Merge pull request #2004 from drrtuy/MCOL-4759

MCOL-4759 Upmerge for MCOL-4564 code that implements hash merging fam…

utils/common/hashfamily.h

@@ -0,0 +1,57 @@
+/* Copyright (C) 2021 Mariadb Corporation.
+
+   This program is free software; you can redistribute it and/or
+   modify it under the terms of the GNU General Public License
+   as published by the Free Software Foundation; version 2 of
+   the License.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+   MA 02110-1301, USA. */
+
+#ifndef UTILS_HASHFAMILY_H
+#define UTILS_HASHFAMILY_H
+
+#include "hasher.h"
+#include "collation.h"
+
+namespace utils
+{
+
+class HashFamily
+{
+  public:
+    HashFamily(const utils::Hasher_r& h,
+               const uint64_t intermediateHash,
+               const uint64_t len,
+               const datatypes::MariaDBHasher& hM) : mHasher(h),
+                                                     mMariaDBHasher(hM),
+                                                     mHasher_rHash(intermediateHash),
+                                                     mHasher_rLen(len)
+    { }
+
+    // Algorithm, seed and factor are taken from this discussion
+    // https://stackoverflow.com/questions/1646807/quick-and-simple-hash-code-combinations
+    inline uint64_t finalize() const
+    {
+      return (seed * factor + mHasher.finalize(mHasher_rHash, mHasher_rLen)) * factor + mMariaDBHasher.finalize();
+    }
+  private:
+    constexpr static uint64_t seed = 1009ULL;
+    constexpr static uint64_t factor = 9176ULL;
+
+    const utils::Hasher_r& mHasher;
+    const datatypes::MariaDBHasher& mMariaDBHasher;
+    const uint64_t mHasher_rHash;
+    const uint32_t mHasher_rLen;
+};
+
+}
+#endif
+// vim:ts=2 sw=2: