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-rw-r--r--lib/mpi/mpi-gcd.c59
1 files changed, 59 insertions, 0 deletions
diff --git a/lib/mpi/mpi-gcd.c b/lib/mpi/mpi-gcd.c
new file mode 100644
index 000000000000..13c48aef9c4e
--- /dev/null
+++ b/lib/mpi/mpi-gcd.c
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+/* mpi-gcd.c - MPI functions
+ * Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
+ *
+ * This file is part of GnuPG.
+ *
+ * GnuPG 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.
+ *
+ * GnuPG 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
+ */
+
+#include "mpi-internal.h"
+
+/****************
+ * Find the greatest common divisor G of A and B.
+ * Return: true if this 1, false in all other cases
+ */
+int mpi_gcd(MPI g, const MPI xa, const MPI xb)
+{
+ MPI a = NULL, b = NULL;
+
+ if (mpi_copy(&a, xa) < 0)
+ goto nomem;
+
+ if (mpi_copy(&b, xb) < 0)
+ goto nomem;
+
+ /* TAOCP Vol II, 4.5.2, Algorithm A */
+ a->sign = 0;
+ b->sign = 0;
+ while (mpi_cmp_ui(b, 0)) {
+ if (mpi_fdiv_r(g, a, b) < 0) /* g used as temorary variable */
+ goto nomem;
+ if (mpi_set(a, b) < 0)
+ goto nomem;
+ if (mpi_set(b, g) < 0)
+ goto nomem;
+ }
+ if (mpi_set(g, a) < 0)
+ goto nomem;
+
+ mpi_free(a);
+ mpi_free(b);
+ return !mpi_cmp_ui(g, 1);
+
+nomem:
+ mpi_free(a);
+ mpi_free(b);
+ return -ENOMEM;
+}