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Thread: 2d (4x4) array insdie a 1d array. (Block cipher)

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    Default 2d (4x4) array insdie a 1d array. (Block cipher)

    Hi guys

    I am trying to create my block cipher as part of a uni project and what the block cipher consists of is putting in the characters in blocks of 4x4 arrays and to map it it has a look up. What i think i needto create is a 2d array inside each cell of a 1d array. Please see photo



    Thats what i am tryiring to create ^^ . Has anyone got any suggestions of how i can do this. I eventually need to be able to subsititue different cells from differnet 4x4 arrays


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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    Alternatively, you can create a large 2d array, and then a second array that contains reference numbers to the start of each "block".

    For example:
    //Sentence
    String sentence = "The quick brown  fox jumps over the lazy dog";
    //Number of Columns needed
    int numColumns=sentence.length()/4;
    //Finish last entire block of 4 columns
    while(numColumns%4!=0)
    numColumns++;
    //2D Array for Sentence
    String[][] array = new String[4][numColumns];
    //1D Array for references
    int[] references = new int[numColumns/4];
    //Fill references
    for(int i=0;i<references.length;i++)
    references[i] = i*4;

    I think that is right. Haven't compiled it.
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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    I can get that code to work im taking it a step at a time.

    What i have is i divde the number of chareacters by 16 to give a double number how ever i need to figure out how to make the double always round up to its whole number ( 12.4 > 13, 3.3 >4, 5.9>6). This will allow me to know how many 4x4 blocks to create then i can use the reference for loop to point to the stating coloum of each 4x4 block.. How can i round the double up ?

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    Quote Originally Posted by fortune2k View Post
    I can get that code to work im taking it a step at a time.

    What i have is i divde the number of chareacters by 16 to give a double number how ever i need to figure out how to make the double always round up to its whole number ( 12.4 > 13, 3.3 >4, 5.9>6). This will allow me to know how many 4x4 blocks to create then i can use the reference for loop to point to the stating coloum of each 4x4 block.. How can i round the double up ?
    What you need to do is find out what the next number divisible by 16 from the number of characters. This can be done with the if statement I had above, were you use mod ( % ) to determine if it doesnt divide evenly.

    For example, if sentence.length()%16 == 0, the number is divisible by 16 and you just need to do sentence.length()/16. Otherwise, you want to do (sentence.length()/16)+1.

    That is the most exact way I know of.

    Other ways would be by doing double division and adding .9 to your decimal, but if you have a double like 5.01, then it will not round up.
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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    im a little confussed on how id implement it


    i want somethinbg like


    WHILE text is NOT EVENLY DIVDED BY 16
    {
    plaintext +=d 'a'
    }
    if text is evenly divded by 16
    {
    array [4][blockammount*4]
    }

    so the while loop will keep adding the letter a to the text string until it divides evenly if it does divide eaisly time that number by 4 to give the number of coloums needed in the array

    i have never used mod before so i am a little stuck

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    //Sentence
    		String sentence = "The quick brown fox jumps over the lazy dog";
     
    		//Declare variable for number of columns
    		int numColumns;
     
    		/* Mod the number of characters in the Sentence by 16.
    		 * If the Modding returns 0, it means it is divisible
    		 * and we do not need to round up. If the Modding returns
    		 * anything other than 0, it means it is not divisible and
    		 * we need to round up. To round up, we add 1 "block" (or 16)
    		 * then divide by 16.
    		 */
    		if(sentence.length() % 16 == 0)
    			numColumns = sentence.length()/16;
    		else
    			numColumns = (sentence.length()+16)/16;

    The above code will give you the number of columns, rounded up to the nearest block of 16.
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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    In Java, a multidimensional array is nothing but an array of arrays. So, a char[] is an array where each element holds a char, char[][] is an array where each element is a char[] and char[][][] is an array of char[][].

    For your requirement, you need to declare the array as
    char[][][] myArray = new char[3][4][4];
    Now each of the three elements of myArray is a two dimensional char array of size 4 X 4 -- a char[4][4]

    db

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    Quote Originally Posted by Darryl.Burke View Post
    In Java, a multidimensional array is nothing but an array of arrays. So, a char[] is an array where each element holds a char, char[][] is an array where each element is a char[] and char[][][] is an array of char[][].

    For your requirement, you need to declare the array as
    char[][][] myArray = new char[3][4][4];
    Now each of the three elements of myArray is a two dimensional char array of size 4 X 4 -- a char[4][4]

    db
    right at the moment i have

    int w=0;
      while(w !=hexarray.length)
      {
            for(int x=0; x< BlockArray.length; x++)
            {
                for(int y=0;y<4;y++)
                {
                    for(int z=0;z<4;z++)
                    {
     
                   System.out.print( BlockArray[x][y][z] = hexarray[w]);
     
                    }
     
                }
     
            }
        w++;
       }

    im also tying to fill;e each block coloum by coloum as shown in my pic..

    am I on the right lines to achive this ?

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    im pretty sure that the 3d array isnt what im after ive never used 3d arrays before im thinking it like a cube am i right ?

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    Quote Originally Posted by fortune2k View Post
    right at the moment i have

    int w=0;
      while(w !=hexarray.length)
      {
            for(int x=0; x< BlockArray.length; x++)
            {
                for(int y=0;y<4;y++)
                {
                    for(int z=0;z<4;z++)
                    {
     
                   System.out.print( BlockArray[x][y][z] = hexarray[w]);
     
                    }
     
                }
     
            }
        w++;
       }

    im also tying to fill;e each block coloum by coloum as shown in my pic..

    am I on the right lines to achive this ?
    I have a suggestion which can make things easier if you ever do a multi-dimensional array on a larger scale. Purely for the reason of making things more readable and easier to debug, I have gotten into the habit of breaking down multi-dimensional arrays when accessing indexes. While it provides to actual advantage from the computer's point of view, it makes it a hell of a lot easier to deal with as a human if you have very complex loops.

    Based on your code above, breaking down the array would look like this:
    int w=0;
    while(w !=hexarray.length)
    {
    	for(int x=0; x< BlockArray.length; x++)
    	{
    		char[][] tempArr1 = BlockArray[x];
     
     		for(int y=0;y<4;y++)
    		{
    			char[] tempArr2 = tempArr1[y];
     
    			for(int z=0;z<4;z++)
    			{
       				System.out.print(tempArr2[z] = hexarray[w]);
    			}
    		}
    	}
    	w++;
    }

    While it is unnecessary for a loop as basic as the one you have above, it can be extremely useful for very complex loops that use multi-dimensional arrays.
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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    it needs to be one big array because i need to substitutae a cell in 1 4x4 block with another one in a different 4x4 array

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    I have just took a manual aproach to print out what comes in each block i was trying to put a print statement in the loop but this seems to work
    code:
            for(int x=0; x< BlockArray.length; x++)
            {
                for(int y=0;y<4;y++)
                {
                    for(int z=0;z<4;z++)
                    {
     
                   BlockArray[x][z] [y] = hexarray[w++];
     
                    }
     
                }
     
            }
     
                System.out.println("Length: "+hexarray.length+" Hash array: ");
     
                for(int d=0;d<hexarray.length;d++)
                {
                   System.out.print(hexarray[d]+" ");
                }
     
                System.out.println("\nBlock 1: \n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[0][0][0], BlockArray[0][0][1],BlockArray[0][0][2],BlockArray[0][0][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[0][1][0], BlockArray[0][1][1],BlockArray[0][1][2],BlockArray[0][1][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[0][2][0], BlockArray[0][2][1],BlockArray[0][2][2],BlockArray[0][2][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[0][3][0], BlockArray[0][3][1],BlockArray[0][3][2],BlockArray[0][3][3]+"\n");
     
                System.out.println("Block 2: \n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[1][0][0], BlockArray[1][0][1],BlockArray[1][0][2],BlockArray[1][0][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[1][1][0], BlockArray[1][1][1],BlockArray[1][1][2],BlockArray[1][1][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[1][2][0], BlockArray[1][2][1],BlockArray[1][2][2],BlockArray[1][2][3]+"\n");
                System.out.printf("%4s %4s %4s %4s", BlockArray[1][3][0], BlockArray[1][3][1],BlockArray[1][3][2],BlockArray[1][3][3]+"\n");

    Output:
    Length: 32 Hash array: 
    41 42 43 44 45 46 47 48 49 4a 4b 4c 4d 4e 4f 50 51 30 31 32 33 34 35 36 37 38 39 30 31 32 33 34 
    Block 1: 
     
      41   45   49  4d
      42   46   4a  4e
      43   47   4b  4f
      44   48   4c  50
    Block 2: 
     
      51   33   37  31
      30   34   38  32
      31   35   39  33
      32   36   30  34
     Lenghth of block array 2
    string length: 32

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    Quote Originally Posted by fortune2k View Post
    I have just took a manual aproach to print out what comes in each block i was trying to put a print statement in the loop but this seems to work
    Check out the API for Arrays#deepToString()
    Arrays#deepToString (Java Platform SE 6)

    db
    Last edited by Darryl.Burke; November 16th, 2010 at 10:10 PM. Reason: Grrr, all forums seem to have a problem converting links that contain square array brackets

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    Default Re: 2d (4x4) array insdie a 1d array. (Block cipher)

    brilliant i got it working thanks for your help

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