1 /* signbit() macro: Determine the sign bit of a floating-point number.
2 Copyright (C) 2007, 2009-2017 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 <https://www.gnu.org/licenses/>. */
23 #include "isnanf-nolibm.h"
26 #ifdef gl_signbitf_OPTIMIZED_MACRO
31 gl_signbitf (float arg
)
33 #if defined FLT_SIGNBIT_WORD && defined FLT_SIGNBIT_BIT
34 /* The use of a union to extract the bits of the representation of a
35 'long double' is safe in practice, despite of the "aliasing rules" of
36 C99, because the GCC docs say
37 "Even with '-fstrict-aliasing', type-punning is allowed, provided the
38 memory is accessed through the union type."
39 and similarly for other compilers. */
41 ((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
42 union { float value
; unsigned int word
[NWORDS
]; } m
;
44 return (m
.word
[FLT_SIGNBIT_WORD
] >> FLT_SIGNBIT_BIT
) & 1;
45 #elif HAVE_COPYSIGNF_IN_LIBC
46 return copysignf (1.0f
, arg
) < 0;
48 /* This does not do the right thing for NaN, but this is irrelevant for
56 /* Distinguish 0.0f and -0.0f. */
57 static float plus_zero
= 0.0f
;
59 return (memcmp (&plus_zero
, &arg_mem
, SIZEOF_FLT
) != 0);