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. */
20 #if !(defined USE_LONG_DOUBLE && !HAVE_LONG_DOUBLE)
26 # ifdef USE_LONG_DOUBLE
27 # include "isnanl-nolibm.h"
32 /* This file assumes FLT_RADIX = 2. If FLT_RADIX is a power of 2 greater
33 than 2, or not even a power of 2, some rounding errors can occur, so that
34 then the returned mantissa is only guaranteed to be <= 1.0, not < 1.0. */
36 # ifdef USE_LONG_DOUBLE
38 # define DOUBLE long double
40 # define L_(literal) literal##L
43 # define DOUBLE double
45 # define L_(literal) literal
49 FUNC (DOUBLE x, int *exp)
54 /* Test for NaN, infinity, and zero. */
55 if (ISNAN (x) || x + x == x)
70 /* Implementation contributed by Paolo Bonzini.
71 Disabled because it's under GPL and doesn't pass the tests. */
73 /* Since the exponent is an 'int', it fits in 64 bits. Therefore the
74 loops are executed no more than 64 times. */
82 for (next = exponents, exponents[0] = L_(2.0), bit = 1;
84 bit <<= 1, next[1] = next[0] * next[0], next++);
86 for (; next >= exponents; bit >>= 1, next--)
95 for (next = exponents, exponents[0] = L_(0.5), bit = 1;
97 bit <<= 1, next[1] = next[0] * next[0], next++);
99 for (; next >= exponents; bit >>= 1, next--)
105 exponent = - exponent;
110 /* Implementation contributed by Bruno Haible. */
112 /* Since the exponent is an 'int', it fits in 64 bits. Therefore the
113 loops are executed no more than 64 times. */
114 DOUBLE pow2[64]; /* pow2[i] = 2^2^i */
115 DOUBLE powh[64]; /* powh[i] = 2^-2^i */
121 /* A positive exponent. */
122 DOUBLE pow2_i; /* = pow2[i] */
123 DOUBLE powh_i; /* = powh[i] */
125 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
126 x * 2^exponent = argument, x >= 1.0. */
127 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
129 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
133 exponent += (1 << i);
142 /* Avoid making x too small, as it could become a denormalized
143 number and thus lose precision. */
144 while (i > 0 && x < pow2[i - 1])
149 exponent += (1 << i);
151 /* Here 2^-2^i <= x < 1.0. */
155 /* A negative or zero exponent. */
156 DOUBLE pow2_i; /* = pow2[i] */
157 DOUBLE powh_i; /* = powh[i] */
159 /* Invariants: pow2_i = 2^2^i, powh_i = 2^-2^i,
160 x * 2^exponent = argument, x < 1.0. */
161 for (i = 0, pow2_i = L_(2.0), powh_i = L_(0.5);
163 i++, pow2_i = pow2_i * pow2_i, powh_i = powh_i * powh_i)
167 exponent -= (1 << i);
176 /* Here 2^-2^i <= x < 1.0. */
179 /* Invariants: x * 2^exponent = argument, and 2^-2^i <= x < 1.0. */
185 exponent -= (1 << i);
189 /* Here 0.5 <= x < 1.0. */
193 return (sign < 0 ? - x : x);
198 /* This declaration is solely to ensure that after preprocessing
199 this file is never empty. */