C# bitwise rotate left and rotate right

Question

What is the C# equivalent (.NET 2.0) of _rotl and _rotr from C++?

Answer 1

There's no built-in language feature for bit rotation in C#, but these extension methods should do the job:

public static uint RotateLeft(this uint value, int count)
{
    return (value << count) | (value >> (32 - count))
}

public static uint RotateRight(this uint value, int count)
{
    return (value >> count) | (value << (32 - count))
}

Note: As Mehrdad points out, right-shift (>>) for signed integers is a peculiarity: it fills the MSBs with sign bit rather than 0 as it does for unsigned numbers. I've now changed the methods to take and return uint (unsigned 32-bit integer) instead - this is also in greater accordance with the C++ rotl and rotr functions. If you want to rotate integers, just case them before passing, and again cast the return value, of course.

Example usage:

int foo1 = 8.RotateRight(3); // foo1 = 1
int foo2 = int.MinValue.RotateLeft(3); // foo2 = 4

(Note that int.MinValue is 111111111111111111111111 - 32 1s in binary.)