60 lines
1.5 KiB
C
60 lines
1.5 KiB
C
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/* mpi-gcd.c - MPI functions
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* Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
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*
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* This file is part of GnuPG.
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*
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* GnuPG 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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*
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* GnuPG 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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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include "mpi-internal.h"
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/****************
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* Find the greatest common divisor G of A and B.
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* Return: true if this 1, false in all other cases
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*/
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int mpi_gcd(MPI g, const MPI xa, const MPI xb)
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{
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MPI a = NULL, b = NULL;
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if (mpi_copy(&a, xa) < 0)
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goto nomem;
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if (mpi_copy(&b, xb) < 0)
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goto nomem;
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/* TAOCP Vol II, 4.5.2, Algorithm A */
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a->sign = 0;
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b->sign = 0;
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while (mpi_cmp_ui(b, 0)) {
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if (mpi_fdiv_r(g, a, b) < 0) /* g used as temorary variable */
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goto nomem;
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if (mpi_set(a, b) < 0)
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goto nomem;
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if (mpi_set(b, g) < 0)
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goto nomem;
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}
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if (mpi_set(g, a) < 0)
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goto nomem;
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mpi_free(a);
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mpi_free(b);
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return !mpi_cmp_ui(g, 1);
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nomem:
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mpi_free(a);
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mpi_free(b);
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return -ENOMEM;
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}
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