C# Some Math

This is a discussion on C# Some Math within the C# Programming forums, part of the General Programming Boards category; Okay I am screwing around with web sockets and am trying to negotiate a connection but I have to do ...

  1. #1
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    C# Some Math

    Okay I am screwing around with web sockets and am trying to negotiate a connection but I have to do some math to generate a proper negotiation.

    draft-ietf-hybi-thewebsocketprotocol-03 - The WebSocket protocol That is the RFC I am referencing.

    Okay I have the following information:
    Code:
    Key1: 18x 6]8vM;54 *(5:  {   U1]8  z [  8
    Key2: 1_ tx7X d  <  nw  334J702) 7]o}` 0
    Final: Tm[K T2u
    First step is removing all non-numeric characters from key1 and key 2 leaving me with.

    Code:
    Key1: 1868545188
    Key2: 1733470270
    I used a simple regex for that [^[0-9]] that worked fine

    Next I have to calculate the spaces in the original key1 and key 2 which I did sucesfully with a foreach statement.

    Key1 spaces = 12
    Key2 spaces = 10

    Now heres the part I am not sure of and need help on. I need to divide the key1 number by the number of spaces

    1868545188 / 12 155712099
    1733470270 / 10 173347027

    I need to express each of these output as Big Endian 32 bit numbers? Does that mean flip them? how would I do that in C#.

    After that I concatenate the two numbers with the Final and get the md5 sum of that. Again how do I do this in c#. I am currently doing it this way:
    Code:
    MD5CryptoServiceProvider x = new MD5CryptoServiceProvider();
                byte[] output = x.ComputeHash(input);
                string MD5Output = ASCIIEncoding.UTF8.GetString(output);
    If you guys could help me out I would appreciate it. Note the final outcome of those calculations should be a 16 byte 128 bit value, which in this case is: fQJ,fN/4F4!~K~MH

  2. #2
    (?<!re)tired Mario F.'s Avatar
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    I need to express each of these output as Big Endian 32 bit numbers? Does that mean flip them? how would I do that in C#.
    Use BitConverter.GetBytes, reverse the array and put it back to an int (or not, depending on what you want to do next):

    Code:
    int value;
    if (BitConverter.IsLittleEndian)
    {
        byte[] temp = BitConverter.GetBytes(155712099);
        Array.Reverse(temp);
        value = BitConverter.ToInt32(temp);
    }
    After that I concatenate the two numbers with the Final and get the md5 sum of that. Again how do I do this in c#
    See the System.Security.Cryptography.MD5 class
    The programmer’s wife tells him: “Run to the store and pick up a loaf of bread. If they have eggs, get a dozen.”
    The programmer comes home with 12 loaves of bread.


    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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    Yes, reversing the arrays for the two ints is required.

    Just a small point, but if you're already looping through the chars of each key to count the spaces, you could use that same loop to check for numbers.

    Code:
            static int NumberFromKey(String key, out int spaces)
            {
                spaces = 0;
                String str = String.Empty;
    
                // why bother with regex if you're already looping to count spaces?
                foreach (char c in key.ToCharArray())
                    if (c == ' ')
                        spaces++;
                    else if (Char.IsDigit(c))
                        str += c.ToString();
    
                return int.Parse(str);
            }

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