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https://github.com/vale981/arb
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37 lines
881 B
C
37 lines
881 B
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 "dlog.h"
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ulong
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dlog_power(const dlog_power_t t, ulong b)
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{
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int k;
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ulong x, pk[30]; /* 3^30*2+1, 2^30*3+1 are primes */
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pk[0] = 1;
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for (k = 1; k < t->e; k++)
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pk[k] = pk[k-1] * t->p;
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x = 0;
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for(k = 0; k < t->e; k++)
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{
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ulong bk, xk;
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bk = nmod_pow_ui(b, pk[t->e-1-k], t->mod);
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xk = dlog_precomp(t->pre, bk);
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b = nmod_mul(b, nmod_pow_ui(t->apk[k], xk, t->mod), t->mod);
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x += xk * pk[k]; /* cannot overflow */
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}
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return x;
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}
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