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/* Return base-2 logarithm of 1 + X.
Copyright (C) 2024-2025 Free Software Foundation, Inc.
This file is part of the GNU C Library.
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
<https://www.gnu.org/licenses/>. */
#include <errno.h>
#include <math.h>
#include <math-underflow.h>
FLOAT
M_DECL_FUNC (__log2p1) (FLOAT x)
{
if (__glibc_unlikely (islessequal (x, M_LIT (-1.0))))
{
if (x == -1)
__set_errno (ERANGE);
else
__set_errno (EDOM);
}
if (isless (M_FABS (x), M_EPSILON / 4))
{
/* Avoid spurious underflows when log1p underflows but log2p1
should not. */
FLOAT ret = M_MLIT (M_LOG2E) * x;
math_check_force_underflow (ret);
return ret;
}
return M_MLIT (M_LOG2E) * M_SUF (__log1p) (x);
}
declare_mgen_alias (__log2p1, log2p1);
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