1 files changed, 64 insertions, 0 deletions
diff --git a/src/mongo/bson/util/simple8b.h b/src/mongo/bson/util/simple8b.h
new file mode 100644
index 00000000000..2c6e4207698
--- /dev/null
+++ b/src/mongo/bson/util/simple8b.h
@@ -0,0 +1,64 @@
+/**
+ *    Copyright (C) 2021-present MongoDB, Inc.
+ *
+ *    This program is free software: you can redistribute it and/or modify
+ *    it under the terms of the Server Side Public License, version 1,
+ *    as published by MongoDB, Inc.
+ *
+ *    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
+ *    Server Side Public License for more details.
+ *
+ *    You should have received a copy of the Server Side Public License
+ *    along with this program. If not, see
+ *    <http://www.mongodb.com/licensing/server-side-public-license>.
+ *
+ *    As a special exception, the copyright holders give permission to link the
+ *    code of portions of this program with the OpenSSL library under certain
+ *    conditions as described in each individual source file and distribute
+ *    linked combinations including the program with the OpenSSL library. You
+ *    must comply with the Server Side Public License in all respects for
+ *    all of the code used other than as permitted herein. If you modify file(s)
+ *    with this exception, you may extend this exception to your version of the
+ *    file(s), but you are not obligated to do so. If you do not wish to do so,
+ *    delete this exception statement from your version. If you delete this
+ *    exception statement from all source files in the program, then also delete
+ *    it in the license file.
+ */
+
+#pragma once
+
+#include <cmath>
+#include <iostream>
+#include <vector>
+
+
+namespace mongo {
+
+/**
+ * As of now, Simple8b is a static class that can encode a series of integers and a selector value
+ * into a single 64 bit Simple8b word.
+ */
+class Simple8b {
+public:
+    // A valid Simple8b should never have a selector value of 1, so we will use it as an error code.
+    static const uint64_t errCode = 0x1000000000000000;
+
+    /**
+     * encodeSimple8b takes a selector and a vector of integers to be compressed into a 64 bit word.
+     * If there are wasted bits, it will be at the very right side.
+     * For now, we will assume that all ints in the vector are greater or equal to zero.
+     * We will also assume that the selector and all values will fit into the 64 bit word.
+     * Returns the encoded Simple8b word if the inputs are valid and errCode otherwise.
+     */
+    static uint64_t encodeSimple8b(uint8_t selector, const std::vector<uint64_t>& values);
+    
+    /**
+     * decodeSimple8b decodes a simple8b word into a vector of integers.
+     * Only when the selector is invalid will the returned vector be empty.
+     */
+    static std::vector<uint64_t> decodeSimple8b(uint64_t simple8bWord);
+};
+
+} // namespace mongo