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c#bit-shiftuintulong

What is the best way to combine two uints into a ulong in c#

What is the best way to combine two uints into a ulong in c#, setting the high/low uints.

I know bitshifting can do it, but I don't know the syntax, or there maybe other APIs to help like BitConverter, but I don't see a method that does what I want.

Solution 
  • ulong mixed = (ulong)high << 32 | low;

    The cast is very important. If you omit the cast, considering the fact that high is of type uint (which is 32 bits), you'll be shifting a 32 bit value 32 bits to the left. Shift operators on 32 bit variables will use shift stuff by right-hand-side mod 32. Effectively, shifting a uint 32 bits to the left is a no-op. Casting to ulong prevents this.

    Verifying this fact is easy:

    uint test = 1u;
Console.WriteLine(test << 32); // prints 1
Console.WriteLine((ulong)test << 32); // prints (ulong)uint.MaxValue + 1