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/*
Copyright (C) 2015 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 "acb.h"
void
acb_acos(acb_t res, const acb_t z, slong prec)
{
if (acb_is_one(z))
{
acb_zero(res);
}
else
{
acb_t t;
acb_init(t);
acb_one(t);
if (arb_is_zero(acb_imagref(z))
&& arb_gt(acb_realref(z), acb_realref(t)))
{
/* pure imaginary on (1,inf) */
acb_asin(res, z, prec);
acb_neg(res, res);
arb_zero(acb_realref(res));
}
else
{
acb_asin(res, z, prec);
acb_const_pi(t, prec);
acb_mul_2exp_si(t, t, -1);
acb_sub(res, t, res, prec);
}
acb_clear(t);
}
}