pqc/external/flint-2.4.3/nmod_poly/divrem_divconquer.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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) 2008, 2009, 2011 William Hart
Copyright (C) 2011 Sebastian Pancratz
Copyright (C) 2012 Fredrik Johansson
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
static
void __nmod_poly_divrem_divconquer(mp_ptr Q, mp_ptr R,
mp_srcptr A, slong lenA,
mp_srcptr B, slong lenB, nmod_t mod)
{
if (lenA < 2 * lenB - 1)
{
/*
Convert unbalanced division into a 2 n1 - 1 by n1 division
*/
const slong n1 = lenA - lenB + 1;
const slong n2 = lenB - n1;
mp_srcptr p1 = A + n2;
mp_srcptr d1 = B + n2;
mp_srcptr d2 = B;
mp_ptr V = _nmod_vec_init((n1 - 1) + lenB - 1 + NMOD_DIVREM_DC_ITCH(n1, mod));
mp_ptr W = V + NMOD_DIVREM_DC_ITCH(n1, mod);
mp_ptr d1q1 = R + n2;
mp_ptr d2q1 = W;
_nmod_poly_divrem_divconquer_recursive(Q, d1q1, W, V, p1, d1, n1, mod);
/*
Compute d2q1 = Q d2, of length lenB - 1
*/
if (n1 >= n2)
_nmod_poly_mul(d2q1, Q, n1, d2, n2, mod);
else
_nmod_poly_mul(d2q1, d2, n2, Q, n1, mod);
/*
Compute BQ = d1q1 * x^n1 + d2q1, of length lenB - 1;
then compute R = A - BQ
*/
flint_mpn_copyi(R, d2q1, n2);
_nmod_vec_add(R + n2, R + n2, d2q1 + n2, n1 - 1, mod);
_nmod_vec_sub(R, A, R, lenB - 1, mod);
_nmod_vec_clear(V);
}
else /* lenA = 2 * lenB - 1 */
{
mp_ptr V = _nmod_vec_init(lenB - 1 + NMOD_DIVREM_DC_ITCH(lenB, mod));
mp_ptr W = V + NMOD_DIVREM_DC_ITCH(lenB, mod);
_nmod_poly_divrem_divconquer_recursive(Q, R, W, V, A, B, lenB, mod);
_nmod_vec_sub(R, A, R, lenB - 1, mod);
_nmod_vec_clear(V);
}
}
void _nmod_poly_divrem_divconquer(mp_ptr Q, mp_ptr R,
mp_srcptr A, slong lenA,
mp_srcptr B, slong lenB, nmod_t mod)
{
if (lenA <= 2 * lenB - 1)
{
__nmod_poly_divrem_divconquer(Q, R, A, lenA, B, lenB, mod);
}
else /* lenA > 2 * lenB - 1 */
{
slong shift, n = 2 * lenB - 1;
mp_ptr S, QB, W, V, T;
S = _nmod_vec_init(lenA + 2 * (lenB - 1) + n + NMOD_DIVREM_DC_ITCH(lenB, mod));
QB = S + lenA;
W = QB + (lenB - 1);
T = W + (lenB - 1);
V = T + n;
_nmod_vec_set(S, A, lenA);
while (lenA >= n)
{
shift = lenA - n;
_nmod_poly_divrem_divconquer_recursive(Q + shift, QB, W, V, S + shift, B, lenB, mod);
_nmod_vec_sub(S + shift, S + shift, QB, lenB - 1, mod);
lenA -= lenB;
}
if (lenA >= lenB)
{
__nmod_poly_divrem_divconquer(Q, T, S, lenA, B, lenB, mod);
_nmod_vec_set(S, T, lenA);
}
_nmod_vec_set(R, S, lenB - 1);
_nmod_vec_clear(S);
}
}
void nmod_poly_divrem_divconquer(nmod_poly_t Q, nmod_poly_t R,
const nmod_poly_t A, const nmod_poly_t B)
{
nmod_poly_t tQ, tR;
mp_ptr q, r;
slong lenA, lenB;
lenA = A->length;
lenB = B->length;
if (lenB == 0)
{
flint_printf("Exception (nmod_poly_divrem_divconquer). Division by zero.\n");
abort();
}
if (lenA < lenB)
{
nmod_poly_set(R, A);
nmod_poly_zero(Q);
return;
}
if (Q == A || Q == B)
{
nmod_poly_init2(tQ, A->mod.n, lenA - lenB + 1);
q = tQ->coeffs;
}
else
{
nmod_poly_fit_length(Q, lenA - lenB + 1);
q = Q->coeffs;
}
if (R == A || R == B)
{
nmod_poly_init2(tR, A->mod.n, lenB - 1);
r = tR->coeffs;
}
else
{
nmod_poly_fit_length(R, lenB - 1);
r = R->coeffs;
}
_nmod_poly_divrem_divconquer(q, r, A->coeffs, lenA,
B->coeffs, lenB, A->mod);
if (Q == A || Q == B)
{
nmod_poly_swap(tQ, Q);
nmod_poly_clear(tQ);
}
if (R == A || R == B)
{
nmod_poly_swap(tR, R);
nmod_poly_clear(tR);
}
Q->length = lenA - lenB + 1;
R->length = lenB - 1;
_nmod_poly_normalise(R);
}