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/* Return arc sine of X, divided by pi.
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-narrow-eval.h>
#include <math_private.h>
#include <math-underflow.h>
FLOAT
M_DECL_FUNC (__asinpi) (FLOAT x)
{
if (__glibc_unlikely (!islessequal (M_FABS (x), M_LIT (1.0))))
{
if (!isnan (x))
__set_errno (EDOM);
return (x - x) / (x - x);
}
FLOAT ret = math_narrow_eval (M_SUF (__ieee754_asin) (x) / M_MLIT (M_PI));
math_check_force_underflow (ret);
if (x != 0 && ret == 0)
__set_errno (ERANGE);
/* Ensure that rounding away from zero for both asin and the
division cannot yield a return value from asinpi with absolute
value greater than 0.5. */
return (isgreater (M_FABS (ret), M_LIT (0.5))
? M_COPYSIGN (M_LIT (0.5), ret)
: ret);
}
declare_mgen_alias (__asinpi, asinpi);
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