pqc/external/flint-2.4.3/fmpz_poly/div_divconquer.c
2014-05-24 23:16:06 +02:00

157 lines
4.2 KiB
C

/*=============================================================================
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) 2008, 2009 William Hart
Copyright (C) 2010 Sebastian Pancratz
Copyright (C) 2012 Fredrik Johansson
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_poly.h"
static void
__fmpz_poly_div_divconquer(fmpz * Q, const fmpz * A, slong lenA,
const fmpz * B, slong lenB)
{
if (lenA < 2 * lenB - 1)
{
/*
Convert unbalanced division into a 2 q1 - 1 by q1 division
*/
const slong q1 = lenA - lenB + 1;
const slong q2 = lenB - q1;
fmpz * temp = _fmpz_vec_init(2 * q1 - 1);
_fmpz_poly_div_divconquer_recursive(Q, temp, A + q2, B + q2, q1);
_fmpz_vec_clear(temp, 2 * q1 - 1);
}
else /* lenA = 2 lenB - 1 */
{
fmpz * temp = _fmpz_vec_init(lenA);
_fmpz_poly_div_divconquer_recursive(Q, temp, A, B, lenB);
_fmpz_vec_clear(temp, lenA);
}
}
/* needed due to partial overlap */
static void
_fmpz_vec_sub_dec(fmpz * a, const fmpz * b, const fmpz * c, slong n)
{
slong i;
for (i = n - 1; i >= 0; i--)
fmpz_sub(a + i, b + i, c + i);
}
void _fmpz_poly_div_divconquer(fmpz *Q,
const fmpz *A, slong lenA,
const fmpz *B, slong lenB)
{
if (lenA <= 2 * lenB - 1)
{
__fmpz_poly_div_divconquer(Q, A, lenA, B, lenB);
}
else /* lenA > 2 * lenB - 1 */
{
fmpz *S, *T;
slong shift, next, n = 2 * lenB - 1;
S = _fmpz_vec_init(2 * n);
T = S + n;
/* To avoid copying all of A, we let S be a window of the
remainder, taking up to n coefficients at a time */
shift = lenA - n;
_fmpz_vec_set(S, A + shift, n);
while (lenA >= n)
{
shift = lenA - n;
_fmpz_poly_divremlow_divconquer_recursive(Q + shift, T, S, B, lenB);
next = FLINT_MIN(lenB, shift);
_fmpz_vec_sub_dec(S + next, S, T, lenB - 1);
_fmpz_vec_set(S, A + shift - next, next);
lenA -= lenB;
}
if (lenA >= lenB)
__fmpz_poly_div_divconquer(Q, S, lenA, B, lenB);
_fmpz_vec_clear(S, 2 * n);
}
}
void
fmpz_poly_div_divconquer(fmpz_poly_t Q,
const fmpz_poly_t A, const fmpz_poly_t B)
{
const slong lenA = A->length;
const slong lenB = B->length;
fmpz_poly_t t;
fmpz *q;
if (lenB == 0)
{
flint_printf("Exception (fmpz_poly_div_divconquer). Division by zero.\n");
abort();
}
if (lenA < lenB)
{
fmpz_poly_zero(Q);
return;
}
if (Q == A || Q == B)
{
fmpz_poly_init2(t, lenA - lenB + 1);
q = t->coeffs;
}
else
{
fmpz_poly_fit_length(Q, lenA - lenB + 1);
q = Q->coeffs;
}
_fmpz_poly_div_divconquer(q, A->coeffs, lenA, B->coeffs, lenB);
if (Q == A || Q == B)
{
_fmpz_poly_set_length(t, lenA - lenB + 1);
fmpz_poly_swap(t, Q);
fmpz_poly_clear(t);
}
else
_fmpz_poly_set_length(Q, lenA - lenB + 1);
_fmpz_poly_normalise(Q);
}