122 lines
3.3 KiB
C
122 lines
3.3 KiB
C
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/*=============================================================================
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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, 2011 Sebastian Pancratz
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Copyright (C) 2013 William Hart
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******************************************************************************/
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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_poly.h"
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void
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_fmpz_poly_preinvert(fmpz * Binv, const fmpz * B, slong len)
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{
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if (len == 1) /* B is +-1 */
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{
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fmpz_set(Binv, B);
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}
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else
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{
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const slong alloc = len + FLINT_MAX(len, 3 * FMPZ_POLY_INV_NEWTON_CUTOFF);
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slong *a, i, m, n = len;
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fmpz *T, *W;
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T = _fmpz_vec_init(alloc);
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W = T + len;
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for (i = 1; (WORD(1) << i) < n; i++) ;
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a = (slong *) flint_malloc(i * sizeof(slong));
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a[i = 0] = n;
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while (n >= FMPZ_POLY_INV_NEWTON_CUTOFF)
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a[++i] = (n = (n + 1) / 2);
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if (len != n)
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_fmpz_poly_reverse(T, B, len, len); /* only reverse if it ... */
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/* Base case */
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{
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fmpz *Brev = W + 2 * FMPZ_POLY_INV_NEWTON_CUTOFF;
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if (len != n)
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_fmpz_poly_reverse(Brev, T, n, n); /* ... won't be undone */
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else Brev = (fmpz *) B;
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_fmpz_vec_zero(W, 2*n - 2);
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fmpz_one(W + (2*n - 2));
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_fmpz_poly_div_basecase(Binv, W, W, 2*n - 1, Brev, n);
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_fmpz_poly_reverse(Binv, Binv, n, n);
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}
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for (i--; i >= 0; i--)
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{
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m = n;
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n = a[i];
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_fmpz_poly_mullow(W, T, n, Binv, m, n);
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_fmpz_poly_mullow(Binv + m, Binv, m, W + m, n - m, n - m);
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_fmpz_vec_neg(Binv + m, Binv + m, n - m);
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}
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_fmpz_vec_clear(T, alloc);
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flint_free(a);
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}
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}
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void
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fmpz_poly_preinvert(fmpz_poly_t B_inv, const fmpz_poly_t B)
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{
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slong n = B->length;
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fmpz_poly_t temp;
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fmpz * Binv_coeffs;
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if (n == 0)
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{
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flint_printf("Exception (fmpz_poly_preinvert). Division by zero.\n");
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abort();
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}
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if (B == B_inv)
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{
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fmpz_poly_init2(temp, n);
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Binv_coeffs = temp->coeffs;
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} else
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{
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fmpz_poly_fit_length(B_inv, n);
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Binv_coeffs = B_inv->coeffs;
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}
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_fmpz_poly_preinvert(Binv_coeffs, B->coeffs, n);
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if (B == B_inv)
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{
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_fmpz_poly_set_length(temp, n);
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fmpz_poly_swap(B_inv, temp);
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fmpz_poly_clear(temp);
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} else
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_fmpz_poly_set_length(B_inv, n);
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/* no need to normalise */
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}
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