CSC/ECE 517 Fall 2009/wiki3 2 clone

Clone Detection and Clone Manipulation

Clone Detection

"Software clones are segments of code that are similar according to some definition of similarity" —Ira Baxter, 2002[1]. As per this definition, two code snippets may be similar based on text, syntactic structure or semantics or if they follow same pattern. Two code fragments are similar if their program text is similar. Code snippets may not be semantically equivalent. Such code snippets are also termed as redundant because if one changes then the other also needs to be changed. However, some clones cannot be replaced by another for example, two code snippets may be identical at the textual level but they refer to different variables declared in different places with the same name. Example of such clones is shown below:

Example of such clones is shown below:

 int count = 0;
 int methodA(string str)
 {
       for (int i=0;i<str.length;i++)
       {
          count = count + 1;
       }

 }
 int methodB(string str)
 {
       int count=0;
       for (int i=0;i<str.length;i++)
       {
 	  count = count + 1;
       }
 }

In the above code snippet, count in methodA refers to global variable whereas in methodB it refers to local count variable.

Clone Detection Tools

1. Duploc: This language independent tool helps in clone detection. It offers clicakble matrix display that helps developers to locate the source code snippet that is cloned. This tool includes an information mural algorithm, and it helps the tool to show a matrix of 100,000 lines per side in its entirety on a 600x800 screen[2]. The performance this tool is good for systems of sizes below 1 MLOC. And for maintenance projects those seldom change over time, duplication of code can be identified over night and can be interpreted on next day.
2. Moss:
3. JPlag:
4. Dup:
5. Dotplot:
6. Covet:
7. CloneDR:
8. CLAN:

References

1. http://drops.dagstuhl.de/opus/volltexte/2007/962/pdf/06301.KoschkeRainer.962.pdf
2. http://scg.unibe.ch/archive/papers/Duca99bCodeDuplication.pdf