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

157 lines
4.7 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, 2012 Sebastian Pancratz
******************************************************************************/
#include <stdlib.h>
#include "nmod_poly.h"
#include "mpn_extras.h"
#define __set(B, lenB, A, lenA) \
do { \
_nmod_vec_set((B), (A), (lenA)); \
(lenB) = (lenA); \
} while (0)
#define __rem(R, lenR, A, lenA, B, lenB) \
do { \
if ((lenA) >= (lenB)) \
{ \
_nmod_poly_rem((R), (A), (lenA), (B), (lenB), mod); \
(lenR) = (lenB) - 1; \
MPN_NORM((R), (lenR)); \
} \
else \
{ \
_nmod_vec_set((R), (A), (lenA)); \
(lenR) = (lenA); \
} \
} while (0)
/*
XXX: Incidentally, this implementation currently supports aliasing.
But since this may change in the future, no function other than
nmod_poly_gcd_hgcd() should rely on this.
*/
slong _nmod_poly_gcd_hgcd(mp_ptr G, mp_srcptr A, slong lenA,
mp_srcptr B, slong lenB, nmod_t mod)
{
const slong cutoff = FLINT_BIT_COUNT(mod.n) <= 8 ?
NMOD_POLY_SMALL_GCD_CUTOFF : NMOD_POLY_GCD_CUTOFF;
mp_ptr J = _nmod_vec_init(2 * lenB);
mp_ptr R = J + lenB;
slong lenG, lenJ, lenR;
__rem(R, lenR, A, lenA, B, lenB);
if (lenR == 0)
{
__set(G, lenG, B, lenB);
}
else
{
_nmod_poly_hgcd(NULL, NULL, G, &(lenG), J, &(lenJ), B, lenB, R, lenR, mod);
while (lenJ != 0)
{
__rem(R, lenR, G, lenG, J, lenJ);
if (lenR == 0)
{
__set(G, lenG, J, lenJ);
break;
}
if (lenJ < cutoff)
{
lenG = _nmod_poly_gcd_euclidean(G, J, lenJ, R, lenR, mod);
break;
}
_nmod_poly_hgcd(NULL, NULL, G, &(lenG), J, &(lenJ), J, lenJ, R, lenR, mod);
}
}
_nmod_vec_clear(J);
return lenG;
}
void nmod_poly_gcd_hgcd(nmod_poly_t G,
const nmod_poly_t A, const nmod_poly_t B)
{
if (A->length < B->length)
{
nmod_poly_gcd_hgcd(G, B, A);
}
else /* lenA >= lenB >= 0 */
{
slong lenA = A->length, lenB = B->length, lenG;
nmod_poly_t tG;
mp_ptr g;
if (lenA == 0) /* lenA = lenB = 0 */
{
nmod_poly_zero(G);
}
else if (lenB == 0) /* lenA > lenB = 0 */
{
nmod_poly_make_monic(G, A);
}
else /* lenA >= lenB >= 1 */
{
if (G == A || G == B)
{
nmod_poly_init2(tG, A->mod.n, FLINT_MIN(lenA, lenB));
g = tG->coeffs;
}
else
{
nmod_poly_fit_length(G, FLINT_MIN(lenA, lenB));
g = G->coeffs;
}
lenG = _nmod_poly_gcd_hgcd(g, A->coeffs, lenA,
B->coeffs, lenB, A->mod);
if (G == A || G == B)
{
nmod_poly_swap(tG, G);
nmod_poly_clear(tG);
}
G->length = lenG;
if (G->length == 1)
G->coeffs[0] = 1;
else
nmod_poly_make_monic(G, G);
}
}
}
#undef __set
#undef __rem