Make difficulty 128 bit instead of 64 bit

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

1 files changed, 80 insertions, 3 deletions

diff --git a/src/cryptonote_basic/difficulty.cpp b/src/cryptonote_basic/difficulty.cpp
index 89b748a83..5162e53e6 100644
--- a/src/cryptonote_basic/difficulty.cpp
+++ b/src/cryptonote_basic/difficulty.cpp
@@ -102,7 +102,7 @@ namespace cryptonote {
     return a + b < a || (c && a + b == (uint64_t) -1);
   }
 
-  bool check_hash(const crypto::hash &hash, difficulty_type difficulty) {
+  bool check_hash_64(const crypto::hash &hash, uint64_t 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);
@@ -119,7 +119,7 @@ namespace cryptonote {
     return !carry;
   }
 
-  difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
+  uint64_t next_difficulty_64(std::vector<std::uint64_t> timestamps, std::vector<uint64_t> cumulative_difficulties, size_t target_seconds) {
 
     if(timestamps.size() > DIFFICULTY_WINDOW)
     {
@@ -150,7 +150,7 @@ namespace cryptonote {
     if (time_span == 0) {
       time_span = 1;
     }
-    difficulty_type total_work = cumulative_difficulties[cut_end - 1] - cumulative_difficulties[cut_begin];
+    uint64_t 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);
@@ -162,4 +162,81 @@ namespace cryptonote {
     return (low + time_span - 1) / time_span;
   }
 
+#if defined(_MSC_VER)
+#ifdef max
+#undef max
+#endif
+#endif
+
+  const difficulty_type max64bit(std::numeric_limits<std::uint64_t>::max());
+  const boost::multiprecision::uint256_t max128bit(std::numeric_limits<boost::multiprecision::uint128_t>::max());
+  const boost::multiprecision::uint512_t max256bit(std::numeric_limits<boost::multiprecision::uint256_t>::max());
+
+#define FORCE_FULL_128_BITS
+
+  bool check_hash_128(const crypto::hash &hash, difficulty_type difficulty) {
+#ifndef FORCE_FULL_128_BITS
+    // fast check
+    if (difficulty >= max64bit && ((const uint64_t *) &hash)[3] > 0)
+      return false;
+#endif
+    // usual slow check
+    boost::multiprecision::uint512_t hashVal = 0;
+#ifdef FORCE_FULL_128_BITS
+    for(int i = 0; i < 4; i++) { // highest word is zero
+#else
+    for(int i = 1; i < 4; i++) { // highest word is zero
+#endif
+      hashVal <<= 64;
+      hashVal |= swap64le(((const uint64_t *) &hash)[3 - i]);
+    }
+    return hashVal * difficulty <= max256bit;
+  }
+
+  bool check_hash(const crypto::hash &hash, difficulty_type difficulty) {
+    if (difficulty <= max64bit) // if can convert to small difficulty - do it
+      return check_hash_64(hash, difficulty.convert_to<std::uint64_t>());
+    else
+      return check_hash_128(hash, difficulty);
+  }
+
+  difficulty_type next_difficulty(std::vector<uint64_t> timestamps, std::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);
+    boost::multiprecision::uint256_t res =  (boost::multiprecision::uint256_t(total_work) * target_seconds + time_span - 1) / time_span;
+    if(res > max128bit)
+      return 0; // to behave like previous implementation, may be better return max128bit?
+    return res.convert_to<difficulty_type>();
+  }
+
 }