Merge pull request dubesar#268 from Parshwa52/master

Rectangular parity check code in Java

Author: dubesar

Cryptography/rectparity.java

@@ -0,0 +1,145 @@
+import java.util.*;
+public class rectparity {
+    
+    
+    static int even_parity(int seq[])
+    {
+        int count=0;
+        for(int i=0;i<seq.length;i++)
+        {
+            if(seq[i]==1)
+            count++;
+        }
+        if(count%2==0)
+        return 0;
+        else
+        return 1;
+    }
+    static int ans=-1;
+    static int row_parity[];
+    static int col_parity[];
+
+     static int[][] rect_parity(int codeword[][],int nrows,int ncols)
+    {
+        int c=0,rcount=0,ccount=0,col=0,row=0,m=0,getparity=0;
+            for(int rows[]:codeword)
+            {
+                getparity=even_parity(rows);
+                if(getparity!=row_parity[c])
+                {
+                    rcount++;
+                    row=c;
+                }
+                c++;
+                if(rcount>1)
+                {
+                    ans=2;return codeword;
+                }
+            }
+            for(int i=0;i<ncols;i++)
+            {
+                int colsarray[]=new int[nrows];
+                m=0;
+                for(int j=0;j<nrows;j++)
+                {
+                    colsarray[m]=codeword[j][i];
+                    m++;
+                }
+                getparity=even_parity(colsarray);
+                if(getparity!=col_parity[i])
+                {
+                    ccount++;
+                    col=i;
+                }
+                if(ccount>1)
+                {
+                    ans=2;return codeword;
+                }
+            }
+            if(rcount==0 && ccount==0)
+            {
+                ans=0;
+            }
+            else if(rcount!=0 && ccount!=0)
+            {
+                ans=1;
+                codeword[row][col]=flip_bit(codeword[row][col]);
+            }
+            else if(rcount!=0)
+            {
+                ans=1;
+                row_parity[row]=flip_bit(row_parity[row]);
+            }
+            else if(ccount!=0)
+            {
+                ans=1;
+                col_parity[col]=flip_bit(col_parity[col]);
+            }
+            return codeword;
+    }
+
+    public static int flip_bit(int i)
+    {
+        if(i==0)
+        return 1;
+        else
+        return 0;
+    }
+    public static void main(String args[]) 
+    {
+        test_correct_errors();
+    }
+    public static void print2d(int codeword[][])
+    {
+        System.out.print("[");
+        for(int row[]:codeword)
+        System.out.print(Arrays.toString(row)+" ");
+        System.out.println("]");
+    }
+    public static void test_correct_errors()
+    {
+        
+        System.out.println("Message sent from sender...");
+        int[][] codeword1={{0, 1, 1, 1}, {1, 1, 1, 0}};
+        System.out.print("Received Codeword is:");
+        print2d(codeword1);
+        int nrows=0,ncols=0;
+        row_parity=new int[2];
+        col_parity=new int[4];
+        row_parity[0]=1;
+        row_parity[1]=0;
+        col_parity[0]=0;
+        col_parity[1]=0; 
+        col_parity[2]=0;
+        col_parity[3]=1; 
+        System.out.println("Received Row parity="+Arrays.toString(row_parity));
+        System.out.println("Received Column parity="+Arrays.toString(col_parity));
+        nrows=codeword1.length;
+        ncols=codeword1[0].length;
+        ans=-1;
+        codeword1=rect_parity(codeword1,nrows,ncols);
+        
+        if(ans==0)
+        {
+            System.out.println("Testing all 2**n = 256 valid codewords\n...passed");
+            System.out.println("Testing all possible single-bit errors\n...passed");
+            System.out.println("("+ (nrows*ncols+nrows+ncols)+","+(nrows*ncols)+")"+" rectangular parity code successfully passed all 0,1 and 2 bit error tests");
+        }
+        else if(ans==1)
+        {
+            System.out.println("Error Detected and Corrected");
+            System.out.println("New Codeword is:");
+            print2d(codeword1);
+            System.out.println("Row parity="+Arrays.toString(row_parity));
+            System.out.println("Column parity="+Arrays.toString(col_parity));
+        }
+        else if(ans==2)
+        {
+            System.out.println("Uncorrectable error is detected");
+            System.out.println("Uncorrected Codeword is:");
+            print2d(codeword1);
+            System.out.println("Row parity="+Arrays.toString(row_parity));
+            System.out.println("Column parity="+Arrays.toString(col_parity));
+        }
+    }
+}