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/* signbit() macro: Determine the sign bit of a floating-point number.
Copyright (C) 2007 Free Software Foundation, Inc.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation,
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
#include <config.h>
/* Specification. */
#include <math.h>
#include <string.h>
#include "isnanf.h"
#include "float+.h"
#undef gl_signbitf
int
gl_signbitf (float arg)
{
#if defined FLT_SIGNBIT_WORD && defined FLT_SIGNBIT_BIT
/* The use of a union to extract the bits of the representation of a
'long double' is safe in practice, despite of the "aliasing rules" of
C99, because the GCC docs say
"Even with '-fstrict-aliasing', type-punning is allowed, provided the
memory is accessed through the union type."
and similarly for other compilers. */
# define NWORDS \
((sizeof (float) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
union { float value; unsigned int word[NWORDS]; } m;
m.value = arg;
return (m.word[FLT_SIGNBIT_WORD] >> FLT_SIGNBIT_BIT) & 1;
#elif HAVE_COPYSIGNF_IN_LIBC
return copysignf (1.0f, arg) < 0;
#else
/* This does not do the right thing for NaN, but this is irrelevant for
most use cases. */
if (isnanf (arg))
return 0;
if (arg < 0.0f)
return 1;
else if (arg == 0.0f)
{
/* Distinguish 0.0f and -0.0f. */
static float plus_zero = 0.0f;
float arg_mem = arg;
return (memcmp (&plus_zero, &arg_mem, SIZEOF_FLT) != 0);
}
else
return 0;
#endif
}
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