[FEAT MERGE] [v4.2] add table generator and several random utility functions

src/sql/engine/expr/ob_expr_zipf.h

@@ -0,0 +1,56 @@
+/**
+ * Copyright (c) 2021 OceanBase
+ * OceanBase CE is licensed under Mulan PubL v2.
+ * You can use this software according to the terms and conditions of the Mulan PubL v2.
+ * You may obtain a copy of Mulan PubL v2 at:
+ *          http://license.coscl.org.cn/MulanPubL-2.0
+ * THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, WITHOUT WARRANTIES OF ANY KIND,
+ * EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO NON-INFRINGEMENT,
+ * MERCHANTABILITY OR FIT FOR A PARTICULAR PURPOSE.
+ * See the Mulan PubL v2 for more details.
+ */
+
+#ifndef OCEANBASE_SQL_OB_EXPR_FUNC_ZIPF_H_
+#define OCEANBASE_SQL_OB_EXPR_FUNC_ZIPF_H_
+
+#include <random>
+#include "sql/engine/expr/ob_expr_operator.h"
+
+namespace oceanbase
+{
+namespace sql
+{
+class ObExprZipf : public ObFuncExprOperator
+{
+	class ObExprZipfCtx: public ObExprOperatorCtx
+	{
+	public:
+		ObExprZipfCtx() = default;
+    ~ObExprZipfCtx() = default;
+    int initialize(ObEvalCtx &ctx, const ObExpr &expr);
+    int generate_next_value(int64_t seed, int64_t &result);
+  private:
+    common::ObArray<double> probe_cp_; // cumulative probability array
+    std::mt19937_64 gen_; // map continuous small number to large sparse space
+  };
+public:
+	explicit ObExprZipf(common::ObIAllocator &alloc);
+	virtual ~ObExprZipf();
+  virtual int calc_result_type3(ObExprResType &result_type,
+                                ObExprResType &exponent,
+                                ObExprResType &size,
+                                ObExprResType &rand_expr,
+                                common::ObExprTypeCtx &type_ctx) const;
+  virtual bool need_rt_ctx() const override { return true; }
+  virtual int cg_expr(ObExprCGCtx &expr_cg_ctx,
+                      const ObRawExpr &raw_expr,
+                      ObExpr &rt_expr) const override;
+  static int eval_next_value(const ObExpr &expr, ObEvalCtx &ctx, ObDatum &res_datum);
+private:
+	DISALLOW_COPY_AND_ASSIGN(ObExprZipf);
+};
+
+} /* namespace sql */
+} /* namespace oceanbase */
+
+#endif /* OCEANBASE_SQL_OB_EXPR_FUNC_ZIPF_H_ */