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/*=============================================================================
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) 2012 Fredrik Johansson
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "nmod_vec.h"
#include "nmod_poly.h"
static void
__nmod_poly_div_divconquer(mp_ptr Q, 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_ptr V = _nmod_vec_init(n1 - 1 + NMOD_DIVREM_DC_ITCH(n1, mod));
mp_ptr W = V + NMOD_DIVREM_DC_ITCH(n1, mod);
_nmod_poly_div_divconquer_recursive(Q, W, V, p1, d1, n1, 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_div_divconquer_recursive(Q, W, V, A, B, lenB, mod);
_nmod_vec_clear(V);
}
}
/* needed due to partial overlap */
static void
_nmod_vec_sub_dec(mp_ptr a, mp_srcptr b, mp_srcptr c, slong n, nmod_t mod)
{
slong i;
for (i = n - 1; i >= 0; i--)
a[i] = n_submod(b[i], c[i], mod.n);
}
void
_nmod_poly_div_divconquer(mp_ptr Q, mp_srcptr A, slong lenA,
mp_srcptr B, slong lenB, nmod_t mod)
{
if (lenA <= 2 * lenB - 1)
{
__nmod_poly_div_divconquer(Q, A, lenA, B, lenB, mod);
}
else /* lenA > 2 * lenB - 1 */
{
mp_ptr S, T, V, R;
slong shift, next, n = 2 * lenB - 1;
S = _nmod_vec_init(2 * n + (lenB - 1) + NMOD_DIVREM_DC_ITCH(lenB, mod));
T = S + n;
R = T + n;
V = R + (lenB - 1);
shift = lenA - n;
_nmod_vec_set(S, A + shift, n);
while (lenA >= n)
{
shift = lenA - n;
_nmod_poly_divrem_divconquer_recursive(Q + shift, T, R, V, S, B, lenB, mod);
next = FLINT_MIN(lenB, shift);
_nmod_vec_sub_dec(S + next, S, T, lenB - 1, mod);
_nmod_vec_set(S, A + shift - next, next);
lenA -= lenB;
}
if (lenA >= lenB)
__nmod_poly_div_divconquer(Q, S, lenA, B, lenB, mod);
_nmod_vec_clear(S);
}
}
void
nmod_poly_div_divconquer(nmod_poly_t Q,
const nmod_poly_t A, const nmod_poly_t B)
{
nmod_poly_t tQ;
mp_ptr q;
slong Alen, Blen;
Blen = B->length;
if (Blen == 0)
{
flint_printf("Exception (nmod_poly_div_divconquer). Division by zero.\n");
abort();
}
Alen = A->length;
if (Alen < Blen)
{
nmod_poly_zero(Q);
return;
}
if (Q == A || Q == B)
{
nmod_poly_init2(tQ, A->mod.n, Alen - Blen + 1);
q = tQ->coeffs;
}
else
{
nmod_poly_fit_length(Q, Alen - Blen + 1);
q = Q->coeffs;
}
_nmod_poly_div_divconquer(q, A->coeffs, Alen,
B->coeffs, Blen, A->mod);
if (Q == A || Q == B)
{
nmod_poly_swap(tQ, Q);
nmod_poly_clear(tQ);
}
Q->length = Alen - Blen + 1;
}
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