mirror of
https://github.com/vale981/arb
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82 lines
2.1 KiB
C
82 lines
2.1 KiB
C
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/*=============================================================================
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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
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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ARB is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with ARB; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2016 Pascal Molin
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******************************************************************************/
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#include "dlog.h"
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void
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dlog_power_init(dlog_power_t t, ulong a, ulong mod, ulong p, ulong e, ulong num)
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{
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int k;
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t->mod = mod;
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t->p = p;
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t->e = e;
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t->apk = flint_malloc(e * sizeof(ulong));
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t->pre = flint_malloc(sizeof(dlog_precomp_struct));
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t->apk[0] = n_invmod(a, mod);
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for (k = 1; k < e; k++)
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t->apk[k] = n_powmod(t->apk[k-1], p, mod);
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dlog_precomp_p_init(t->pre, n_invmod(t->apk[e-1], mod), mod, p, num);
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}
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void
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dlog_power_clear(dlog_power_t t)
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{
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flint_free(t->apk);
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dlog_precomp_clear(t->pre);
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flint_free(t->pre);
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}
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/* 3^30*2+1, 2^30*3+1 are primes */
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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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#ifdef C99
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ulong pk[t->e];
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#else
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ulong pk[30];
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#endif
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ulong x;
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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 = n_powmod(b, pk[t->e-1-k], t->mod);
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xk = dlog_precomp(t->pre, bk);
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b = b * n_powmod(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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