1 /* signbit() macro: Determine the sign bit of a floating-point number.
2 Copyright (C) 2007-2008 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/>. */
23 #include "isnand-nolibm.h"
29 gl_signbitd (double arg)
31 #if defined DBL_SIGNBIT_WORD && defined DBL_SIGNBIT_BIT
32 /* The use of a union to extract the bits of the representation of a
33 'long double' is safe in practice, despite of the "aliasing rules" of
34 C99, because the GCC docs say
35 "Even with '-fstrict-aliasing', type-punning is allowed, provided the
36 memory is accessed through the union type."
37 and similarly for other compilers. */
39 ((sizeof (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
40 union { double value; unsigned int word[NWORDS]; } m;
42 return (m.word[DBL_SIGNBIT_WORD] >> DBL_SIGNBIT_BIT) & 1;
43 #elif HAVE_COPYSIGN_IN_LIBC
44 return copysign (1.0, arg) < 0;
46 /* This does not do the right thing for NaN, but this is irrelevant for
54 /* Distinguish 0.0 and -0.0. */
55 static double plus_zero = 0.0;
57 return (memcmp (&plus_zero, &arg_mem, SIZEOF_DBL) != 0);