## 3 Code Refactoring Model Based on XML Syntax Tree
### RTL Code Refactoring Model  
XML is a language that conveys content similar to HTML files but lacks own predefined tags. Consequently, designers have the flexibility to customize their own tags in XML based on development requirements. Data in XML files is presented in a clear format, facilitating easy analysis, and attributes can be added to each tag for detailed descriptions. This file format, characterized by potent information storage and data transfer capabilities, enhances the study's capacity to analyze and extract key information from the RTL code, thereby aiding subsequent obfuscation efforts [16]. The XML syntax tree is a hierarchical structure composed of tags in an XML document, their relationships, and attributes. It provides a clear representation of the hierarchical organization of an XML document, treating tags as nodes connected in a tree-like structure. The relationships between these nodes describe the entirety of the project. In the context of expressing RTL code, the root node serves as the entry point for external access, representing the top-level module of the project. Subsequently, the tree is traversed hierarchically from the top-level module, sequentially displaying the information of each module. In the XML syntax tree, each node has a parent node and zero or more child nodes, and the unique parent-child and brother relationships of this tree structure can help clarify the logic inherent in RTL code. As shown in Figure 1, the <always> tag in an XML document is at the outermost level and contains a variety of tags that are either sibling or parent-child. After a detailed analysis of the content within the <always> tag, the corresponding syntax tree is illustrated in Figure 2. The root node of the syntax tree is <always>, and its two sub-tags become sibling nodes at the second level. The sub-tags contained within the second-level node tags further become nodes at the third level, and so on, resulting in the derivation of a comprehensive structure for the syntax tree. Ultimately, when presented with the syntax tree featuring clear relationships, this study reconstructs the RTL code based on the corresponding syntax of the tags and the internal data of the tags. As illustrated in Figure 3, the contents of the <always> tag are derived as RTL code. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Tool** & **Supports Full Syntax** & **Multi-File Processing** & **Format of Parsing Results** \\ \hline Verilator & \(\surd\) & \(\surd\) & XML \\ verilog-perl & & \(\surd\) & Tool Customized Format \\ Pyverilog [15] & & \(\surd\) & AST \\ verilog-parser & \(\surd\) & \(\surd\) & AST \\ \hline \hline \end{tabular} \(\surd\) Meets the corresponding description.  
\end{table} 
Table 1: Advantages and disadvantages of different parsers. Figure 1: The <always> tag and its sub-tags. Figure 2: The corresponding syntax tree generated by parsing tags. An abstraction of the above reveals that the process can be algorithmically determined. The construction of the syntax tree is essentially achieved by leveraging the information contained in the XML file:  
\[R_{t}=Anal(Tag_{xml},\ Name_{xml},\ Rela_{xml}) \tag{1}\]  
where \(R_{t}\) represents the resulting syntax tree, \(Rela_{xml}\) denotes the data relations in XML, and \(Anal\) represents the analysis algorithm. When combining the results of Formula (1) to reshape the RTL code, the emphasis is on the regularity of the derivation process and the correction of syntax:  
\[R_{c}=Der(Trav\_algo(R_{t}),\ Data_{xml},\ Syn_{RTL}) \tag{2}\]  
Here, \(R_{c}\) signifies the refactored RTL code, \(Der\) and \(Trav\_algo\) represent the refactoring and traversal algorithms proposed, while \(Syn_{RTL}\) denotes the categorized RTL grammar. This study integrates and standardizes a series of operations in which a syntax tree is deduced from an XML file content, and then the syntax tree is deduced into RTL code. A refactoring model for RTL code has been formulated based on these operations.