1 /* Split a double into fraction and mantissa.
2 Copyright (C) 2007-2010 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. */
26 #ifdef USE_LONG_DOUBLE
27 # include "isnanl-nolibm.h"
30 # include "isnand-nolibm.h"
33 /* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater
34 than 2, or not even a power of 2, some rounding errors can occur, so that
35 then the returned mantissa is only guaranteed to be <= 1.0, not < 1.0. */
37 #ifdef USE_LONG_DOUBLE
39 # define DOUBLE long double
41 # define DECL_ROUNDING DECL_LONG_DOUBLE_ROUNDING
42 # define BEGIN_ROUNDING() BEGIN_LONG_DOUBLE_ROUNDING ()
43 # define END_ROUNDING() END_LONG_DOUBLE_ROUNDING ()
44 # define L_(literal) literal##L
47 # define DOUBLE double
49 # define DECL_ROUNDING
50 # define BEGIN_ROUNDING()
51 # define END_ROUNDING()
52 # define L_(literal) literal
56 FUNC (DOUBLE x, int *expptr)
62 /* Test for NaN, infinity, and zero. */
63 if (ISNAN (x) || x + x == x)
79 /* Since the exponent is an 'int', it fits in 64 bits. Therefore the
80 loops are executed no more than 64 times. */
81 DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
82 DOUBLE powh[64]; /* powh[i] = 2^-2^i */
88 /* A positive exponent. */
89 DOUBLE pow2_i; /* = pow2[i] */
90 DOUBLE powh_i; /* = powh[i] */
92 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
93 x * 2^exponent = argument, x >= 1.0. */
94 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
96 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
100 exponent += (1 << i);
109 /* Avoid making x too small, as it could become a denormalized
110 number and thus lose precision. */
111 while (i > 0 && x < pow2[i - 1])
116 exponent += (1 << i);
118 /* Here 2^-2^i <= x < 1.0. */
122 /* A negative or zero exponent. */
123 DOUBLE pow2_i; /* = pow2[i] */
124 DOUBLE powh_i; /* = powh[i] */
126 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
127 x * 2^exponent = argument, x < 1.0. */
128 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
130 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
134 exponent -= (1 << i);
143 /* Here 2^-2^i <= x < 1.0. */
146 /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0. */
152 exponent -= (1 << i);
156 /* Here 0.5 <= x < 1.0. */