Make difficulty 128 bit instead of 64 bit

Based on Boolberry work by:
  jahrsg <jahr@jahr.me>
  cr.zoidberg <crypto.zoidberg@gmail.com>

tests/unit_tests/CMakeLists.txt

@@ -43,6 +43,7 @@ set(unit_tests_sources
   crypto.cpp
   decompose_amount_into_digits.cpp
   device.cpp
+  difficulty.cpp
   dns_resolver.cpp
   epee_boosted_tcp_server.cpp
   epee_levin_protocol_handler_async.cpp

tests/unit_tests/difficulty.cpp

@@ -0,0 +1,68 @@
+// Copyright (c) 2019, The Monero Project
+// 
+// All rights reserved.
+// 
+// Redistribution and use in source and binary forms, with or without modification, are
+// permitted provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list
+//    of conditions and the following disclaimer in the documentation and/or other
+//    materials provided with the distribution.
+// 
+// 3. Neither the name of the copyright holder nor the names of its contributors may be
+//    used to endorse or promote products derived from this software without specific
+//    prior written permission.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
+// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
+// THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+// STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "gtest/gtest.h"
+#include "cryptonote_basic/difficulty.h"
+
+static cryptonote::difficulty_type MKDIFF(uint64_t high, uint64_t low)
+{
+  cryptonote::difficulty_type d = high;
+  d = (d << 64) | low;
+  return d;
+}
+
+static crypto::hash MKHASH(uint64_t high, uint64_t low)
+{
+  cryptonote::difficulty_type hash_target = high;
+  hash_target = (hash_target << 64) | low;
+  boost::multiprecision::uint256_t hash_value = std::numeric_limits<boost::multiprecision::uint256_t>::max() / hash_target;
+  crypto::hash h;
+  ((uint64_t*)&h)[0] = hash_value.convert_to<uint64_t>();
+  hash_value >>= 64;
+  ((uint64_t*)&h)[1] = hash_value.convert_to<uint64_t>();
+  hash_value >>= 64;
+  ((uint64_t*)&h)[2] = hash_value.convert_to<uint64_t>();
+  hash_value >>= 64;
+  ((uint64_t*)&h)[3] = hash_value.convert_to<uint64_t>();
+  return h;
+}
+
+TEST(difficulty, check_hash)
+{
+  ASSERT_TRUE(cryptonote::check_hash(MKHASH(0, 1), MKDIFF(0, 1)));
+  ASSERT_FALSE(cryptonote::check_hash(MKHASH(0, 1), MKDIFF(0, 2)));
+
+  ASSERT_TRUE(cryptonote::check_hash(MKHASH(0, 0xffffffffffffffff), MKDIFF(0, 0xffffffffffffffff)));
+  ASSERT_FALSE(cryptonote::check_hash(MKHASH(0, 0xffffffffffffffff), MKDIFF(1, 0)));
+
+  ASSERT_TRUE(cryptonote::check_hash(MKHASH(1, 1), MKDIFF(1, 1)));
+  ASSERT_FALSE(cryptonote::check_hash(MKHASH(1, 1), MKDIFF(1, 2)));
+
+  ASSERT_TRUE(cryptonote::check_hash(MKHASH(0xffffffffffffffff, 1), MKDIFF(0xffffffffffffffff, 1)));
+  ASSERT_FALSE(cryptonote::check_hash(MKHASH(0xffffffffffffffff, 1), MKDIFF(0xffffffffffffffff, 2)));
+}

tests/unit_tests/serialization.cpp

@@ -1187,3 +1187,26 @@ TEST(Serialization, portability_signed_tx)
   ASSERT_TRUE(epee::string_tools::pod_to_hex(ki1) == "d54cbd435a8d636ad9b01b8d4f3eb13bd0cf1ce98eddf53ab1617f9b763e66c0");
   ASSERT_TRUE(epee::string_tools::pod_to_hex(ki2) == "6c3cd6af97c4070a7aef9b1344e7463e29c7cd245076fdb65da447a34da3ca76");
 }
+
+TEST(Serialization, difficulty_type)
+{
+  std::vector<cryptonote::difficulty_type> v_original;
+
+  for(int i = 0; i != 100; i++)
+  {
+    v_original.push_back(cryptonote::difficulty_type("117868131154734361989189100"));
+    if(v_original.size() > 1)
+      v_original.back() *= v_original[v_original.size()-2];
+  }
+
+  std::stringstream ss;
+  boost::archive::portable_binary_oarchive a(ss);
+  a << v_original;
+
+  std::vector<cryptonote::difficulty_type> v_unserialized;
+
+  boost::archive::portable_binary_iarchive a2(ss);
+  a2 >> v_unserialized;
+
+  ASSERT_EQ(v_original, v_unserialized);
+}