Binary Conversion , Help please!

[sara77]

I need to convert any integer value greate than 127 to binary value using this example:
Represent the value in binary
(e.g 137 => 1000 1001)
2) Break in up in groups of 7 bits from the lowest significant bit.
(1 | 000 1001)
3) Take the lowest 7 bits and that gives you the lowest byte (0000 1001)
4) For the next group of 7 bits (in the example, this is 000 0001), set the MSB to 1 (which gives 1000 0001 in our example).

Thus 137 becomes:
1000 0001 0000 1001
can anyone help me do this code using | & and shif to left operators

Thanks

[SammyB]

I need to convert any integer value greate than 127 to binary value using this example:
Represent the value in binary
(e.g 137 => 1000 1001)
2) Break in up in groups of 7 bits from the lowest significant bit.
(1 | 000 1001)
3) Take the lowest 7 bits and that gives you the lowest byte (0000 1001)
4) For the next group of 7 bits (in the example, this is 000 0001), set the MSB to 1 (which gives 1000 0001 in our example).

Thus 137 becomes:
1000 0001 0000 1001
can anyone help me do this code using | & and shif to left operators

Thanks

What are you having trouble with? What language are you using? What environment? (Windows App or Web App) Are you trying to create a string or two bytes?

[sara77]

I am using c# and i need to convert any integer greater than 127 to the format i mentioned. it can be sotred in Int32 format after the conversion is done. can you help?
i have a code that doesn't work most of the time!! i want to use | & >>
rather than this long complicated useless code. here is the code:

 
if (bmpWidth < 128 && bmpHeight < 128)
{
    binaryWriter.Write((byte)bmpWidth);
    binaryWriter.Write((byte)bmpHeight);
}
else
{
    String width = null;
    String height = null;
    int multibytes = 0;
    String[] septenaries = null;
    String currentSeptanary = null;
    int septanaryCount = 0;
    int bitCount = 0;
    byte data = 0;
 
    if (bmpWidth > 127)
    {
        width = binaryConvertor(bmpWidth);
        int widthLenght = width.Length;
        multibytes = widthLenght / 7;
        septenaries = new String[multibytes + 1];
        currentSeptanary = null;
        septanaryCount = 0;
        bitCount = 0;
        for (int count = 0; count < widthLenght; count++)
        {
            septanaryCount = count / 7;
            bitCount++;
            currentSeptanary = width[count] + currentSeptanary;
            if (bitCount == 7)
            {
                septenaries[septanaryCount] = currentSeptanary;
                bitCount = 0;
                currentSeptanary = null;
            }
        }
        if (bitCount != 7)
        {
            septenaries[septanaryCount] = currentSeptanary;
        }
        for (int count = septenaries.Length - 1; count >= 0; count--)
        {
            if (count > 0) // all except the last width bytes should have 1 at bit location 8 to undicates that more length bytes are following
            {
                if (septenaries[count].Length < 7)
                {
                    //pad bits upfront until we have 7 characters 
                    int initialLength = septenaries[count].Length;
                    for (int count2 = 0; count2 < 7 - initialLength; count2++)
                    {
                        septenaries[count] = "0" + septenaries[count];
                    }
                }
                //write a '1' at location 8
                septenaries[count] = "1" + septenaries[count];
            }
            else
            {
                septenaries[count] = "0" + septenaries[count]; //last byte, bit location 8 = 0
            }
            data = (byte)Convert.ToInt64(septenaries[count], 2);
            binaryWriter.Write(data);
        }
    }
}
 

[SammyB]

Ouch! Doesn't this do what you want?

        private void button1_Click(object sender, EventArgs e)
        {
            int n = int.Parse(textBox1.Text);
            int lo7 = n & 0x7F;
            int hi7 = n & 0x3F80;
            hi7 <<= hi7;
            if (hi7 != 0) hi7 += 0x8000;
            int m = lo7 + hi7;
            MessageBox.Show(n.ToString("X") + "-->" + m.ToString("X"));
        }
 

[sara77]

This is genius!!!! can you please explain the code a little bit?
for instance for 128 i should get 1000 0001 0000 0000
and for 137 i should get 1000 0001 0000 1001
with your code i get " 8080" for 128
how can i fix this?

Thank you sooooo much
Sarah

[sara77]

The maximum width/height one can have in a byte is 127.
A width of 128 will require two bytes: 1000 0001 0000 0000.
And a width of 137 will be: 1000 0001 0000 1001
The second bytes for the widths 128 and 137 have their first
bits as 0, so there are no more width bytes to follow."

[sara77]

Just to make mayself clear

"560 will be 0x84 0x30 when denoted as a variable length integer. (0x84 - 0x80)*128 + 0x30 = 512+ 48 = 560. "
so i should be able to get "8430" for 560

[SammyB]

This is genius!!!!

Well, I guess that it's not genius if it doesn't work! ;o)

The code should be:

     private void button1_Click(object sender, System.EventArgs e)
     {
         int n = int.Parse(textBox1.Text);
         int lo7 = n & 0x7F;
         int hi7 = n & 0x3F80;
         hi7 = hi7 << 1;
         if (hi7 != 0) hi7 += 0x8000;
         int m = lo7 + hi7;
         MessageBox.Show(n.ToString("X") + "-->" + m.ToString("X"));
     }
 

I created a windows app with a textbox and a button, hence line 1.
When the user enters a number in the textbox and presses the button, line 3 converts it into an int, n.
Line 4 grabs the low order 7 bits ( 7F hex = 111 1111 binary).
Line 5 grabs the high order 7 bits (3F80 hex = 11 1111 1000 0000 binary.
Line 6 shifts the high-order bits left one bit
Line 7 checks if the high-order is non-zero, if it is non-zero, it sets the MSB by adding in that bit (8000 hex = 1000 0000 0000 0000 binary) -- is this what you want to do?
Line 8 just adds the two pieces together.
I could have ored the bits together, but since they were masked, addition was OK and more understandable.
Line 9 shows the input and output in hex.

HTH --Sam

[sara77]

Thank you so much Sam, my code is finally working!! you are a true genius! A++++++++++++++ programmer