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