What is an effective way of repeating bits in C#?

Question

For example, I have a uint with some bits set to 1:
uint x = 0b0000_0100_0010_0000

I need to repeat the bits to the left/right N times. Like this:

Repeat left, N = 1: 0000_1100_0110_0000

Repeat left, N = 2: 0001_1100_1110_0000

Repeat right, N = 4: 0000_0111_1111_1110

So it's like "bitwise shift with repeat". Is there an effective way to achieve this, preferably without looping?

Answer 1

You can achieve this with a recursive function, using a shift operation with a bitwise or:

static uint RepeatBits(uint input, int times, bool left)
{
    if (times == 0)
    {
        return input;
    }
    else 
    {
        return (left ? (input << times) : (input >> times)) | RepeatBits(input, times - 1, left);
    }
}

Usage

uint input = 0b0000_0100_0010_0000;

uint shiftLeft1 = RepeatBits(input, 1, true);
uint shiftLeft2 = RepeatBits(input, 2, true);
uint shiftRight3 = RepeatBits(input, 3, false);

Output

0000_1100_0110_0000
0001_1100_1110_0000
0000_0111_1011_1100