/*============================================================================= 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 William Hart ******************************************************************************/ #include #include "flint.h" #include "fmpz.h" #include "fmpz_vec.h" #include "fmpz_poly.h" /* Assumes poly1 and poly2 are not length 0 and 0 < n <= len1 + len2 - 1. */ void _fmpz_poly_mullow_classical(fmpz * res, const fmpz * poly1, slong len1, const fmpz * poly2, slong len2, slong n) { if ((len1 == 1 && len2 == 1) || n == 1) /* Special case if the length of output is 1 */ { fmpz_mul(res, poly1, poly2); } else /* Ordinary case */ { slong i; /* Set res[i] = poly1[i]*poly2[0] */ _fmpz_vec_scalar_mul_fmpz(res, poly1, FLINT_MIN(len1, n), poly2); /* Set res[i+len1-1] = in1[len1-1]*in2[i] */ if (n > len1) _fmpz_vec_scalar_mul_fmpz(res + len1, poly2 + 1, n - len1, poly1 + len1 - 1); /* out[i+j] += in1[i]*in2[j] */ for (i = 0; i < FLINT_MIN(len1, n) - 1; i++) _fmpz_vec_scalar_addmul_fmpz(res + i + 1, poly2 + 1, FLINT_MIN(len2, n - i) - 1, poly1 + i); } } void fmpz_poly_mullow_classical(fmpz_poly_t res, const fmpz_poly_t poly1, const fmpz_poly_t poly2, slong n) { slong len_out; if (poly1->length == 0 || poly2->length == 0 || n == 0) { fmpz_poly_zero(res); return; } len_out = poly1->length + poly2->length - 1; if (n > len_out) n = len_out; if (res == poly1 || res == poly2) { fmpz_poly_t t; fmpz_poly_init2(t, n); _fmpz_poly_mullow_classical(t->coeffs, poly1->coeffs, poly1->length, poly2->coeffs, poly2->length, n); fmpz_poly_swap(res, t); fmpz_poly_clear(t); } else { fmpz_poly_fit_length(res, n); _fmpz_poly_mullow_classical(res->coeffs, poly1->coeffs, poly1->length, poly2->coeffs, poly2->length, n); } _fmpz_poly_set_length(res, n); _fmpz_poly_normalise(res); }