1/* Compute radix independent exponent.
2 Copyright (C) 2011-2016 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
25double
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 (__glibc_unlikely (ex == 0))
38 {
39 int m = __builtin_clzll (ix);
40 ex -= m - 12;
41 }
42 return (double) (ex - 1023);
43}
44weak_alias (__logb, logb)
45#ifdef NO_LONG_DOUBLE
46strong_alias (__logb, __logbl)
47weak_alias (__logb, logbl)
48#endif
49