pqc/external/flint-2.4.3/nmod_poly_mat/inv.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) 2010 Fredrik Johansson
******************************************************************************/
#include "flint.h"
#include "nmod_poly.h"
#include "nmod_poly_mat.h"
#include "perm.h"
#define E nmod_poly_mat_entry
int
nmod_poly_mat_inv(nmod_poly_mat_t Ainv, nmod_poly_t den,
const nmod_poly_mat_t A)
{
slong n = nmod_poly_mat_nrows(A);
if (n == 0)
{
nmod_poly_one(den);
return 1;
}
else if (n == 1)
{
nmod_poly_set(den, E(A, 0, 0));
nmod_poly_one(E(Ainv, 0, 0));
return !nmod_poly_is_zero(den);
}
else if (n == 2)
{
nmod_poly_mat_det(den, A);
if (nmod_poly_is_zero(den))
{
return 0;
}
else if (Ainv == A)
{
nmod_poly_swap(E(A, 0, 0), E(A, 1, 1));
nmod_poly_neg(E(A, 0, 1), E(A, 0, 1));
nmod_poly_neg(E(A, 1, 0), E(A, 1, 0));
return 1;
}
else
{
nmod_poly_set(E(Ainv, 0, 0), E(A, 1, 1));
nmod_poly_set(E(Ainv, 1, 1), E(A, 0, 0));
nmod_poly_neg(E(Ainv, 0, 1), E(A, 0, 1));
nmod_poly_neg(E(Ainv, 1, 0), E(A, 1, 0));
return 1;
}
}
else
{
nmod_poly_mat_t LU, I;
slong * perm;
int result;
perm = _perm_init(n);
nmod_poly_mat_init_set(LU, A);
result = (nmod_poly_mat_fflu(LU, den, perm, LU, 1) == n);
if (result)
{
nmod_poly_mat_init(I, n, n, nmod_poly_mat_modulus(A));
nmod_poly_mat_one(I);
nmod_poly_mat_solve_fflu_precomp(Ainv, perm, LU, I);
nmod_poly_mat_clear(I);
}
else
nmod_poly_zero(den);
if (_perm_parity(perm, n))
{
nmod_poly_mat_neg(Ainv, Ainv);
nmod_poly_neg(den, den);
}
_perm_clear(perm);
nmod_poly_mat_clear(LU);
return result;
}
}