62 lines
1.6 KiB
C
62 lines
1.6 KiB
C
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/*=============================================================================
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This file is part of FLINT.
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FLINT is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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FLINT is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with FLINT; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2011 Fredrik Johansson
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******************************************************************************/
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#include "perm.h"
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int
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_perm_parity(const slong *vec, slong n)
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{
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slong i, k;
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int * encountered;
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int parity;
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if (n <= 1)
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return 0;
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parity = 0;
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encountered = flint_calloc(n, sizeof(int));
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for (i = 0; i < n; i++)
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{
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if (encountered[i] != 0)
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{
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parity ^= 1;
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}
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else
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{
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k = i;
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do
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{
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k = vec[k];
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encountered[k] = 1;
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}
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while (k != i);
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}
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}
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flint_free(encountered);
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return parity;
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}
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