blockfilter: Use unordered_set instead of set in blockfilter.

src/Makefile.am

@@ -183,6 +183,7 @@ BITCOIN_CORE_H = \
   txmempool.h \
   ui_interface.h \
   undo.h \
+  util/bytevectorhash.h \
   util/system.h \
   util/memory.h \
   util/moneystr.h \
@@ -429,6 +430,7 @@ libbitcoin_util_a_SOURCES = \
   support/cleanse.cpp \
   sync.cpp \
   threadinterrupt.cpp \
+  util/bytevectorhash.cpp \
   util/system.cpp \
   util/moneystr.cpp \
   util/strencodings.cpp \

src/blockfilter.h

@@ -5,14 +5,15 @@
 #ifndef BITCOIN_BLOCKFILTER_H
 #define BITCOIN_BLOCKFILTER_H
 
-#include <set>
 #include <stdint.h>
+#include <unordered_set>
 #include <vector>
 
 #include <primitives/block.h>
 #include <serialize.h>
 #include <uint256.h>
 #include <undo.h>
+#include <util/bytevectorhash.h>
 
 /**
  * This implements a Golomb-coded set as defined in BIP 158. It is a
@@ -22,7 +23,7 @@ class GCSFilter
 {
 public:
     typedef std::vector<unsigned char> Element;
-    typedef std::set<Element> ElementSet;
+    typedef std::unordered_set<Element, ByteVectorHash> ElementSet;
 
 private:
     uint64_t m_siphash_k0;

src/util/bytevectorhash.cpp

@@ -0,0 +1,18 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <crypto/siphash.h>
+#include <random.h>
+#include <util/bytevectorhash.h>
+
+ByteVectorHash::ByteVectorHash()
+{
+    GetRandBytes(reinterpret_cast<unsigned char*>(&m_k0), sizeof(m_k0));
+    GetRandBytes(reinterpret_cast<unsigned char*>(&m_k1), sizeof(m_k1));
+}
+
+size_t ByteVectorHash::operator()(const std::vector<unsigned char>& input) const
+{
+    return CSipHasher(m_k0, m_k1).Write(input.data(), input.size()).Finalize();
+}

src/util/bytevectorhash.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_BYTEVECTORHASH_H
+#define BITCOIN_UTIL_BYTEVECTORHASH_H
+
+#include <stdint.h>
+#include <vector>
+
+/**
+ * Implementation of Hash named requirement for types that internally store a byte array. This may
+ * be used as the hash function in std::unordered_set or std::unordered_map over such types.
+ * Internally, this uses a random instance of SipHash-2-4.
+ */
+class ByteVectorHash final
+{
+private:
+    uint64_t m_k0, m_k1;
+
+public:
+    ByteVectorHash();
+    size_t operator()(const std::vector<unsigned char>& input) const;
+};
+
+#endif // BITCOIN_UTIL_BYTEVECTORHASH_H