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