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/*
Copyright (C) 2012 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 "mpn_extras.h"
mp_limb_t flint_mpn_preinv1(mp_limb_t d1, mp_limb_t d2)
{
mp_limb_t q, r[2], p[2], cy;
if (d2 + 1 == 0 && d1 + 1 == 0)
return 0;
if (d1 + 1 == 0)
q = ~d1, r[1] = ~d2;
else
udiv_qrnnd(q, r[1], ~d1, ~d2, d1 + 1);
if (d2 + 1 == 0)
return q;
r[0] = 0;
umul_ppmm(p[1], p[0], q, ~d2);
cy = mpn_add_n(r, r, p, 2);
p[0] = d2 + 1, p[1] = d1 + (d2 + 1 == 0);
while (cy || mpn_cmp(r, p, 2) >= 0)
{
q++;
cy -= mpn_sub_n(r, r, p, 2);
}
return q;
}