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/* mpfr_powr -- powr(x,y) = exp(y*log(x))
Copyright 2021 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR 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 3 of the License, or (at your
option) any later version.
The GNU MPFR 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 MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include "mpfr-impl.h"
int
mpfr_powr (mpfr_ptr z, mpfr_srcptr x, mpfr_srcptr y, mpfr_rnd_t rnd_mode)
{
/* powr(x,y) is NaN for x=NaN or x < 0 (a)
powr(+/-0,+/-0) is NaN whereas pow(x,+/-0) = 1 if x is not NaN (b)
powr(+Inf,+/-0) is NaN whereas pow(x,+/-0) = 1 if x is not NaN (b)
We can use MPFR_IS_SINGULAR since we already excluded x=NaN and x=-Inf.
powr(1,+/-Inf) = NaN whereas pow(1,+/-Inf) = 1 (c) */
if (MPFR_IS_NAN (x) || MPFR_IS_STRICTNEG(x) || /* case (a) */
(MPFR_IS_SINGULAR(x) && MPFR_IS_ZERO(y)) || /* case (b) */
(mpfr_cmp_ui (x, 1) == 0 && MPFR_IS_INF(y))) /* case (c) */
{
MPFR_SET_NAN (z);
MPFR_RET_NAN;
}
/* for finite y < 0, powr(-0,y) is +Inf, whereas pow(-0,y) is -Inf for y an
odd negativeinteger, and +Inf otherwise */
if (MPFR_IS_ZERO(x) && MPFR_SIGN(x) < 0 && !MPFR_IS_SINGULAR (y)
&& MPFR_IS_NEG(y))
{
MPFR_SET_INF (z);
MPFR_SET_POS (z);
MPFR_SET_DIVBY0 ();
MPFR_RET (0);
}
/* for y > 0, powr(-0,y) is +0, whereas pow gives -0 for y an odd integer */
if (MPFR_IS_ZERO(x) && MPFR_SIGN(x) < 0 && !MPFR_IS_SINGULAR (y)
&& MPFR_IS_POS(y))
{
MPFR_SET_ZERO (z);
MPFR_SET_POS (z);
MPFR_RET (0);
}
/* otherwise powr coincides with pow */
return mpfr_pow (z, x, y, rnd_mode);
}
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