Bit Shifting & Manipulation-CodePudding

I'm trying to work with bit manipulation, and am struggling modifying the bits directly.

I have something as follows:

unsigned char myBits = 128; // 10000000 in binary
myBits = myBits >> 1; // Right shift, so we get 64, or 01000000 in binary

Now, how would I use bit manipulation to modify the first bit after the right shift (01000000) to a 1 (11000000)?

CodePudding user response：

Most implementations will shift a "1" bit in from the left if the type in question is signed and the value is negative.

So you could either change the type to signed char, or do some casting on the unsigned types:

myBits = (unsigned char)((signed char)myBits >> 1);

CodePudding user response：

you need to binary OR it with the shifted value:

myBits |= myBits >> 1;

To set the most significant bit (you can change the type to any integer type and it will work):

myBits |= 1ULL << (sizeof(myBits) * CHAR_BIT - 1);