SERVER-21481 optimize generating indices in BSONArrayBuilder

1 files changed, 57 insertions, 0 deletions

diff --git a/src/mongo/util/itoa.h b/src/mongo/util/itoa.h
new file mode 100644
index 00000000000..7d02f82400c
--- /dev/null
+++ b/src/mongo/util/itoa.h
@@ -0,0 +1,57 @@
+/**
+ *    Copyright (C) 2015 MongoDB 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/>.
+ *
+ *    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 GNU Affero General 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 <cstdint>
+
+#include "mongo/base/disallow_copying.h"
+#include "mongo/base/string_data.h"
+
+namespace mongo {
+
+/**
+ * A utility class for performing itoa style integer formatting. This class is highly optimized
+ * and only really should be used in hot code paths.
+ */
+class ItoA {
+    MONGO_DISALLOW_COPYING(ItoA);
+
+public:
+    explicit ItoA(std::uint32_t i);
+
+    operator StringData() {
+        return {_str, _len};
+    }
+
+private:
+    const char* _str{nullptr};
+    std::size_t _len{0};
+    // 11 is provably the max size we need as int32_t max has 10 digits.
+    char _buf[11];
+};
+
+}  // namespace mongo