gnulib/lib/logb.c

/* Floating-point exponent.
   Copyright (C) 2012-2020 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/>.  */

#if ! (defined USE_LONG_DOUBLE || defined USE_FLOAT)
# include <config.h>
#endif

/* Specification.  */
#include <math.h>

#ifdef USE_LONG_DOUBLE
# define LOGB logbl
# define DOUBLE long double
# define L_(literal) literal##L
# define HUGEVAL HUGE_VALL
# define FREXP frexpl
# define ISNAN isnanl
#elif ! defined USE_FLOAT
# define LOGB logb
# define DOUBLE double
# define L_(literal) literal
# define HUGEVAL HUGE_VAL
# define FREXP frexp
# define ISNAN isnand
#else /* defined USE_FLOAT */
# define LOGB logbf
# define DOUBLE float
# define L_(literal) literal##f
# define HUGEVAL HUGE_VALF
# define FREXP frexpf
# define ISNAN isnanf
#endif

DOUBLE
LOGB (DOUBLE x)
{
  if (isfinite (x))
    {
      if (x == L_(0.0))
        /* Return -Infinity.  */
        return - HUGEVAL;
      else
        {
          int e;

          (void) FREXP (x, &e);
          return (DOUBLE) (e - 1);
        }
    }
  else
    {
      if (ISNAN (x))
        return x; /* NaN */
      else
        /* Return +Infinity.  */
        return HUGEVAL;
    }
}