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/* Return X^Y 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 <fenv_private.h>
#include <limits.h>
#include <math.h>
#include <math-barriers.h>
#include <math-narrow-eval.h>
#include <math_private.h>
#include <stdlib.h>
FLOAT
M_DECL_FUNC (__pown) (FLOAT x, long long int y)
{
FLOAT ret;
#if M_MANT_DIG >= LLONG_WIDTH - 1
ret = M_SUF (__ieee754_pow) (x, y);
#else
if ((y <= 1LL << M_MANT_DIG
&& y >= -(1LL << M_MANT_DIG))
|| y == LLONG_MIN)
ret = M_SUF (__ieee754_pow) (x, y);
else
{
{
/* To avoid problems with overflow and underflow from
intermediate computations occurring in the wrong directed
rounding mode (when X is negative and Y is odd), do these
computations in round-to-nearest mode and correct
overflowing and underflowing results afterwards. */
M_SET_RESTORE_ROUND (FE_TONEAREST);
ret = M_LIT (1.0);
while (y != 0)
{
long long int absy = llabs (y);
int bits = LLONG_WIDTH - __builtin_clzll (absy);
if (bits <= M_MANT_DIG)
{
ret *= M_SUF (__ieee754_pow) (x, y);
y = 0;
}
else
{
long long int absy_high
= absy & (((1ULL << M_MANT_DIG) - 1) << (bits - M_MANT_DIG));
long long int absy_low = absy - absy_high;
long long int y_high = y < 0 ? -absy_high : absy_high;
ret *= M_SUF (__ieee754_pow) (x, y_high);
y = y < 0 ? -absy_low : absy_low;
}
}
ret = math_narrow_eval (ret);
math_force_eval (ret);
}
if (isfinite (x) && x != M_LIT (0.0))
{
if (isinf (ret))
ret = math_narrow_eval (M_COPYSIGN (M_MAX, ret) * M_MAX);
else if (ret == M_LIT (0.0))
ret = math_narrow_eval (M_COPYSIGN (M_MIN, ret) * M_MIN);
}
}
#endif
if (!isfinite (ret))
{
if (isfinite (x))
__set_errno (ERANGE);
}
else if (ret == 0
&& isfinite (x)
&& x != 0)
__set_errno (ERANGE);
return ret;
}
declare_mgen_alias (__pown, pown);
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