1 files changed, 48 insertions, 0 deletions
diff --git a/mpn/generic/tabselect.c b/mpn/generic/tabselect.c
new file mode 100644
index 000000000..02e52fdc0
--- /dev/null
+++ b/mpn/generic/tabselect.c
@@ -0,0 +1,48 @@
+/* mpn_tabselect.
+
+   THIS IS AN INTERNAL FUNCTION WITH A MUTABLE INTERFACE.  IT IS ONLY
+   SAFE TO REACH THIS FUNCTION THROUGH DOCUMENTED INTERFACES.
+
+Copyright 2007, 2008, 2009, 2011 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 3 of the License, or (at your
+option) any later version.
+
+The GNU MP Library 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 Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+
+/* Select entry `which' from table `tab', which has nents entries, each `n'
+   limbs.  Store the selected entry at rp.  Reads entire table to avoid
+   side-channel information leaks.  O(n*nents).
+   FIXME: Move to its own file.  */
+void
+mpn_tabselect (volatile mp_limb_t *rp, volatile mp_limb_t *tab, mp_size_t n,
+	       mp_size_t nents, mp_size_t which)
+{
+  mp_size_t k, i;
+  mp_limb_t mask;
+  volatile mp_limb_t *tp;
+
+  for (k = 0; k < nents; k++)
+    {
+      mask = -(mp_limb_t) (which == k);
+      tp = tab + n * k;
+      for (i = 0; i < n; i++)
+	{
+	  rp[i] = (rp[i] & ~mask) | (tp[i] & mask);
+	}
+    }
+}