From 5bfee602972cc30ef18cb22bfde560d60f5444e8 Mon Sep 17 00:00:00 2001
From: Anthony Fieroni <bvbfan@abv.bg>
Date: Fri, 20 Dec 2019 17:59:13 +0200
Subject: [PATCH] Use faster continuous memory hash computation

Signed-off-by: Anthony Fieroni <bvbfan@abv.bg>
---
 src/claimtrie/forks.cpp  | 5 +----
 src/claimtrie/hashes.cpp | 8 ++++++++
 src/claimtrie/hashes.h   | 5 +++++
 src/init.cpp             | 8 ++++++++
 4 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/src/claimtrie/forks.cpp b/src/claimtrie/forks.cpp
index 82fc18c17..dea3e7909 100644
--- a/src/claimtrie/forks.cpp
+++ b/src/claimtrie/forks.cpp
@@ -236,10 +236,7 @@ uint256 ComputeMerkleRoot(std::vector<uint256> hashes)
         if (hashes.size() & 1)
             hashes.push_back(hashes.back());
 
-        for (std::size_t i = 0, j = 0; i < hashes.size(); i += 2)
-            hashes[j++] = Hash(hashes[i].begin(), hashes[i].end(),
-                               hashes[i+1].begin(), hashes[i+1].end());
-
+        sha256n_way(hashes);
         hashes.resize(hashes.size() / 2);
     }
     return hashes.empty() ? uint256{} : hashes[0];
diff --git a/src/claimtrie/hashes.cpp b/src/claimtrie/hashes.cpp
index e0a2f293f..3be8f9b58 100644
--- a/src/claimtrie/hashes.cpp
+++ b/src/claimtrie/hashes.cpp
@@ -11,3 +11,11 @@ uint256 CalcHash(SHA256_CTX* sha)
     SHA256_Final(result.begin(), sha);
     return result;
 }
+
+// universal N way hash function
+std::function<void(std::vector<uint256>&)> sha256n_way =
+    [](std::vector<uint256>& hashes) {
+        for (std::size_t i = 0, j = 0; i < hashes.size(); i += 2)
+            hashes[j++] = Hash(hashes[i].begin(), hashes[i].end(),
+                               hashes[i+1].begin(), hashes[i+1].end());
+    };
diff --git a/src/claimtrie/hashes.h b/src/claimtrie/hashes.h
index 10709377d..9dadd5a73 100644
--- a/src/claimtrie/hashes.h
+++ b/src/claimtrie/hashes.h
@@ -4,6 +4,9 @@
 
 #include <openssl/sha.h>
 
+#include <functional>
+#include <vector>
+
 #include <uints.h>
 
 uint256 CalcHash(SHA256_CTX* sha);
@@ -25,4 +28,6 @@ uint256 Hash(TIterator begin, TIterator end, Args... args)
     return CalcHash(&sha, begin, end, args...);
 }
 
+extern std::function<void(std::vector<uint256>&)> sha256n_way;
+
 #endif // CLAIMTRIE_HASHES_H
diff --git a/src/init.cpp b/src/init.cpp
index 42996a3a1..bb0fc9967 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -15,6 +15,7 @@
 #include <chainparams.h>
 #include <checkpoints.h>
 #include <claimtrie/forks.h>
+#include <claimtrie/hashes.h>
 #include <clientversion.h>
 #include <compat/sanity.h>
 #include <consensus/validation.h>
@@ -1534,6 +1535,13 @@ bool AppInitMain()
                     assert(chainActive.Tip() != nullptr);
                 }
 
+                // use faster N way hash function
+                // NOTE: it assumes memory is continuous
+                // that means uint256 itself should use std::array or raw pointer
+                sha256n_way = [](std::vector<uint256>& hashes) {
+                    SHA256D64(hashes[0].begin(), hashes[0].begin(), hashes.size() / 2);
+                };
+
                 auto tip = chainActive.Tip();
                 if (tip && !CClaimTrieCache(pclaimTrie).validateDb(tip->nHeight, tip->hashClaimTrie)) {
                     strLoadError = _("Error validating the claim trie from disk");