1 /* Compute radix independent exponent.
2    Copyright (C) 2011-2022 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 
25 double
__logb(double x)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   if (FIX_INT_FP_CONVERT_ZERO && ex == 1023)
43     return 0.0;
44   return (double) (ex - 1023);
45 }
46 #ifndef __logb
47 libm_alias_double (__logb, logb)
48 #endif
49