diff --git a/src/cryptonote_core/difficulty.cpp b/src/cryptonote_core/difficulty.cpp
index 236e84481..54da77392 100644
--- a/src/cryptonote_core/difficulty.cpp
+++ b/src/cryptonote_core/difficulty.cpp
@@ -116,8 +116,8 @@ namespace cryptonote {
     return !carry;
   }
 
-  difficulty_type next_difficulty(vector<uint64_t> timestamps, vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
-    //cutoff DIFFICULTY_LAG
+  difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds) {
+
     if(timestamps.size() > DIFFICULTY_WINDOW)
     {
       timestamps.resize(DIFFICULTY_WINDOW);
@@ -151,6 +151,8 @@ namespace cryptonote {
     assert(total_work > 0);
     uint64_t low, high;
     mul(total_work, target_seconds, low, high);
+    // blockchain errors "difficulty overhead" if this function returns zero.
+    // TODO: consider throwing an exception instead
     if (high != 0 || low + time_span - 1 < low) {
       return 0;
     }
diff --git a/src/cryptonote_core/difficulty.h b/src/cryptonote_core/difficulty.h
index d49c2f3b8..910f97035 100644
--- a/src/cryptonote_core/difficulty.h
+++ b/src/cryptonote_core/difficulty.h
@@ -39,6 +39,18 @@ namespace cryptonote
 {
     typedef std::uint64_t difficulty_type;
 
+    /**
+     * @brief checks if a hash fits the given difficulty
+     *
+     * The hash passes if (hash * difficulty) < 2^192.
+     * Phrased differently, if (hash * difficulty) fits without overflow into
+     * the least significant 192 bits of the 256 bit multiplication result.
+     *
+     * @param hash the hash to check
+     * @param difficulty the difficulty to check against
+     *
+     * @return true if valid, else false
+     */
     bool check_hash(const crypto::hash &hash, difficulty_type difficulty);
     difficulty_type next_difficulty(std::vector<std::uint64_t> timestamps, std::vector<difficulty_type> cumulative_difficulties, size_t target_seconds);
 }