/* signbit() macro: Determine the sign bit of a floating-point number.

   Copyright (C) 2007-2018 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 3 of the License, 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, see <https://www.gnu.org/licenses/>.  */

#include <config.h>

/* Specification.  */

#include <math.h>

#include <string.h>

#include "isnand-nolibm.h"

#include "float+.h"

#ifdef gl_signbitd_OPTIMIZED_MACRO

# undef gl_signbitd

#endif

int

gl_signbitd (double arg)

{

#if defined DBL_SIGNBIT_WORD && defined DBL_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 (double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))

  union { double value; unsigned int word[NWORDS]; } m;

  m.value = arg;

  return (m.word[DBL_SIGNBIT_WORD] >> DBL_SIGNBIT_BIT) & 1;

#elif HAVE_COPYSIGN_IN_LIBC

  return copysign (1.0, arg) < 0;

#else

  /* This does not do the right thing for NaN, but this is irrelevant for

     most use cases.  */

  if (isnand (arg))

    return 0;

  if (arg < 0.0)

    return 1;

  else if (arg == 0.0)

    {

      /* Distinguish 0.0 and -0.0.  */

      static double plus_zero = 0.0;

      double arg_mem = arg;

      return (memcmp (&plus_zero, &arg_mem, SIZEOF_DBL) != 0);

    }

  else

    return 0;

#endif

}