Split ecc_generic_redc into two functions ecc_pp1_redc and ecc_pm1_redc.

1 files changed, 71 insertions, 0 deletions

diff --git a/ecc-pp1-redc.c b/ecc-pp1-redc.c
new file mode 100644
index 00000000..e2216119
--- /dev/null
+++ b/ecc-pp1-redc.c
@@ -0,0 +1,71 @@
+/* ecc-pp1-redc.c
+
+   Copyright (C) 2013, 2014 Niels Möller
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * 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.
+
+   or
+
+     * 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.
+
+   or both in parallel, as here.
+
+   GNU Nettle 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 copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+
+/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <assert.h>
+
+#include "ecc-internal.h"
+
+/* Use that 1 = p + 1 (mod p), and that at least one low limb of p + 1
+   is zero. */
+void
+ecc_pp1_redc (const struct ecc_curve *ecc, mp_limb_t *rp)
+{
+  unsigned i;
+  mp_limb_t hi, cy;
+  unsigned shift = ecc->size * GMP_NUMB_BITS - ecc->bit_size;
+  mp_size_t k = ecc->redc_size;
+  
+  assert (k > 0);
+
+  for (i = 0; i < ecc->size; i++)
+    rp[i] = mpn_addmul_1 (rp + i + k,
+			  ecc->redc_ppm1, ecc->size - k, rp[i]);
+  hi = mpn_add_n (rp, rp, rp + ecc->size, ecc->size);
+  if (shift > 0)
+    {
+      hi = (hi << shift) | (rp[ecc->size - 1] >> (GMP_NUMB_BITS - shift));
+      rp[ecc->size - 1] = (rp[ecc->size - 1]
+			   & (((mp_limb_t) 1 << (GMP_NUMB_BITS - shift)) - 1))
+	+ mpn_addmul_1 (rp, ecc->Bmodp_shifted, ecc->size-1, hi);
+	  
+    }
+  else
+    {
+      cy = cnd_sub_n (hi, rp, ecc->p, ecc->size);
+      assert (cy == hi);      
+    }
+}