pqc/external/flint-2.4.3/fmpz_poly/divrem_divconquer.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
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_divrem_divconquer(fmpz * Q, fmpz * R,
const fmpz * A, slong lenA,
const fmpz * B, slong lenB)
{
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_poly_divrem_divconquer_recursive(Q, d1q1, W, p1, d1, n1);
/*
Compute d2q1 = Q d2, of length lenB - 1
*/
if (n1 >= n2)
_fmpz_poly_mul(d2q1, Q, n1, d2, n2);
else
_fmpz_poly_mul(d2q1, d2, n2, Q, n1);
/*
Compute BQ = d1q1 * x^n1 + d2q1, of length lenB - 1;
then compute R = A - BQ
*/
_fmpz_vec_swap(R, d2q1, n2);
_fmpz_vec_add(R + n2, R + n2, d2q1 + n2, n1 - 1);
_fmpz_vec_sub(R, A, R, lenA);
_fmpz_vec_clear(W, (2 * n1 - 1) + lenB - 1);
}
else /* lenA = 2 * lenB - 1 */
{
fmpz * W = _fmpz_vec_init(lenA);
_fmpz_poly_divrem_divconquer_recursive(Q, R, W, A, B, lenB);
_fmpz_vec_sub(R, A, R, lenA);
_fmpz_vec_clear(W, lenA);
}
}
void _fmpz_poly_divrem_divconquer(fmpz *Q, fmpz *R,
const fmpz *A, slong lenA,
const fmpz *B, slong lenB)
{
if (lenA <= 2 * lenB - 1)
{
__fmpz_poly_divrem_divconquer(Q, R, A, lenA, B, lenB);
}
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_poly_divrem_divconquer_recursive(Q + shift, QB,
W, R + shift, B, lenB);
_fmpz_vec_sub(R + shift, R + shift, QB, n);
lenA -= lenB;
}
if (lenA >= lenB)
{
__fmpz_poly_divrem_divconquer(Q, W, R, lenA, B, lenB);
_fmpz_vec_swap(W, R, lenA);
}
_fmpz_vec_clear(W, 2 * n);
}
}
void
fmpz_poly_divrem_divconquer(fmpz_poly_t Q, fmpz_poly_t R,
const fmpz_poly_t A, const fmpz_poly_t B)
{
const slong lenA = A->length;
const slong lenB = B->length;
fmpz_poly_t tQ, tR;
fmpz *q, *r;
if (lenB == 0)
{
flint_printf("Exception (fmpz_poly_divrem_divconquer). Division by zero.\n");
abort();
}
if (lenA < lenB)
{
fmpz_poly_set(R, A);
fmpz_poly_zero(Q);
return;
}
if (Q == A || Q == B)
{
fmpz_poly_init2(tQ, lenA - lenB + 1);
q = tQ->coeffs;
}
else
{
fmpz_poly_fit_length(Q, lenA - lenB + 1);
q = Q->coeffs;
}
if (R == A || R == B)
{
fmpz_poly_init2(tR, lenA);
r = tR->coeffs;
}
else
{
fmpz_poly_fit_length(R, lenA);
r = R->coeffs;
}
_fmpz_poly_divrem_divconquer(q, r, A->coeffs, lenA, B->coeffs, lenB);
if (Q == A || Q == B)
{
_fmpz_poly_set_length(tQ, lenA - lenB + 1);
fmpz_poly_swap(tQ, Q);
fmpz_poly_clear(tQ);
}
else
_fmpz_poly_set_length(Q, lenA - lenB + 1);
if (R == A || R == B)
{
_fmpz_poly_set_length(tR, lenA);
fmpz_poly_swap(tR, R);
fmpz_poly_clear(tR);
}
else
_fmpz_poly_set_length(R, lenA);
_fmpz_poly_normalise(Q);
_fmpz_poly_normalise(R);
}