math/w_log2.c

   1 /* Copyright (C) 2011-2015 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <fenv.h>
  20 #include <math.h>
  21 #include <math_private.h>
  22
  23
  24 /* wrapper log2(x) */
  25 double
  26 __log2 (double x)
  27 {
  28   if (__builtin_expect (islessequal (x, 0.0), 0) && _LIB_VERSION != _IEEE_)
  29     {
  30       if (x == 0.0)
  31         {
  32           feraiseexcept (FE_DIVBYZERO);
  33           return __kernel_standard (x, x, 48); /* log2(0) */
  34         }
  35       else
  36         {
  37           feraiseexcept (FE_INVALID);
  38           return __kernel_standard (x, x, 49); /* log2(x<0) */
  39         }
  40     }
  41
  42   return  __ieee754_log2 (x);
  43 }
  44 weak_alias (__log2, log2)
  45 #ifdef NO_LONG_DOUBLE
  46 strong_alias (__log2, __log2l)
  47 weak_alias (__log2, log2l)
  48 #endif