sysdeps/ieee754/dbl-64/wordsize-64/s_logb.c

   1 /* Compute radix independent exponent.
   2    Copyright (C) 2011, 2012 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <math.h>
  21
  22 #include <math_private.h>
  23
  24
  25 double
  26 __logb (double x)
  27 {
  28   int64_t ix, ex;
  29
  30   EXTRACT_WORDS64 (ix, x);
  31   ix &= UINT64_C(0x7fffffffffffffff);
  32   if (ix == 0)
  33     return -1.0 / fabs (x);
  34   ex = ix >> 52;
  35   if (ex == 0x7ff)
  36     return x * x;
  37   if (__builtin_expect (ex == 0, 0))
  38     {
  39       int m = __builtin_clzll (ix);
  40       ex -= m - 12;
  41     }
  42   return (double) (ex - 1023);
  43 }
  44 weak_alias (__logb, logb)
  45 #ifdef NO_LONG_DOUBLE
  46 strong_alias (__logb, __logbl)
  47 weak_alias (__logb, logbl)
  48 #endif