162 lines
4.3 KiB
C
162 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) 2010 Sebastian Pancratz
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Copyright (C) 2010 William Hart
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Copyright (C) 2011 Fredrik Johansson
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Copyright (C) 2012 Lina Kulakova
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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_vec.h"
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#include "fmpz_mod_poly.h"
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#include "ulong_extras.h"
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void
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_fmpz_mod_poly_powmod_ui_binexp(fmpz * res, const fmpz * poly,
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ulong e, const fmpz * f, slong lenf, const fmpz_t p)
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{
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fmpz * T, * Q;
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fmpz_t invf;
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slong lenT, lenQ;
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int i;
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if (lenf == 2)
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{
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fmpz_powm_ui(res, poly, e, p);
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return;
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}
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lenT = 2 * lenf - 3;
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lenQ = FLINT_MAX(lenT - lenf + 1, 1);
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T = _fmpz_vec_init(lenT + lenQ);
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Q = T + lenT;
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fmpz_init(invf);
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fmpz_invmod(invf, f + lenf - 1, p);
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_fmpz_vec_set(res, poly, lenf - 1);
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for (i = ((int) FLINT_BIT_COUNT(e) - 2); i >= 0; i--)
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{
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_fmpz_mod_poly_sqr(T, res, lenf - 1, p);
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_fmpz_mod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, invf, p);
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if (e & (UWORD(1) << i))
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{
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_fmpz_mod_poly_mul(T, res, lenf - 1, poly, lenf - 1, p);
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_fmpz_mod_poly_divrem(Q, res, T, 2 * lenf - 3, f, lenf, invf, p);
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}
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}
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fmpz_clear(invf);
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_fmpz_vec_clear(T, lenT + lenQ);
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}
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void
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fmpz_mod_poly_powmod_ui_binexp(fmpz_mod_poly_t res,
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const fmpz_mod_poly_t poly, ulong e,
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const fmpz_mod_poly_t f)
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{
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fmpz * q;
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slong len = poly->length;
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slong lenf = f->length;
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slong trunc = lenf - 1;
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int qcopy = 0;
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if (lenf == 0)
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{
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flint_printf("Exception (fmpz_mod_poly_powmod). Divide by zero\n");
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abort();
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}
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if (len >= lenf)
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{
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fmpz_mod_poly_t t, r;
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fmpz_mod_poly_init(t, &res->p);
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fmpz_mod_poly_init(r, &res->p);
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fmpz_mod_poly_divrem(t, r, poly, f);
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fmpz_mod_poly_powmod_ui_binexp(res, r, e, f);
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fmpz_mod_poly_clear(t);
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fmpz_mod_poly_clear(r);
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return;
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}
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if (e <= 2)
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{
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if (e == UWORD(0))
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{
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fmpz_mod_poly_fit_length(res, 1);
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fmpz_one(res->coeffs);
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_fmpz_mod_poly_set_length(res, 1);
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}
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else if (e == UWORD(1))
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{
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fmpz_mod_poly_set(res, poly);
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}
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else
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fmpz_mod_poly_mulmod(res, poly, poly, f);
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return;
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}
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if (lenf == 1 || len == 0)
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{
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fmpz_mod_poly_zero(res);
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return;
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}
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if (len < trunc)
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{
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q = _fmpz_vec_init(trunc);
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_fmpz_vec_set(q, poly->coeffs, len);
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_fmpz_vec_zero(q + len, trunc - len);
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qcopy = 1;
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} else
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q = poly->coeffs;
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if ((res == poly && !qcopy) || (res == f))
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{
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fmpz_mod_poly_t t;
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fmpz_mod_poly_init2(t, &poly->p, 2 * lenf - 3);
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_fmpz_mod_poly_powmod_ui_binexp(t->coeffs,
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q, e, f->coeffs, lenf, &poly->p);
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fmpz_mod_poly_swap(res, t);
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fmpz_mod_poly_clear(t);
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}
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else
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{
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fmpz_mod_poly_fit_length(res, 2 * lenf - 3);
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_fmpz_mod_poly_powmod_ui_binexp(res->coeffs,
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q, e, f->coeffs, lenf, &poly->p);
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}
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if (qcopy)
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_fmpz_vec_clear(q, trunc);
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_fmpz_mod_poly_set_length(res, trunc);
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_fmpz_mod_poly_normalise(res);
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}
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