/*============================================================================= 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) 2011 Sebastian Pancratz ******************************************************************************/ #include #include "flint.h" #include "fmpz_mod_poly.h" void _fmpz_mod_poly_compose_horner(fmpz *res, const fmpz *poly1, slong len1, const fmpz *poly2, slong len2, const fmpz_t p) { if (len1 == 1 || len2 == 0) { fmpz_set(res, poly1); } else { const slong alloc = (len1 - 1) * (len2 - 1) + 1; slong i = len1 - 1, lenr = len2; fmpz * t = _fmpz_vec_init(alloc); /* Perform the first two steps as one, "res = a(m) * poly2 + a(m-1)". */ { _fmpz_mod_poly_scalar_mul_fmpz(res, poly2, len2, poly1 + i, p); i--; fmpz_add(res, res, poly1 + i); if (fmpz_cmpabs(res, p) >= 0) fmpz_sub(res, res, p); } while (i > 0) { i--; _fmpz_mod_poly_mul(t, res, lenr, poly2, len2, p); lenr += len2 - 1; _fmpz_mod_poly_add(res, t, lenr, poly1 + i, 1, p); } _fmpz_vec_clear(t, alloc); } } void fmpz_mod_poly_compose_horner(fmpz_mod_poly_t res, const fmpz_mod_poly_t poly1, const fmpz_mod_poly_t poly2) { const slong len1 = poly1->length; const slong len2 = poly2->length; if (len1 == 0) { fmpz_mod_poly_zero(res); } else if (len1 == 1 || len2 == 0) { fmpz_mod_poly_set_fmpz(res, poly1->coeffs); } else { const slong lenr = (len1 - 1) * (len2 - 1) + 1; if ((res != poly1) && (res != poly2)) { fmpz_mod_poly_fit_length(res, lenr); _fmpz_mod_poly_compose_horner(res->coeffs, poly1->coeffs, len1, poly2->coeffs, len2, &(res->p)); } else { fmpz *t = _fmpz_vec_init(lenr); _fmpz_mod_poly_compose_horner(t, poly1->coeffs, len1, poly2->coeffs, len2, &(res->p)); _fmpz_vec_clear(res->coeffs, res->alloc); res->coeffs = t; res->alloc = lenr; res->length = lenr; } _fmpz_mod_poly_set_length(res, lenr); _fmpz_mod_poly_normalise(res); } }