sysdeps/ieee754/dbl-64/s_logb.c

   1 /* Compute radix independent exponent.
   2    Copyright (C) 2011-2019 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 #include <libm-alias-double.h>
  24 #include <fix-int-fp-convert-zero.h>
  25
  26 double
  27 __logb (double x)
  28 {
  29   int64_t ix, ex;
  30
  31   EXTRACT_WORDS64 (ix, x);
  32   ix &= UINT64_C(0x7fffffffffffffff);
  33   if (ix == 0)
  34     return -1.0 / fabs (x);
  35   ex = ix >> 52;
  36   if (ex == 0x7ff)
  37     return x * x;
  38   if (__glibc_unlikely (ex == 0))
  39     {
  40       int m = __builtin_clzll (ix);
  41       ex -= m - 12;
  42     }
  43   if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
  44     return 0.0;
  45   return (double) (ex - 1023);
  46 }
  47 #ifndef __logb
  48 libm_alias_double (__logb, logb)
  49 #endif