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/*
Copyright (C) 2016 Pascal Molin
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 "nmod.h"
#include "dlog.h"
ulong
dlog_mod2e_1mod4(ulong b1, ulong e, ulong inv5, nmod_t pe)
{
slong f;
ulong pf1, pf, x, xf;
pf1 = 1;
pf = 4;
x = 0;
for (f = 2; f < e; f++)
{
if (b1 % pf != 1)
{
flint_throw(FLINT_ERROR, "ERROR dlog_mod2e: %wu %% %wu != 1 mod %wu\n\n", b1, pf, pe.n);
}
xf = (b1 - 1) / pf;
xf = (f == 2) ? xf % 4 : (xf % 2) * (pf1 / 2);
b1 = nmod_mul(b1, nmod_pow_ui(inv5, xf, pe), pe);
x += xf;
pf1 = pf;
pf *= 2;
}
return x;
}
ulong
dlog_mod2e(const dlog_modpe_t t, ulong b1)
{
if (t->e == 2)
return (b1 % 4) == 3;
else
return dlog_mod2e_1mod4(b1, t->e, t->inva, t->pe);
}