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 000000000000..ffa328818ca6
--- /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;
+}