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

197 lines
5.2 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, 2011 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "fmpz_vec.h"
#include "fmpz_mod_poly.h"
static void
__fmpz_mod_poly_divrem_divconquer(fmpz * Q, fmpz * R,
const fmpz * A, slong lenA, const fmpz * B, slong lenB,
const fmpz_t invB, const fmpz_t p)
{
if (lenA < 2 * lenB - 1)
{
/*
Convert unbalanced division into a 2 n1 - 1 by n1 division
*/
const slong n1 = lenA - lenB + 1;
const slong n2 = lenB - n1;
const fmpz * p1 = A + n2;
const fmpz * d1 = B + n2;
const fmpz * d2 = B;
fmpz * W = _fmpz_vec_init((2 * n1 - 1) + lenB - 1);
fmpz * d1q1 = R + n2;
fmpz * d2q1 = W + (2 * n1 - 1);
_fmpz_mod_poly_divrem_divconquer_recursive(Q, d1q1, W, p1, d1, n1,
invB, p);
/*
Compute d2q1 = Q d2, of length lenB - 1
*/
if (n1 >= n2)
_fmpz_mod_poly_mul(d2q1, Q, n1, d2, n2, p);
else
_fmpz_mod_poly_mul(d2q1, d2, n2, Q, n1, p);
/*
Compute BQ = d1q1 * x^n1 + d2q1, of length lenB - 1;
then compute R = A - BQ
*/
_fmpz_vec_swap(R, d2q1, n2);
_fmpz_mod_poly_add(R + n2, R + n2, n1 - 1, d2q1 + n2, n1 - 1, p);
_fmpz_mod_poly_sub(R, A, lenA, R, lenA, p);
_fmpz_vec_clear(W, (2 * n1 - 1) + lenB - 1);
}
else /* lenA = 2 * lenB - 1 */
{
fmpz * W = _fmpz_vec_init(lenA);
_fmpz_mod_poly_divrem_divconquer_recursive(Q, R, W,
A, B, lenB, invB, p);
_fmpz_mod_poly_sub(R, A, lenB - 1, R, lenB - 1, p);
_fmpz_vec_clear(W, lenA);
}
}
void _fmpz_mod_poly_divrem_divconquer(fmpz *Q, fmpz *R,
const fmpz *A, slong lenA, const fmpz *B, slong lenB,
const fmpz_t invB, const fmpz_t p)
{
if (lenA <= 2 * lenB - 1)
{
__fmpz_mod_poly_divrem_divconquer(Q, R, A, lenA, B, lenB, invB, p);
}
else /* lenA > 2 * lenB - 1 */
{
slong shift, n = 2 * lenB - 1;
fmpz *QB, *W;
_fmpz_vec_set(R, A, lenA);
W = _fmpz_vec_init(2 * n);
QB = W + n;
while (lenA >= n)
{
shift = lenA - n;
_fmpz_mod_poly_divrem_divconquer_recursive(Q + shift, QB,
W, R + shift, B, lenB, invB, p);
_fmpz_mod_poly_sub(R + shift, R + shift, n, QB, n, p);
lenA -= lenB;
}
if (lenA >= lenB)
{
__fmpz_mod_poly_divrem_divconquer(Q, W, R, lenA, B, lenB, invB, p);
_fmpz_vec_swap(W, R, lenA);
}
_fmpz_vec_clear(W, 2 * n);
}
}
void
fmpz_mod_poly_divrem_divconquer(fmpz_mod_poly_t Q, fmpz_mod_poly_t R,
const fmpz_mod_poly_t A, const fmpz_mod_poly_t B)
{
const slong lenA = A->length;
const slong lenB = B->length;
const slong lenQ = lenA - lenB + 1;
fmpz *q, *r;
fmpz_t invB;
if (lenA < lenB)
{
fmpz_mod_poly_set(R, A);
fmpz_mod_poly_zero(Q);
return;
}
fmpz_init(invB);
fmpz_invmod(invB, fmpz_mod_poly_lead(B), &(B->p));
if (Q == A || Q == B)
{
q = _fmpz_vec_init(lenQ);
}
else
{
fmpz_mod_poly_fit_length(Q, lenQ);
q = Q->coeffs;
}
if (R == A || R == B)
{
r = _fmpz_vec_init(lenA);
}
else
{
fmpz_mod_poly_fit_length(R, lenA);
r = R->coeffs;
}
_fmpz_mod_poly_divrem_divconquer(q, r, A->coeffs, lenA,
B->coeffs, lenB, invB, &(B->p));
if (Q == A || Q == B)
{
_fmpz_vec_clear(Q->coeffs, Q->alloc);
Q->coeffs = q;
Q->alloc = lenQ;
Q->length = lenQ;
}
else
{
_fmpz_mod_poly_set_length(Q, lenQ);
}
if (R == A || R == B)
{
_fmpz_vec_clear(R->coeffs, R->alloc);
R->coeffs = r;
R->alloc = lenA;
R->length = lenA;
}
_fmpz_mod_poly_set_length(R, lenB - 1);
_fmpz_mod_poly_normalise(R);
fmpz_clear(invB);
}