Merge pull request #1322 from NiklasHeneka/llvmir-mintoken-optLevel

LLVM IR min token and README adjustments

languages/llvmir/README.md

@@ -22,6 +22,20 @@ These include binary and bitwise instructions (like addition and or), memory ope
 
 To use the LLVM IR module, add the `-l llvmir` flag in the CLI, or use a `JPlagOption` object with `new de.jplag.llvmir.LLVMIRLanguage()` as `language` in the Java API as described in the usage information in the [readme of the main project](https://github.com/jplag/JPlag#usage) and [in the wiki](https://github.com/jplag/JPlag/wiki/1.-How-to-Use-JPlag).
 
+We recommend using the [LLVM optimizer](https://llvm.org/docs/CommandGuide/opt.html) to optimize the LLVM IR code before using JPlag.
+In our tests, optimization level 1 showed the best results in plagiarism detection quality and should therefore, be used.
+
+### Minimum Token Match
+
+It can be difficult to find a good value for the minimum token match because the range of possible candidates for low-level languages like the LLVM IR is much larger.
+Values can range between 60 and 70 for code compiled from C to more than 1000 for code compiled from C++.
+From our tests, we calculated a formula that depends on the average lines of code (avg. loc) to determine a value that should provide good results:
+
+min_token_match(x) = 48.2055162 * e^(0.000333593799 * x)
+
+with x = (avg. loc of the LLVM IR code) - (avg. loc of the source code), <br>
+where the source code is the code from which the IR code was generated, for example, the C or C++ code.
+
 <br>
 
 #### Footnotes

languages/llvmir/src/main/java/de/jplag/llvmir/LLVMIRLanguage.java

@@ -13,7 +13,7 @@ public class LLVMIRLanguage extends AbstractAntlrLanguage {
 
     private static final String NAME = "LLVMIR Parser";
     private static final String IDENTIFIER = "llvmir";
-    private static final int DEFAULT_MIN_TOKEN_MATCH = 40;
+    private static final int DEFAULT_MIN_TOKEN_MATCH = 70;
     private static final String[] FILE_EXTENSIONS = {".ll"};
 
     public LLVMIRLanguage() {