1/* Compute radix independent exponent.
2 Copyright (C) 2011-2021 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 <https://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
26double
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
48libm_alias_double (__logb, logb)
49#endif
50