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

152 lines
4.3 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) 2011 William Hart
Copyright (C) 2011 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include "fmpz_vec.h"
#include "fmpz_mod_poly.h"
slong _fmpz_mod_poly_gcd_euclidean(fmpz *G, const fmpz *A, slong lenA,
const fmpz *B, slong lenB,
const fmpz_t invB, const fmpz_t p)
{
if (lenB == 1)
{
fmpz_one(G);
return 1;
}
else /* lenA >= lenB > 1 */
{
const slong lenW = FLINT_MAX(lenA - lenB + 1, lenB) + lenA + 2 * lenB;
fmpz_t invR3;
fmpz *Q, *R1, *R2, *R3, *T, *W;
slong lenR2, lenR3;
W = _fmpz_vec_init(lenW);
Q = W;
R1 = W + FLINT_MAX(lenA - lenB + 1, lenB);
R2 = R1 + lenA;
R3 = R2 + lenB;
_fmpz_mod_poly_divrem(Q, R1, A, lenA, B, lenB, invB, p);
lenR3 = lenB - 1;
FMPZ_VEC_NORM(R1, lenR3);
if (lenR3 == 0)
{
_fmpz_vec_set(G, B, lenB);
_fmpz_vec_clear(W, lenW);
return lenB;
}
fmpz_init(invR3);
T = R3;
R3 = R1;
R1 = T;
_fmpz_vec_set(R2, B, lenB);
lenR2 = lenB;
do
{
fmpz_invmod(invR3, R3 + (lenR3 - 1), p);
_fmpz_mod_poly_divrem(Q, R1, R2, lenR2, R3, lenR3, invR3, p);
lenR2 = lenR3--;
FMPZ_VEC_NORM(R1, lenR3);
T = R2; R2 = R3; R3 = R1; R1 = T;
}
while (lenR3 > 0);
_fmpz_vec_set(G, R2, lenR2);
_fmpz_vec_clear(W, lenW);
fmpz_clear(invR3);
return lenR2;
}
}
void fmpz_mod_poly_gcd_euclidean(fmpz_mod_poly_t G,
const fmpz_mod_poly_t A,
const fmpz_mod_poly_t B)
{
if (A->length < B->length)
{
fmpz_mod_poly_gcd_euclidean(G, B, A);
}
else /* lenA >= lenB >= 0 */
{
const slong lenA = A->length, lenB = B->length;
slong lenG;
fmpz *g;
if (lenA == 0) /* lenA = lenB = 0 */
{
fmpz_mod_poly_zero(G);
}
else if (lenB == 0) /* lenA > lenB = 0 */
{
fmpz_mod_poly_make_monic(G, A);
}
else /* lenA >= lenB >= 1 */
{
fmpz_t invB;
if (G == A || G == B)
{
g = _fmpz_vec_init(FLINT_MIN(lenA, lenB));
}
else
{
fmpz_mod_poly_fit_length(G, FLINT_MIN(lenA, lenB));
g = G->coeffs;
}
fmpz_init(invB);
fmpz_invmod(invB, fmpz_mod_poly_lead(B), &(B->p));
lenG = _fmpz_mod_poly_gcd_euclidean(g, A->coeffs, lenA,
B->coeffs, lenB, invB, &(B->p));
fmpz_clear(invB);
if (G == A || G == B)
{
_fmpz_vec_clear(G->coeffs, G->alloc);
G->coeffs = g;
G->alloc = FLINT_MIN(lenA, lenB);
G->length = FLINT_MIN(lenA, lenB);
}
_fmpz_mod_poly_set_length(G, lenG);
if (lenG == 1)
fmpz_one(G->coeffs);
else
fmpz_mod_poly_make_monic(G, G);
}
}
}