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/* Return the Yth root of X for integer Y.
Copyright (C) 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 <limits.h>
#include <math.h>
#include <math-narrow-eval.h>
#include <math_private.h>
FLOAT
M_DECL_FUNC (__rootn) (FLOAT x, long long int y)
{
if (y == 0)
{
/* This is a domain error even if X is a NaN. */
__set_errno (EDOM);
return M_LIT (0.0) / M_LIT (0.0);
}
if (isnan (x))
return x + x;
if (x < 0 && (y & 1) == 0)
{
__set_errno (EDOM);
return (x - x) / (x - x);
}
if (isinf (x))
/* If X is negative, then Y is odd. */
return y > 0 ? x : M_LIT (1.0) / x;
if (x == M_LIT (0.0))
{
if (y > 0)
return (y & 1) == 0 ? M_LIT (0.0) : x;
else
{
__set_errno (ERANGE);
return M_LIT (1.0) / ((y & 1) == 0 ? M_LIT (0.0) : x);
}
}
if (y == 1)
return x;
if (y == -1)
{
/* Overflow is possible in this case (and underflow, though not
underflow to zero). */
FLOAT ret = math_narrow_eval (M_LIT (1.0) / x);
if (isinf (ret))
__set_errno (ERANGE);
return ret;
}
/* Now X is finite and no overflow or underflow (or results even
close to overflowing or underflowing) is possible. If X is
negative, then Y is odd; the result should have the sign of X. */
if (y >= 4 * M_MAX_EXP || y <= -4 * M_MAX_EXP)
/* No extra precision is needed in computing the exponent; it is
OK if Y cannot be exactly represented in type FLOAT. */
return M_COPYSIGN (M_SUF (__ieee754_pow) (M_FABS (x), M_LIT (1.0) / y), x);
/* Compute 1 / Y with extra precision. Y can be exactly represented
in type FLOAT. */
FLOAT qhi, qlo;
qhi = math_narrow_eval (M_LIT (1.0) / y);
qlo = M_SUF (fma) (-qhi, y, 1.0) / y;
return M_COPYSIGN (M_SUF (__ieee754_pow) (M_FABS (x), qhi)
* M_SUF (__ieee754_pow) (M_FABS (x), qlo), x);
}
declare_mgen_alias (__rootn, rootn);
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