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/* mpfr_pow_ui-- compute the power of a floating-point
by a machine integer
Copyright 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
This file is part of the MPFR Library.
The 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 2.1 of the License, or (at your
option) any later version.
The 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 MPFR Library; see the file COPYING.LIB. If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */
#include "gmp.h"
#include "mpfr.h"
#include "mpfr-impl.h"
/* sets x to y^n, and return 0 if exact, non-zero otherwise */
int
mpfr_pow_ui (mpfr_ptr x, mpfr_srcptr y, unsigned long int n, mp_rnd_t rnd)
{
long int i, err;
unsigned long m;
mpfr_t res;
mp_prec_t prec;
int inexact;
mp_rnd_t rnd1;
if (MPFR_IS_NAN(y))
{
MPFR_SET_NAN(x);
MPFR_RET_NAN;
}
MPFR_CLEAR_NAN(x);
if (n == 0) /* x^0 = 1 for any x */
{
/* The return mpfr_set_ui is important as 1 isn't necessarily
in the exponent range. */
return mpfr_set_ui (x, 1, rnd);
}
if (MPFR_IS_INF(y))
{
/* Inf^n = Inf, (-Inf)^n = Inf for n even, -Inf for n odd */
if ((MPFR_SIGN(y) < 0) && (n % 2 == 1))
MPFR_SET_NEG(x);
else
MPFR_SET_POS(x);
MPFR_SET_INF(x);
MPFR_RET(0);
}
MPFR_CLEAR_INF(x);
mpfr_init (res);
prec = MPFR_PREC(x);
rnd1 = (MPFR_SIGN(y) > 0) ? GMP_RNDU : GMP_RNDD; /* away */
do
{
prec += 3;
for (m=n, i=0; m; i++, m>>=1, prec++);
mpfr_set_prec (res, prec);
inexact = mpfr_set (res, y, rnd1);
err = 1;
/* now 2^(i-1) <= n < 2^i */
for (i-=2; i>=0; i--)
{
if (mpfr_mul (res, res, res, GMP_RNDU))
inexact = 1;
err++;
if (n & (1 << i))
if (mpfr_mul (res, res, y, rnd1))
inexact = 1;
}
err = prec - err;
if (err < 0)
err = 0;
}
while (inexact && (mpfr_can_round (res, err,
(MPFR_SIGN(res) > 0) ? GMP_RNDU : GMP_RNDD, rnd, MPFR_PREC(x)) == 0));
if (mpfr_set (x, res, rnd))
inexact = 1;
mpfr_clear (res);
return inexact;
}
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