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diff --git a/src/mongo/db/ops/modifier_compare.h b/src/mongo/db/ops/modifier_compare.h
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+++ b/src/mongo/db/ops/modifier_compare.h
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+/**
+ *    Copyright (C) 2013 10gen Inc.
+ *
+ *    This program is free software: you can redistribute it and/or  modify
+ *    it under the terms of the GNU Affero General Public License, version 3,
+ *    as published by the Free Software Foundation.
+ *
+ *    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 Affero General Public License for more details.
+ *
+ *    You should have received a copy of the GNU Affero General Public License
+ *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <boost/scoped_ptr.hpp>
+#include <string>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/bson/mutable/element.h"
+#include "mongo/db/field_ref.h"
+#include "mongo/db/jsobj.h"
+#include "mongo/db/ops/modifier_interface.h"
+
+namespace mongo {
+
+    class LogBuilder;
+
+    class ModifierCompare : public ModifierInterface {
+        MONGO_DISALLOW_COPYING(ModifierCompare);
+
+    public:
+
+        enum ModifierCompareMode { MAX, MIN };
+        explicit ModifierCompare(ModifierCompareMode mode = MAX);
+
+        virtual ~ModifierCompare();
+
+        //
+        // Modifier interface implementation
+        //
+
+        /**
+         * A 'modExpr' is a BSONElement {<fieldname>: <value>} coming from a $set mod such as
+         * {$set: {<fieldname: <value>}}. init() extracts the field name and the value to be
+         * assigned to it from 'modExpr'. It returns OK if successful or a status describing
+         * the error.
+         */
+        virtual Status init(const BSONElement& modExpr, const Options& opts);
+
+        /**
+         * Looks up the field name in the sub-tree rooted at 'root', and binds, if necessary,
+         * the '$' field part using the 'matchedfield' number. prepare() returns OK and
+         * fills in 'execInfo' with information of whether this mod is a no-op on 'root' and
+         * whether it is an in-place candidate. Otherwise, returns a status describing the
+         * error.
+         */
+        virtual Status prepare(mutablebson::Element root,
+                               const StringData& matchedField,
+                               ExecInfo* execInfo);
+
+        /**
+         * Applies the prepared mod over the element 'root' specified in the prepare()
+         * call. Returns OK if successful or a status describing the error.
+         */
+        virtual Status apply() const;
+
+        /**
+         * Adds a log entry to logRoot corresponding to the operation applied here. Returns OK
+         * if successful or a status describing the error.
+         */
+        virtual Status log(LogBuilder* logBuilder) const;
+
+    private:
+
+        // Compare mode: min/max
+        const ModifierCompareMode _mode;
+
+        // Access to each component of fieldName that's the target of this mod.
+        FieldRef _updatePath;
+
+        // 0 or index for $-positional in _updatePath.
+        size_t _pathReplacementPosition;
+
+        // Element of the mod expression.
+        BSONElement _val;
+
+        // The instance of the field in the provided doc. This state is valid after a
+        // prepare() was issued and until a log() is issued. The document this mod is
+        // being prepared against must be live throughout all the calls.
+        struct PreparedState;
+        scoped_ptr<PreparedState> _preparedState;
+    };
+
+} // namespace mongo