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/*
Copyright (C) 2016 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include <math.h>
#include "mag.h"
#include "mag/impl.h"
void
mag_expinv(mag_t res, const mag_t x)
{
if (mag_is_zero(x))
{
mag_one(res);
}
else if (mag_is_inf(x))
{
mag_zero(res);
}
else if (mag_cmp_2exp_si(x, 24) >= 0)
{
mag_exp_huge_lower(res, x);
mag_inv(res, res);
}
else if (COEFF_IS_MPZ(MAG_EXP(x)))
{
mag_one(res);
}
else
{
slong e = MAG_EXP(x);
if (e <= -MAG_BITS)
mag_one(res);
else
_mag_exp_d(res, -ldexp(MAG_MAN(x), e - MAG_BITS), 1);
}
}
void
mag_expinv_lower(mag_t res, const mag_t x)
{
if (mag_is_zero(x))
{
mag_one(res);
}
else if (mag_is_inf(x))
{
mag_zero(res);
}
else if (mag_cmp_2exp_si(x, 24) >= 0)
{
mag_exp_huge(res, x);
mag_inv_lower(res, res);
}
else if (COEFF_IS_MPZ(MAG_EXP(x)))
{
/* 1 - eps */
MAG_MAN(res) = (1 << MAG_BITS) - 1;
fmpz_zero(MAG_EXPREF(res));
}
else
{
slong e = MAG_EXP(x);
if (e < -MAG_BITS)
{
/* 1 - eps */
MAG_MAN(res) = (1 << MAG_BITS) - 1;
fmpz_zero(MAG_EXPREF(res));
}
else
_mag_exp_d(res, -ldexp(MAG_MAN(x), e - MAG_BITS), 0);
}
}