pqc/external/flint-2.4.3/fmpz_poly/hensel_continue_lift.c
2014-05-24 23:16:06 +02:00

115 lines
3.2 KiB
C

/*=============================================================================
This file is part of FLINT.
FLINT 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.
FLINT 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 FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2011 Andy Novocin
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include "fmpz_poly.h"
slong _fmpz_poly_hensel_continue_lift(fmpz_poly_factor_t lifted_fac,
slong *link, fmpz_poly_t *v, fmpz_poly_t *w, const fmpz_poly_t f,
slong prev, slong curr, slong N, const fmpz_t p)
{
const slong r = lifted_fac->num;
slong i, new_prev;
fmpz_t P;
fmpz_poly_t monic_f;
fmpz_init(P);
fmpz_pow_ui(P, p, N);
fmpz_poly_init(monic_f);
if (fmpz_is_one(fmpz_poly_lead(f)))
{
fmpz_poly_set(monic_f, f);
}
else if (fmpz_cmp_si(fmpz_poly_lead(f), -1) == 0)
{
fmpz_poly_neg(monic_f, f);
}
else
{
fmpz_t t;
fmpz_init(t);
fmpz_mod(t, fmpz_poly_lead(f), P);
if (fmpz_invmod(t, t, P) == 0)
{
flint_printf("Exception (fmpz_poly_continue_hensel_lift).\n");
abort();
}
fmpz_poly_scalar_mul_fmpz(monic_f, f, t);
fmpz_poly_scalar_mod_fmpz(monic_f, monic_f, P);
fmpz_clear(t);
}
{
slong *e, n = 3 + FLINT_FLOG2(N - prev);
e = flint_malloc(n * sizeof(slong));
for (e[i = 0] = N; e[i] > curr; i++)
e[i + 1] = (e[i] + 1) / 2;
e[i] = curr;
e[i+1] = prev;
if (prev < curr)
fmpz_poly_hensel_lift_tree(link, v, w, monic_f, r, p, e[i+1], e[i], -1);
for (i--; i > 0; i--)
fmpz_poly_hensel_lift_tree(link, v, w, monic_f, r, p, e[i+1], e[i], 1);
fmpz_poly_hensel_lift_tree(link, v, w, monic_f, r, p, e[i+1], e[i], 0);
new_prev = e[i+1];
flint_free(e);
}
/*
Now everything is lifted to p^N, we just need to
insert the factors into their correct places in lifted_fac.
*/
fmpz_poly_factor_fit_length(lifted_fac, r);
for(i = 0; i < 2*r - 2; i++)
{
if (link[i] < 0)
{
fmpz_poly_scalar_smod_fmpz(lifted_fac->p + (- link[i] - 1), v[i], P);
lifted_fac->exp[- link[i] - 1] = WORD(1);
}
}
lifted_fac->num = r;
fmpz_clear(P);
fmpz_poly_clear(monic_f);
return new_prev;
}