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/* Compute radix independent exponent.
Copyright (C) 2011-2018 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@gmail.com>, 2011.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <math.h>
#include <math_private.h>
#include <libm-alias-double.h>
double
__logb (double x)
{
int64_t ix, ex;
EXTRACT_WORDS64 (ix, x);
ix &= UINT64_C(0x7fffffffffffffff);
if (ix == 0)
return -1.0 / fabs (x);
ex = ix >> 52;
if (ex == 0x7ff)
return x * x;
if (__glibc_unlikely (ex == 0))
{
int m = __builtin_clzll (ix);
ex -= m - 12;
}
return (double) (ex - 1023);
}
#ifndef __logb
libm_alias_double (__logb, logb)
#endif
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