135 lines
3.2 KiB
C
135 lines
3.2 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) 2011 Fredrik Johansson
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******************************************************************************/
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#include <stdio.h>
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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 "ulong_extras.h"
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#include "fmpz.h"
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static __inline__ ulong rfac(ulong x, ulong b)
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{
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ulong i, c = x;
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for (i = 1; i < b; i++)
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c *= x + i;
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return c;
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}
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/* Assumes x positive, b > a. b must also be small enough to
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avoid integer overflow, which is no problem if the result
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is to fit in memory. */
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void
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_fmpz_rfac_ui(fmpz_t r, const fmpz_t x, ulong a, ulong b)
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{
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if (b - a == 1)
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{
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fmpz_add_ui(r, x, a);
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}
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else if ((*x <= COEFF_MAX) && (b - a < 60))
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{
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ulong step, bits, factors_per_limb;
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ulong y = *x;
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/* Bound size of largest factor */
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bits = FLINT_BIT_COUNT(y + a + b - 1);
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/* The result fits in a single limb */
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if ((b - a) * bits < FLINT_BITS)
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step = factors_per_limb = b - a;
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else
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{
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factors_per_limb = FLINT_BITS / bits;
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step = FLINT_MIN(b - a, factors_per_limb);
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}
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fmpz_set_ui(r, rfac(y + a, step));
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a += step;
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while (a < b)
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{
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step = FLINT_MIN(b - a, factors_per_limb);
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fmpz_mul_ui(r, r, rfac(y + a, step));
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a += step;
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}
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}
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else
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{
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fmpz_t t, u;
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ulong m = (a + b) / 2;
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fmpz_init(t);
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fmpz_init(u);
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_fmpz_rfac_ui(t, x, a, m);
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_fmpz_rfac_ui(u, x, m, b);
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fmpz_mul(r, t, u);
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fmpz_clear(t);
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fmpz_clear(u);
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}
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}
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void
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fmpz_rfac_ui(fmpz_t r, const fmpz_t x, ulong n)
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{
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if (n == 0)
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{
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fmpz_one(r);
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}
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else if (n == 1)
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{
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fmpz_set(r, x);
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}
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else if (fmpz_is_zero(x))
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{
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fmpz_zero(r);
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}
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else if (fmpz_sgn(x) < 0)
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{
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fmpz_t t;
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fmpz_init(t);
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fmpz_add_ui(t, x, n - 1);
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if (fmpz_sgn(t) >= 0)
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{
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fmpz_zero(r);
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}
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else
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{
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fmpz_neg(t, t);
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fmpz_rfac_ui(r, t, n);
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if (n % 2 == 1)
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fmpz_neg(r, r);
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}
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fmpz_clear(t);
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}
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else
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{
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_fmpz_rfac_ui(r, x, 0, n);
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}
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}
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