use sha256 based splittable rng

lib/lattice/rng/sprng-sha256.h

@@ -0,0 +1,109 @@
+// vim: set ts=2 sw=2 expandtab:
+
+// Copyright (c) 2016 Luchang Jin
+// All rights reserved.
+
+// This program 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 3 of the License, or
+// (at your option) any later version.
+//
+// This program 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, see <http://www.gnu.org/licenses/>.
+
+#pragma once
+
+#include "rng-state.h"
+
+#include <array>
+#include <cstring>
+#include <ostream>
+#include <istream>
+
+#ifdef CURRENT_DEFAULT_NAMESPACE_NAME
+namespace CURRENT_DEFAULT_NAMESPACE_NAME {
+#endif
+
+struct SprngSha256
+{
+  RngState rs;
+  //
+  using result_type = uint64_t;
+  //
+  static constexpr result_type default_seed = 0;
+  //
+  explicit SprngSha256(result_type val = default_seed)
+  {
+    seed(val);
+  }
+  template<typename Sseq, typename = typename
+    std::enable_if<!std::is_same<Sseq, SprngSha256>::value>
+    ::type>
+  explicit SprngSha256(Sseq& q)
+  {
+    seed(q);
+  }
+  //
+  static constexpr result_type min()
+  {
+    return 0;
+  }
+  //
+  static constexpr result_type max()
+  {
+    return UINT64_MAX;
+  }
+  //
+  void seed(result_type val = default_seed)
+  {
+    reset(rs, (long)val);
+  }
+  template <class Sseq>
+  typename std::enable_if<std::is_class<Sseq>::value>::type
+  seed(Sseq& q)
+  {
+    std::array<uint32_t, 8> seq;
+    q.generate(seq.begin(), seq.end());
+    for (size_t i = 0; i < seq.size(); ++i) {
+      splitRngState(rs, rs, seq[i]);
+    }
+  }
+  //
+  result_type operator()()
+  {
+    return randGen(rs);
+  }
+  //
+  void discard(unsigned long long z)
+  {
+    for (unsigned long long i = 0; i < z; ++i) {
+      randGen(rs);
+    }
+  }
+};
+
+inline std::ostream& operator<<(std::ostream& os, const SprngSha256& ss)
+{
+  os << ss.rs;
+  return os;
+}
+
+inline std::istream& operator>>(std::istream& is, SprngSha256& ss)
+{
+  is >> ss.rs;
+  return is;
+}
+
+inline bool operator==(const SprngSha256& ss1, const SprngSha256& ss2)
+{
+  return ss1.rs == ss2.rs;
+}
+
+#ifdef CURRENT_DEFAULT_NAMESPACE_NAME
+}
+#endif