pqc/external/flint-2.4.3/fmpz_mat/rref_mod.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) 2011 Fredrik Johansson
Copyright (C) 2012 Lina Kulakova
******************************************************************************/
#include "fmpz_mat.h"
#define E(j,k) fmpz_mat_entry(A,j,k)
slong
fmpz_mat_rref_mod(slong * perm, fmpz_mat_t A, const fmpz_t p)
{
fmpz_t t, inv;
slong m, n, j, k, rank, r, pivot_row, pivot_col;
if (fmpz_mat_is_empty(A))
{
return 0;
}
m = A->r;
n = A->c;
rank = pivot_row = pivot_col = 0;
fmpz_init(t);
fmpz_init(inv);
while (pivot_row < m && pivot_col < n)
{
r = fmpz_mat_find_pivot_any(A, pivot_row, m, pivot_col);
if (r == -1)
{
pivot_col++;
continue;
}
else if (r != pivot_row)
{
fmpz_mat_swap_rows(A, perm, pivot_row, r);
}
rank++;
fmpz_invmod(inv, E(pivot_row, pivot_col), p);
/* pivot row */
for (k = pivot_col + 1; k < n; k++)
{
fmpz_mul(E(pivot_row, k), E(pivot_row, k), inv);
fmpz_mod(E(pivot_row, k), E(pivot_row, k), p);
}
fmpz_one(E(pivot_row, pivot_col));
/* other rows */
for (j = 0; j < m; j++)
{
if (j == pivot_row)
continue;
for (k = pivot_col + 1; k < n; k++)
{
fmpz_mul(t, E(j, pivot_col), E(pivot_row, k));
fmpz_sub(E(j, k), E(j, k), t);
fmpz_mod(E(j, k), E(j, k), p);
}
fmpz_zero(E(j, pivot_col));
}
pivot_row++;
pivot_col++;
}
fmpz_clear(inv);
fmpz_clear(t);
return rank;
}