arb/dlog/crt.c

/*=============================================================================

    This file is part of ARB.

    ARB is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    ARB is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with ARB; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA

=============================================================================*/
/******************************************************************************

    Copyright (C) 2016 Pascal Molin

******************************************************************************/

#include "dlog.h"

ulong
dlog_crt(const dlog_crt_t t, ulong b)
{
    int k;
    ulong r = 0;
    for (k = 0; k < t->num; k++)
    {
        ulong bk, rk;
        bk = nmod_pow_ui(b, t->expo[k], t->mod);
        rk = dlog_precomp(t->pre[k], bk);
#if 0
        flint_printf("##[crt-%d]: log(%wu)=log(%wu^%wu) = %wu [size %wu mod %wu]\n",
                k, bk, b, t->expo[k], rk, t->n/t->expo[k], t->mod);
#endif
        r = nmod_add(r, nmod_mul(t->crt_coeffs[k], rk, t->n), t->n);
    }
    return r;
}