1 files changed, 63 insertions, 0 deletions
diff --git a/lib/mpi/generic_mpih-rshift.c b/lib/mpi/generic_mpih-rshift.c
new file mode 100644
index 000000000..ffa328818
--- /dev/null
+++ b/lib/mpi/generic_mpih-rshift.c
@@ -0,0 +1,63 @@
+/* mpih-rshift.c  -  MPI helper functions
+ * Copyright (C) 1994, 1996, 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
+ *
+ * Note: This code is heavily based on the GNU MP Library.
+ *	 Actually it's the same code with only minor changes in the
+ *	 way the data is stored; this is to support the abstraction
+ *	 of an optional secure memory allocation which may be used
+ *	 to avoid revealing of sensitive data due to paging etc.
+ *	 The GNU MP Library itself is published under the LGPL;
+ *	 however I decided to publish this code under the plain GPL.
+ */
+
+#include "mpi-internal.h"
+
+/* Shift U (pointed to by UP and USIZE limbs long) CNT bits to the right
+ * and store the USIZE least significant limbs of the result at WP.
+ * The bits shifted out to the right are returned.
+ *
+ * Argument constraints:
+ * 1. 0 < CNT < BITS_PER_MP_LIMB
+ * 2. If the result is to be written over the input, WP must be <= UP.
+ */
+
+mpi_limb_t
+mpihelp_rshift(mpi_ptr_t wp, mpi_ptr_t up, mpi_size_t usize, unsigned cnt)
+{
+	mpi_limb_t high_limb, low_limb;
+	unsigned sh_1, sh_2;
+	mpi_size_t i;
+	mpi_limb_t retval;
+
+	sh_1 = cnt;
+	wp -= 1;
+	sh_2 = BITS_PER_MPI_LIMB - sh_1;
+	high_limb = up[0];
+	retval = high_limb << sh_2;
+	low_limb = high_limb;
+	for (i = 1; i < usize; i++) {
+		high_limb = up[i];
+		wp[i] = (low_limb >> sh_1) | (high_limb << sh_2);
+		low_limb = high_limb;
+	}
+	wp[i] = low_limb >> sh_1;
+
+	return retval;
+}