Add function mpz_powm_sec.

1 files changed, 90 insertions, 0 deletions

diff --git a/mpz/powm_sec.c b/mpz/powm_sec.c
new file mode 100644
index 000000000..2432fe498
--- /dev/null
+++ b/mpz/powm_sec.c
@@ -0,0 +1,90 @@
+/* mpz_powm_sec(res,base,exp,mod) -- Set R to (U^E) mod M.
+
+   Contributed to the GNU project by Torbjorn Granlund.
+
+Copyright 1991, 1993, 1994, 1996, 1997, 2000, 2001, 2002, 2005, 2008, 2009
+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"
+
+
+void
+mpz_powm_sec (mpz_ptr r, mpz_srcptr b, mpz_srcptr e, mpz_srcptr m)
+{
+  mp_size_t n;
+  mp_ptr rp, tp;
+  mp_srcptr bp, ep, mp;
+  mp_size_t rn, bn, es, en;
+  TMP_DECL;
+
+  n = ABSIZ(m);
+  if (n == 0)
+    DIVIDE_BY_ZERO;
+
+  mp = PTR(m);
+
+  if (mp[0] % 2 == 0)
+    DIVIDE_BY_ZERO;
+
+  es = SIZ(e);
+  if (UNLIKELY (es <= 0))
+    {
+      mpz_t new_b;
+      if (es == 0)
+	{
+	  /* b^0 mod m,  b is anything and m is non-zero.
+	     Result is 1 mod m, i.e., 1 or 0 depending on if m = 1.  */
+	  SIZ(r) = n != 1 || mp[0] != 1;
+	  PTR(r)[0] = 1;
+	  return;
+	}
+      DIVIDE_BY_ZERO;
+    }
+
+  en = es;
+  bn = ABSIZ(b);
+
+  TMP_MARK;
+  tp = TMP_ALLOC_LIMBS (n + mpn_powm_sec_itch (bn, en, n));
+
+  rp = tp;  tp += n;
+
+  bp = PTR(b);
+  ep = PTR(e);
+
+  mpn_powm_sec (rp, bp, bn, ep, en, mp, n, tp);
+
+  rn = n;
+
+  MPN_NORMALIZE (rp, rn);
+
+  if ((ep[0] & 1) && SIZ(b) < 0 && rn != 0)
+    {
+      mpn_sub (rp, PTR(m), n, rp, rn);
+      rn = n;
+      MPN_NORMALIZE (rp, rn);
+    }
+
+  MPZ_REALLOC (r, rn);
+  SIZ(r) = rn;
+  MPN_COPY (PTR(r), rp, rn);
+
+  TMP_FREE;
+}