mirror of
https://github.com/vale981/arb
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42 lines
1 KiB
C
42 lines
1 KiB
C
/*
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Copyright (C) 2016 Pascal Molin
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This file is part of Arb.
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Arb is free software: you can redistribute it and/or modify it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include <stdlib.h>
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#include "dlog.h"
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int
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apow_cmp(const apow_t * x, const apow_t * y)
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{
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return (x->ak < y->ak) ? -1 : (x->ak > y->ak);
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}
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ulong
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dlog_bsgs_init(dlog_bsgs_t t, ulong a, ulong mod, ulong n, ulong m)
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{
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ulong k, ak;
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if (m >= n) m = n;
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t->table = (apow_t *)flint_malloc(m * sizeof(apow_t));
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nmod_init(&t->mod, mod);
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t->m = m;
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t->g = n / m + 1;
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for (k = 0, ak = 1; k < m; k++)
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{
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t->table[k].k = k;
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t->table[k].ak = ak;
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ak = nmod_mul(ak, a, t->mod);
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}
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t->am = nmod_inv(ak, t->mod);
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qsort(t->table, m, sizeof(apow_t), (int(*)(const void*,const void*))apow_cmp);
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return t->g;
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}
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