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/* Return exp2(X) - 1.
Copyright (C) 2024 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 <fenv.h>
#include <math.h>
#include <math_private.h>
#include <math-underflow.h>
FLOAT
M_DECL_FUNC (__exp2m1) (FLOAT x)
{
if (isgreaterequal (x, M_LIT (-1.0)) && islessequal (x, M_LIT (1.0)))
{
FLOAT ret = M_SUF (__expm1) (M_MLIT (M_LN2) * x);
math_check_force_underflow (ret);
if (x != 0 && ret == 0)
__set_errno (ERANGE);
return ret;
}
else if (isgreater (x, M_MANT_DIG + M_LIT (2.0)))
{
#if defined FE_DOWNWARD || defined FE_TOWARDZERO
/* exp2m1 (MAX_EXP) should not overflow in these two rounding
modes, but exp2 does overflow. */
if (x == M_MAX_EXP)
{
int rnd_mode = fegetround ();
if (0
# ifdef FE_DOWNWARD
|| rnd_mode == FE_DOWNWARD
# endif
# ifdef FE_TOWARDZERO
|| rnd_mode == FE_TOWARDZERO
# endif
)
return M_MAX;
}
#endif
FLOAT ret = M_SUF (__ieee754_exp2) (x);
if (!isfinite (ret) && isfinite (x))
__set_errno (ERANGE);
return ret;
}
else if (isless (x, -M_MANT_DIG - M_LIT (2.0)))
return M_LIT (-1.0);
else
return M_SUF (__ieee754_exp2) (x) - M_LIT (1.0);
}
declare_mgen_alias (__exp2m1, exp2m1);
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