C# Language: Changing the First Four Bits in a Byte

Question

In order to utilize a byte to its fullest potential, I\'m attempting to store two unique values into a byte: one in the first four bits and another in the second four bits. How

Answer 1

Here's some code, but I think the earlier answers will do it for you. This is just to show some sort of test code to copy and past into a simple console project (the WriteBits method by be of help):

static void Main(string[] args)
    {
        int b1 = 255;
        WriteBits(b1);

        int b2 = b1 >> 4;
        WriteBits(b2);

        int b3 = b1 & ~0xF ;
        WriteBits(b3);

        // Store 5 in first nibble
        int b4 = 5 << 4;
        WriteBits(b4);

        // Store 8 in second nibble
        int b5 = 8;
        WriteBits(b5);

        // Store 5 and 8 in first and second nibbles
        int b6 = 0;
        b6 |= (5 << 4) + 8;
        WriteBits(b6);

        // Store 2 and 4 
        int b7 = 0;
        b7 = StoreFirstNibble(2, b7);
        b7 = StoreSecondNibble(4, b7);
        WriteBits(b7);

        // Read First Nibble
        int first = ReadFirstNibble(b7);
        WriteBits(first);

        // Read Second Nibble
        int second = ReadSecondNibble(b7);
        WriteBits(second);
    }

    static int ReadFirstNibble(int storage)
    {
        return storage >> 4;
    }

    static int ReadSecondNibble(int storage)
    {
        return storage &= 0xF;
    }

    static int StoreFirstNibble(int val, int storage)
    {
        return storage |= (val << 4);
    }

    static int StoreSecondNibble(int val, int storage)
    {
        return storage |= val;
    }

    static void WriteBits(int b)
    {
        Console.WriteLine(BitConverter.ToString(BitConverter.GetBytes(b),0));
    }
}

Answer 2

Assuming newVal contains the value you want to store in origVal. Do this for the 4 least significant bits:

byte origVal = ???;
byte newVal = ???
orig = (origVal & 0xF0) + newVal;

and this for the 4 most significant bits:

byte origVal = ???;
byte newVal = ???
orig = (origVal & 0xF) + (newVal << 4);

Answer 3

I know you asked specifically about clearing out the first four bits, which has been answered several times, but I wanted to point out that if you have two values <= decimal 15, you can combine them into 8 bits simply with this:

    public int setBits(int upperFour, int lowerFour)
    {
        return upperFour << 4 | lowerFour;            
    }

The result will be xxxxyyyy where

xxxx = upperFour
yyyy = lowerFour

And that is what you seem to be trying to do.