1 files changed, 74 insertions, 0 deletions
diff --git a/umac-poly64.c b/umac-poly64.c
new file mode 100644
index 00000000..bb4cb32c
--- /dev/null
+++ b/umac-poly64.c
@@ -0,0 +1,74 @@
+/* umac-poly64.c
+ */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2013 Niels Möller
+ *
+ * The nettle 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 2.1 of the License, or (at your
+ * option) any later version.
+ *
+ * The nettle 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 nettle library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+ * MA 02111-1301, USA.
+ */
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <assert.h>
+
+#include "umac.h"
+
+static uint64_t
+poly64_mul (uint32_t kh, uint32_t kl, uint64_t y)
+{
+  uint64_t yl, yh, pl, ph, ml, mh;
+  yl = y & 0xffffffff;
+  yh = y >> 32;
+  pl = yl * kl;
+  ph = yh * kh;
+  ml = yh * kl + yl * kh; /* No overflow, thanks to special form */
+  mh = ml >> 32;
+  ml <<= 32;
+  pl += ml;
+  ph += mh + (pl < ml);
+
+  /* Reduce, using 2^64 = UMAC_P64_OFFSET (mod p) */
+  assert (ph < ((uint64_t) 1 << 57));
+  ph *= UMAC_P64_OFFSET;
+  pl += ph;
+  if (pl < ph)
+    pl += UMAC_P64_OFFSET;
+
+  return pl;
+}
+
+uint64_t
+_umac_poly64 (uint32_t kh, uint32_t kl, uint64_t y, uint64_t m)
+{
+  if ( (m >> 32) == 0xffffffff)
+    {
+      y = poly64_mul (kh, kl, y);
+      if (y == 0)
+	y = UMAC_P64 - 1;
+      else
+	y--;
+      m -= UMAC_P64_OFFSET;
+    }
+  y = poly64_mul (kh, kl, y);
+  y += m;
+  if (y < m)
+    y += UMAC_P64_OFFSET;
+
+  return y;
+}