Implement index-truncation Equihash optimisation

src/crypto/equihash.h

@@ -17,6 +17,7 @@
 
 typedef crypto_generichash_blake2b_state eh_HashState;
 typedef uint32_t eh_index;
+typedef uint8_t eh_trunc;
 
 struct invalid_params { };
 
@@ -66,9 +67,33 @@ public:
     }
 
     friend bool DistinctIndices(const FullStepRow& a, const FullStepRow& b);
+    friend bool IsValidBranch(const FullStepRow& a, const unsigned int ilen, const eh_trunc t);
 };
 
 bool DistinctIndices(const FullStepRow& a, const FullStepRow& b);
+bool IsValidBranch(const FullStepRow& a, const unsigned int ilen, const eh_trunc t);
+
+class TruncatedStepRow : public StepRow
+{
+private:
+    std::vector<eh_trunc> indices;
+
+public:
+    TruncatedStepRow(unsigned int n, const eh_HashState& base_state, eh_index i, unsigned int ilen);
+    ~TruncatedStepRow() { }
+
+    TruncatedStepRow(const TruncatedStepRow& a) : StepRow {a}, indices(a.indices) { }
+    TruncatedStepRow& operator=(const TruncatedStepRow& a);
+    TruncatedStepRow& operator^=(const TruncatedStepRow& a);
+
+    bool IndicesBefore(const TruncatedStepRow& a) { return indices[0] < a.indices[0]; }
+    std::vector<eh_trunc> GetPartialSolution() { return std::vector<eh_trunc>(indices); }
+
+    friend inline const TruncatedStepRow operator^(const TruncatedStepRow& a, const TruncatedStepRow& b) {
+        if (a.indices[0] < b.indices[0]) { return TruncatedStepRow(a) ^= b; }
+        else { return TruncatedStepRow(b) ^= a; }
+    }
+};
 
 class Equihash
 {
@@ -84,6 +109,7 @@ public:
 
     int InitialiseState(eh_HashState& base_state);
     std::set<std::vector<eh_index>> BasicSolve(const eh_HashState& base_state);
+    std::set<std::vector<eh_index>> OptimisedSolve(const eh_HashState& base_state);
     bool IsValidSolution(const eh_HashState& base_state, std::vector<eh_index> soln);
 };