62 lines
1.6 KiB
C
62 lines
1.6 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 Fredrik Johansson
|
|
|
|
******************************************************************************/
|
|
|
|
#include "perm.h"
|
|
|
|
int
|
|
_perm_parity(const slong *vec, slong n)
|
|
{
|
|
slong i, k;
|
|
int * encountered;
|
|
int parity;
|
|
|
|
if (n <= 1)
|
|
return 0;
|
|
|
|
parity = 0;
|
|
encountered = flint_calloc(n, sizeof(int));
|
|
|
|
for (i = 0; i < n; i++)
|
|
{
|
|
if (encountered[i] != 0)
|
|
{
|
|
parity ^= 1;
|
|
}
|
|
else
|
|
{
|
|
k = i;
|
|
do
|
|
{
|
|
k = vec[k];
|
|
encountered[k] = 1;
|
|
}
|
|
while (k != i);
|
|
}
|
|
}
|
|
|
|
flint_free(encountered);
|
|
return parity;
|
|
}
|