1 /* Split a double into fraction and mantissa.
2 Copyright (C) 2007-2012 Free Software Foundation, Inc.
4 This program is free software: you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 3 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program. If not, see <http://www.gnu.org/licenses/>. */
17 /* Written by Paolo Bonzini <bonzini@gnu.org>, 2003, and
18 Bruno Haible <bruno@clisp.org>, 2007. */
20 #if ! defined USE_LONG_DOUBLE
28 #ifdef USE_LONG_DOUBLE
29 # include "isnanl-nolibm.h"
32 # include "isnand-nolibm.h"
35 /* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater
36 than 2, or not even a power of 2, some rounding errors can occur, so that
37 then the returned mantissa is only guaranteed to be <= 1.0, not < 1.0. */
39 #ifdef USE_LONG_DOUBLE
41 # define DOUBLE long double
43 # define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
44 # define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
45 # define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
46 # define L_(literal) literal##L
49 # define DOUBLE double
51 # define DECL_ROUNDING
52 # define BEGIN_ROUNDING()
53 # define END_ROUNDING()
54 # define L_(literal) literal
58 FUNC (DOUBLE x
, int *expptr
)
64 /* Test for NaN, infinity, and zero. */
65 if (ISNAN (x
) || x
+ x
== x
)
81 /* Since the exponent is an 'int', it fits in 64 bits. Therefore the
82 loops are executed no more than 64 times. */
83 DOUBLE pow2
[64]; /* pow2[i] = 2^2^i */
84 DOUBLE powh
[64]; /* powh[i] = 2^-2^i */
90 /* A positive exponent. */
91 DOUBLE pow2_i
; /* = pow2[i] */
92 DOUBLE powh_i
; /* = powh[i] */
94 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
95 x * 2^exponent = argument, x >= 1.0. */
96 for (i
= 0, pow2_i
= L_(2.0), powh_i
= L_(0.5);
98 i
++, pow2_i
= pow2_i
* pow2_i
, powh_i
= powh_i
* powh_i
)
102 exponent
+= (1 << i
);
111 /* Avoid making x too small, as it could become a denormalized
112 number and thus lose precision. */
113 while (i
> 0 && x
< pow2
[i
- 1])
118 exponent
+= (1 << i
);
120 /* Here 2^-2^i <= x < 1.0. */
124 /* A negative or zero exponent. */
125 DOUBLE pow2_i
; /* = pow2[i] */
126 DOUBLE powh_i
; /* = powh[i] */
128 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
129 x * 2^exponent = argument, x < 1.0. */
130 for (i
= 0, pow2_i
= L_(2.0), powh_i
= L_(0.5);
132 i
++, pow2_i
= pow2_i
* pow2_i
, powh_i
= powh_i
* powh_i
)
136 exponent
-= (1 << i
);
145 /* Here 2^-2^i <= x < 1.0. */
148 /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0. */
154 exponent
-= (1 << i
);
158 /* Here 0.5 <= x < 1.0. */
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