163 lines
4.3 KiB
C
163 lines
4.3 KiB
C
/*=============================================================================
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This file is part of FLINT.
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FLINT 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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FLINT 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 FLINT; 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) 2008, 2009, 2011 William Hart
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Copyright (C) 2012 Fredrik Johansson
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******************************************************************************/
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#include <stdlib.h>
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#include <gmp.h>
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#include "flint.h"
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#include "nmod_vec.h"
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#include "nmod_poly.h"
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static void
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__nmod_poly_div_divconquer(mp_ptr Q, mp_srcptr A, slong lenA,
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mp_srcptr B, slong lenB, nmod_t mod)
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{
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if (lenA < 2 * lenB - 1)
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{
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/*
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Convert unbalanced division into a 2 n1 - 1 by n1 division
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*/
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const slong n1 = lenA - lenB + 1;
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const slong n2 = lenB - n1;
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mp_srcptr p1 = A + n2;
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mp_srcptr d1 = B + n2;
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mp_ptr V = _nmod_vec_init(n1 - 1 + NMOD_DIVREM_DC_ITCH(n1, mod));
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mp_ptr W = V + NMOD_DIVREM_DC_ITCH(n1, mod);
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_nmod_poly_div_divconquer_recursive(Q, W, V, p1, d1, n1, mod);
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_nmod_vec_clear(V);
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}
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else /* lenA = 2 * lenB - 1 */
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{
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mp_ptr V = _nmod_vec_init(lenB - 1 + NMOD_DIVREM_DC_ITCH(lenB, mod));
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mp_ptr W = V + NMOD_DIVREM_DC_ITCH(lenB, mod);
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_nmod_poly_div_divconquer_recursive(Q, W, V, A, B, lenB, mod);
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_nmod_vec_clear(V);
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}
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}
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/* needed due to partial overlap */
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static void
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_nmod_vec_sub_dec(mp_ptr a, mp_srcptr b, mp_srcptr c, slong n, nmod_t mod)
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{
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slong i;
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for (i = n - 1; i >= 0; i--)
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a[i] = n_submod(b[i], c[i], mod.n);
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}
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void
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_nmod_poly_div_divconquer(mp_ptr Q, mp_srcptr A, slong lenA,
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mp_srcptr B, slong lenB, nmod_t mod)
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{
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if (lenA <= 2 * lenB - 1)
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{
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__nmod_poly_div_divconquer(Q, A, lenA, B, lenB, mod);
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}
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else /* lenA > 2 * lenB - 1 */
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{
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mp_ptr S, T, V, R;
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slong shift, next, n = 2 * lenB - 1;
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S = _nmod_vec_init(2 * n + (lenB - 1) + NMOD_DIVREM_DC_ITCH(lenB, mod));
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T = S + n;
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R = T + n;
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V = R + (lenB - 1);
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shift = lenA - n;
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_nmod_vec_set(S, A + shift, n);
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while (lenA >= n)
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{
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shift = lenA - n;
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_nmod_poly_divrem_divconquer_recursive(Q + shift, T, R, V, S, B, lenB, mod);
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next = FLINT_MIN(lenB, shift);
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_nmod_vec_sub_dec(S + next, S, T, lenB - 1, mod);
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_nmod_vec_set(S, A + shift - next, next);
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lenA -= lenB;
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}
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if (lenA >= lenB)
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__nmod_poly_div_divconquer(Q, S, lenA, B, lenB, mod);
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_nmod_vec_clear(S);
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}
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}
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void
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nmod_poly_div_divconquer(nmod_poly_t Q,
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const nmod_poly_t A, const nmod_poly_t B)
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{
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nmod_poly_t tQ;
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mp_ptr q;
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slong Alen, Blen;
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Blen = B->length;
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if (Blen == 0)
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{
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flint_printf("Exception (nmod_poly_div_divconquer). Division by zero.\n");
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abort();
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}
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Alen = A->length;
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if (Alen < Blen)
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{
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nmod_poly_zero(Q);
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return;
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}
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if (Q == A || Q == B)
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{
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nmod_poly_init2(tQ, A->mod.n, Alen - Blen + 1);
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q = tQ->coeffs;
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}
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else
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{
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nmod_poly_fit_length(Q, Alen - Blen + 1);
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q = Q->coeffs;
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}
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_nmod_poly_div_divconquer(q, A->coeffs, Alen,
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B->coeffs, Blen, A->mod);
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if (Q == A || Q == B)
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{
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nmod_poly_swap(tQ, Q);
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nmod_poly_clear(tQ);
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}
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Q->length = Alen - Blen + 1;
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}
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