0) >> 4) | (tobytes
[7] & 0x7F) << 4;
104 mant0
= (twolongs
[1] << 11) | twolongs
[0] >> 21;
105 mant1
= (twolongs
[0] << 11);
108 /* Fiddle with leading 1-bit, implied in double, explicit in extended. */
114 exponent
-= DBL_EXP_BIAS
; /* Get integer exp */
115 exponent
+= EXT_EXP_BIAS
; /* Offset for extended */
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
;
121 memcpy (&to
[MANBYTE_H
], &mant0
, 4);
122 memcpy (&to
[MANBYTE_L
], &mant1
, 4);
128 /* Test some numbers to see that extended/double conversion works for them. */
133 union { double d
; int i
[2]; } di
;
137 extern struct ext_format ext_format_68881
;
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
);
145 printf ("Differ: %x %x %g => %x %x %g\n", di
.d
, di
.d
, result
, result
);