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/*
Copyright (C) 2012 William Hart
Copyright (C) 2025 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 "mpn_extras.h"
void flint_mpn_preinvn(mp_ptr dinv, mp_srcptr d, mp_size_t n)
{
mp_ptr q, r, d1, tmp;
TMP_INIT;
TMP_START;
tmp = TMP_ALLOC((n + (2 * n + 1) + (n + 2)) * sizeof(mp_limb_t));
d1 = tmp;
r = d1 + n;
q = r + (2 * n + 1);
if (mpn_add_1(d1, d, n, 1)) /* check for d + 1 == 0 */
{
flint_mpn_zero(dinv, n);
}
else
{
flint_mpn_zero(r, 2 * n);
r[2*n] = 1;
mpn_tdiv_qr(q, r, 0, r, 2 * n + 1, d1, n);
flint_mpn_copyi(dinv, q, n);
}
TMP_END;
}