1/* Compute radix independent exponent.
2 Copyright (C) 2011-2023 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
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 <https://www.gnu.org/licenses/>. */
18
19#include <math.h>
20
21#include <math_private.h>
22#include <libm-alias-double.h>
23#include <fix-int-fp-convert-zero.h>
24#include <math-use-builtins.h>
25
26double
27__logb (double x)
28{
29#if USE_LOGB_BUILTIN
30 return __builtin_logb (x);
31#else
32 int64_t ix, ex;
33
34 EXTRACT_WORDS64 (ix, x);
35 ix &= UINT64_C(0x7fffffffffffffff);
36 if (ix == 0)
37 return -1.0 / fabs (x);
38 ex = ix >> 52;
39 if (ex == 0x7ff)
40 return x * x;
41 if (__glibc_unlikely (ex == 0))
42 {
43 int m = __builtin_clzll (ix);
44 ex -= m - 12;
45 }
46 if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
47 return 0.0;
48 return (double) (ex - 1023);
49#endif /* !USE_LOGB_BUILTIN */
50}
51#ifndef __logb
52libm_alias_double (__logb, logb)
53#endif
54