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/*=============================================================================
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) 2012 Sebastian Pancratz
******************************************************************************/
#include "nmod_poly.h"
slong _nmod_poly_gcd(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;
if (lenA < cutoff)
return _nmod_poly_gcd_euclidean(G, A, lenA, B, lenB, mod);
else
return _nmod_poly_gcd_hgcd(G, A, lenA, B, lenB, mod);
}
void nmod_poly_gcd(nmod_poly_t G,
const nmod_poly_t A, const nmod_poly_t B)
{
if (A->length < B->length)
{
nmod_poly_gcd(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(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);
}
}
}
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