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/*
Copyright (C) 2009, 2013, 2016 William Hart
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 "ulong_extras.h"
ulong
n_powmod2_preinv(ulong a, slong exp, ulong n, ulong ninv)
{
ulong norm;
FLINT_ASSERT(n != 0);
if (a >= n)
a = n_mod2_preinv(a, n, ninv);
if (exp < 0)
{
ulong g = n_gcdinv(&a, a, n);
if (g != 1)
flint_throw(FLINT_IMPINV, "Cannot invert modulo %wd*%wd\n", g,
n / g);
exp = -(ulong) exp;
}
norm = flint_clz(n);
return n_powmod_ui_preinv(a << norm, exp, n << norm, ninv, norm) >> norm;
}