1 /* Split a double into fraction and mantissa.
2 Copyright (C) 2007 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 2, or (at your option)
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 along
15 with this program; if not, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18 /* Written by Paolo Bonzini <bonzini@gnu.org>, 2003, and
19 Bruno Haible <bruno@clisp.org>, 2007. */
23 #if !(defined USE_LONG_DOUBLE && !HAVE_LONG_DOUBLE)
29 # ifdef USE_LONG_DOUBLE
30 # include "isnanl-nolibm.h"
36 /* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater
37 than 2, or not even a power of 2, some rounding errors can occur, so that
38 then the returned mantissa is only guaranteed to be <= 1.0, not < 1.0. */
40 # ifdef USE_LONG_DOUBLE
42 # define DOUBLE long double
44 # define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
45 # define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
46 # define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
47 # define L_(literal) literal##L
50 # define DOUBLE double
52 # define DECL_ROUNDING
53 # define BEGIN_ROUNDING()
54 # define END_ROUNDING()
55 # define L_(literal) literal
59 FUNC (DOUBLE x, int *exp)
65 /* Test for NaN, infinity, and zero. */
66 if (ISNAN (x) || x + x == x)
82 /* Since the exponent is an 'int', it fits in 64 bits. Therefore the
83 loops are executed no more than 64 times. */
84 DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
85 DOUBLE powh[64]; /* powh[i] = 2^-2^i */
91 /* A positive exponent. */
92 DOUBLE pow2_i; /* = pow2[i] */
93 DOUBLE powh_i; /* = powh[i] */
95 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
96 x * 2^exponent = argument, x >= 1.0. */
97 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
99 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
103 exponent += (1 << i);
112 /* Avoid making x too small, as it could become a denormalized
113 number and thus lose precision. */
114 while (i > 0 && x < pow2[i - 1])
119 exponent += (1 << i);
121 /* Here 2^-2^i <= x < 1.0. */
125 /* A negative or zero exponent. */
126 DOUBLE pow2_i; /* = pow2[i] */
127 DOUBLE powh_i; /* = powh[i] */
129 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
130 x * 2^exponent = argument, x < 1.0. */
131 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
133 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
137 exponent -= (1 << i);
146 /* Here 2^-2^i <= x < 1.0. */
149 /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0. */
155 exponent -= (1 << i);
159 /* Here 0.5 <= x < 1.0. */
173 /* This declaration is solely to ensure that after preprocessing
174 this file is never empty. */