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[thirdparty/glibc.git] / sysdeps / ieee754 / dbl-64 / wordsize-64 / s_logb.c

/* Compute radix independent exponent.
   Copyright (C) 2011-2014 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <math.h>

#include <math_private.h>


double
__logb (double x)
{
  int64_t ix, ex;

  EXTRACT_WORDS64 (ix, x);
  ix &= UINT64_C(0x7fffffffffffffff);
  if (ix == 0)
    return -1.0 / fabs (x);
  ex = ix >> 52;
  if (ex == 0x7ff)
    return x * x;
  if (__builtin_expect (ex == 0, 0))
    {
      int m = __builtin_clzll (ix);
      ex -= m - 12;
    }
  return (double) (ex - 1023);
}
weak_alias (__logb, logb)
#ifdef NO_LONG_DOUBLE
strong_alias (__logb, __logbl)
weak_alias (__logb, logbl)
#endif