1 files changed, 111 insertions, 0 deletions
diff --git a/src/cryptonote_core/difficulty.cpp b/src/cryptonote_core/difficulty.cpp
new file mode 100644
index 000000000..052f46662
--- /dev/null
+++ b/src/cryptonote_core/difficulty.cpp
@@ -0,0 +1,111 @@
+// Copyright (c) 2012-2013 The Cryptonote developers
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <vector>
+
+#include "common/int-util.h"
+#include "crypto/hash.h"
+#include "cryptonote_config.h"
+#include "difficulty.h"
+
+namespace cryptonote {
+
+  using std::size_t;
+  using std::uint64_t;
+  using std::vector;
+
+#if defined(_MSC_VER)
+#include <windows.h>
+#include <winnt.h>
+
+  static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
+    low = UnsignedMultiply128(a, b, &high);
+  }
+
+#else
+
+  static inline void mul(uint64_t a, uint64_t b, uint64_t &low, uint64_t &high) {
+    typedef unsigned __int128 uint128_t;
+    uint128_t res = (uint128_t) a * (uint128_t) b;
+    low = (uint64_t) res;
+    high = (uint64_t) (res >> 64);
+  }
+
+#endif
+
+  static inline bool cadd(uint64_t a, uint64_t b) {
+    return a + b < a;
+  }
+
+  static inline bool cadc(uint64_t a, uint64_t b, bool c) {
+    return a + b < a || (c && a + b == (uint64_t) -1);
+  }
+
+  bool check_hash(const crypto::hash &hash, difficulty_type difficulty) {
+    uint64_t low, high, top, cur;
+    // First check the highest word, this will most likely fail for a random hash.
+    mul(swap64le(((const uint64_t *) &hash)[3]), difficulty, top, high);
+    if (high != 0) {
+      return false;
+    }
+    mul(swap64le(((const uint64_t *) &hash)[0]), difficulty, low, cur);
+    mul(swap64le(((const uint64_t *) &hash)[1]), difficulty, low, high);
+    bool carry = cadd(cur, low);
+    cur = high;
+    mul(swap64le(((const uint64_t *) &hash)[2]), difficulty, low, high);
+    carry = cadc(cur, low, carry);
+    carry = cadc(high, top, carry);
+    return !carry;
+  }
+
+  difficulty_type next_difficulty(vector<uint64_t> timestamps, vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
+    //cutoff DIFFICULTY_LAG
+    if(timestamps.size() > DIFFICULTY_WINDOW)
+    {
+      timestamps.resize(DIFFICULTY_WINDOW);
+      cumulative_difficulties.resize(DIFFICULTY_WINDOW);
+    }
+
+
+    size_t length = timestamps.size();
+    assert(length == cumulative_difficulties.size());
+    if (length <= 1) {
+      return 1;
+    }
+    static_assert(DIFFICULTY_WINDOW >= 2, "Window is too small");
+    assert(length <= DIFFICULTY_WINDOW);
+    sort(timestamps.begin(), timestamps.end());
+    size_t cut_begin, cut_end;
+    static_assert(2 * DIFFICULTY_CUT <= DIFFICULTY_WINDOW - 2, "Cut length is too large");
+    if (length <= DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) {
+      cut_begin = 0;
+      cut_end = length;
+    } else {
+      cut_begin = (length - (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT) + 1) / 2;
+      cut_end = cut_begin + (DIFFICULTY_WINDOW - 2 * DIFFICULTY_CUT);
+    }
+    assert(/*cut_begin >= 0 &&*/ cut_begin + 2 <= cut_end && cut_end <= length);
+    uint64_t time_span = timestamps[cut_end - 1] - timestamps[cut_begin];
+    if (time_span == 0) {
+      time_span = 1;
+    }
+    difficulty_type total_work = cumulative_difficulties[cut_end - 1] - cumulative_difficulties[cut_begin];
+    assert(total_work > 0);
+    uint64_t low, high;
+    mul(total_work, target_seconds, low, high);
+    if (high != 0 || low + time_span - 1 < low) {
+      return 0;
+    }
+    return (low + time_span - 1) / time_span;
+  }
+
+  difficulty_type next_difficulty(vector<uint64_t> timestamps, vector<difficulty_type> cumulative_difficulties)
+  {
+    return next_difficulty(std::move(timestamps), std::move(cumulative_difficulties), DIFFICULTY_TARGET);
+  }
+}