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diff --git a/src/mongo/bson/util/simple8b.cpp b/src/mongo/bson/util/simple8b.cpp
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+++ b/src/mongo/bson/util/simple8b.cpp
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+/**
+ *    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.
+ */
+
+#include "mongo/bson/util/simple8b.h"
+
+namespace mongo {
+
+namespace {
+static constexpr uint8_t _maxSelector = 15;
+static constexpr uint8_t _minSelector = 2;
+static constexpr uint64_t _selectorMask = 0xF000000000000000;
+static constexpr uint8_t _selectorSize = 4;
+static constexpr uint8_t _dataSize = 60;
+
+// Pass the selector as the index to get the corresponding mask.
+// Get the maskSize by getting the number of bits for the selector. Then 2^maskSize - 1.
+const uint64_t _selectorForMask[16] = {0, 0, 1, 3, 7, 15, 31, 63, 127, 255, 1023, 4095, 32767, 1048575, 1073741823, 1152921504606846975};
+
+
+// Pass the selector value as the index to get the number of bits per integer in the Simple8b block.
+const uint8_t _selectorForBitsPerInteger[16] = {0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 15, 20, 30, 60};
+
+// Pass the selector value as the index to get the number of integers coded in the Simple8b block.
+const uint8_t _selectorForIntegersCoded[16] = {240, 120, 60, 30, 20, 15, 12, 10, 8, 7, 6, 5, 4, 3, 2, 1};
+
+}
+
+uint64_t Simple8b::encodeSimple8b(uint8_t selector, const std::vector<uint64_t>& values) {
+    if (selector > _maxSelector || selector < _minSelector)
+        return errCode;
+
+    uint8_t bitsPerInteger = _selectorForBitsPerInteger[selector];
+    uint8_t integersCoded = _selectorForIntegersCoded[selector];
+
+    uint64_t encodedWord = (uint64_t) selector << _dataSize;
+
+    for (uint8_t i = 0; i < integersCoded; ++i) {
+        uint8_t shiftSize = _dataSize - bitsPerInteger * (i + 1);
+        encodedWord += values[i] << shiftSize;
+    }
+
+    return encodedWord;
+}
+
+ 
+std::vector<uint64_t> Simple8b::decodeSimple8b(const uint64_t simple8bWord) {
+    std::vector<uint64_t> values;
+
+    uint8_t selector = (simple8bWord & _selectorMask) >> _dataSize;
+
+    if (selector < _minSelector)
+        return values;
+
+    uint8_t bitsPerInteger = _selectorForBitsPerInteger[selector];
+    uint8_t integersCoded = _selectorForIntegersCoded[selector];
+
+    for (int8_t i = integersCoded - 1; i >= 0; --i) {
+        uint8_t startIdx = bitsPerInteger * i;
+
+        uint64_t mask = _selectorForMask[selector] << startIdx; 
+        uint64_t value = (simple8bWord & mask) >> startIdx;
+
+        values.push_back(value);
+    }
+
+    return values; 
+}
+
+} // namespace mongo