libm/w_log2f.c

   1 /* Copyright (C) 2011-2016 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 <math.h>
  20 #include "math_private.h"
  21 #if __UCLIBC_HAS_FENV__
  22 #include <fenv.h>
  23 #endif
  24
  25 /* wrapper log2f(x) */
  26 float
  27 log2f (float x)
  28 {
  29 #if __UCLIBC_HAS_FENV__
  30   if (__builtin_expect (islessequal (x, 0.0f), 0) && _LIB_VERSION != _IEEE_)
  31     {
  32       if (x == 0.0)
  33         {
  34           feraiseexcept (FE_DIVBYZERO);
  35           return __kernel_standard_f (x, x, 148); /* log2(0) */
  36         }
  37       else
  38         {
  39           feraiseexcept (FE_INVALID);
  40           return __kernel_standard_f (x, x, 149); /* log2(x<0) */
  41         }
  42     }
  43 #endif
  44   return (float) __ieee754_log2 ((double) x);
  45 }