157 lines
4.2 KiB
C
157 lines
4.2 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 William Hart
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Copyright (C) 2010 Sebastian Pancratz
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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 "fmpz.h"
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#include "fmpz_vec.h"
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#include "fmpz_poly.h"
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static void
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__fmpz_poly_div_divconquer(fmpz * Q, const fmpz * A, slong lenA,
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const fmpz * B, slong lenB)
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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 q1 - 1 by q1 division
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*/
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const slong q1 = lenA - lenB + 1;
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const slong q2 = lenB - q1;
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fmpz * temp = _fmpz_vec_init(2 * q1 - 1);
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_fmpz_poly_div_divconquer_recursive(Q, temp, A + q2, B + q2, q1);
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_fmpz_vec_clear(temp, 2 * q1 - 1);
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}
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else /* lenA = 2 lenB - 1 */
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{
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fmpz * temp = _fmpz_vec_init(lenA);
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_fmpz_poly_div_divconquer_recursive(Q, temp, A, B, lenB);
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_fmpz_vec_clear(temp, lenA);
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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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_fmpz_vec_sub_dec(fmpz * a, const fmpz * b, const fmpz * c, slong n)
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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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fmpz_sub(a + i, b + i, c + i);
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}
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void _fmpz_poly_div_divconquer(fmpz *Q,
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const fmpz *A, slong lenA,
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const fmpz *B, slong lenB)
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{
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if (lenA <= 2 * lenB - 1)
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{
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__fmpz_poly_div_divconquer(Q, A, lenA, B, lenB);
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}
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else /* lenA > 2 * lenB - 1 */
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{
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fmpz *S, *T;
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slong shift, next, n = 2 * lenB - 1;
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S = _fmpz_vec_init(2 * n);
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T = S + n;
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/* To avoid copying all of A, we let S be a window of the
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remainder, taking up to n coefficients at a time */
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shift = lenA - n;
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_fmpz_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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_fmpz_poly_divremlow_divconquer_recursive(Q + shift, T, S, B, lenB);
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next = FLINT_MIN(lenB, shift);
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_fmpz_vec_sub_dec(S + next, S, T, lenB - 1);
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_fmpz_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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__fmpz_poly_div_divconquer(Q, S, lenA, B, lenB);
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_fmpz_vec_clear(S, 2 * n);
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}
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}
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void
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fmpz_poly_div_divconquer(fmpz_poly_t Q,
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const fmpz_poly_t A, const fmpz_poly_t B)
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{
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const slong lenA = A->length;
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const slong lenB = B->length;
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fmpz_poly_t t;
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fmpz *q;
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if (lenB == 0)
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{
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flint_printf("Exception (fmpz_poly_div_divconquer). Division by zero.\n");
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abort();
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}
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if (lenA < lenB)
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{
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fmpz_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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fmpz_poly_init2(t, lenA - lenB + 1);
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q = t->coeffs;
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}
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else
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{
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fmpz_poly_fit_length(Q, lenA - lenB + 1);
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q = Q->coeffs;
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}
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_fmpz_poly_div_divconquer(q, A->coeffs, lenA, B->coeffs, lenB);
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if (Q == A || Q == B)
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{
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_fmpz_poly_set_length(t, lenA - lenB + 1);
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fmpz_poly_swap(t, Q);
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fmpz_poly_clear(t);
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}
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else
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_fmpz_poly_set_length(Q, lenA - lenB + 1);
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_fmpz_poly_normalise(Q);
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}
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