/* Copyright (C) 2008, 2009, 2011 William Hart Copyright (C) 2012 Fredrik Johansson This file is part of FLINT. FLINT is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License (LGPL) as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. See . */ #include #include #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) { if (nmod_poly_modulus(B) == 1) { nmod_poly_set(Q, A); return; } else { flint_printf("Exception (nmod_poly_div_divconquer). Division by zero.\n"); flint_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; }