text: /* signbit() macro: Determine the sign bit of a floating-point number.
     Copyright (C) 2007, 2009-2012 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 <http://www.gnu.org/licenses/>.  */
  
  #include <config.h>
  
  /* Specification.  */
  #include <math.h>
  
  #include <string.h>
  #include "isnanl-nolibm.h"
  #include "float+.h"
  
  #ifdef gl_signbitl_OPTIMIZED_MACRO
  # undef gl_signbitl
  #endif
  
  int
  gl_signbitl (long double arg)
  {
  #if defined LDBL_SIGNBIT_WORD && defined LDBL_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 (long double) + sizeof (unsigned int) - 1) / sizeof (unsigned int))
    union { long double value; unsigned int word[NWORDS]; } m;
    m.value = arg;
    return (m.word[LDBL_SIGNBIT_WORD] >> LDBL_SIGNBIT_BIT) & 1;
  #elif HAVE_COPYSIGNL_IN_LIBC
    return copysignl (1.0L, arg) < 0;
  #else
    /* This does not do the right thing for NaN, but this is irrelevant for
       most use cases.  */
    if (isnanl (arg))
      return 0;
    if (arg < 0.0L)
      return 1;
    else if (arg == 0.0L)
      {
        /* Distinguish 0.0L and -0.0L.  */
        static long double plus_zero = 0.0L;
        long double arg_mem = arg;
        return (memcmp (&plus_zero, &arg_mem, SIZEOF_LDBL) != 0);
      }
    else
      return 0;
  #endif
  }
  