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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_modular.h"
void
acb_modular_fill_addseq(slong * tab, slong len)
{
slong i, j;
for (i = 2; i < len; i++)
{
if (tab[i] == -1)
{
/* prefer doubling (squaring) */
if ((i % 2) == 0 && tab[i / 2] != 0)
{
tab[i] = i / 2;
}
else
{
/* check if it can be written as a sum */
/* prefer unbalanced, because one power will have low precision */
#if 1
for (j = 1; 2 * j <= i; j++)
#else
for (j = i / 2; j >= 1; j--)
#endif
{
if (tab[j] != 0 && tab[i-j] != 0)
{
tab[i] = j;
break;
}
}
/* extend and start over */
if (tab[i] == -1)
{
tab[i] = i / 2;
if (tab[i / 2] == 0)
tab[i / 2] = -1;
if (tab[i - i / 2] == 0)
tab[i - i / 2] = -1;
i = 1;
}
}
}
}
/* prefer squaring (extra entries may have been inserted) */
for (i = 2; i < len; i += 2)
{
if (tab[i] != 0 && tab[i] != i / 2)
{
if (tab[i / 2] != 0)
tab[i] = i / 2;
}
}
}