Which bit signs a sbyte?

Question

I understand that an sbyte foregoes a bit in order to "sign" it's value, positive or negative. This naturally leaves 7 bits for the value being 7² = 128 (0 to 127 OR -1 to -128 dependent on the signing bit).

My question is, which of the 8 bits in the byte is the signing bit? I imagine it to be bit 8, the MSB?

I ask since I would of expected byte foo = -1 to explicitly cast to 129 with byte bar = (byte)foo since the underlying bit structure would be 10000001. However, the above returns bar as 255.

Test Code

    sbyte negative = -1;
    sbyte postive = 1;

    byte negativeResult = (byte)(negative & 0b_1000_0001);
    byte positiveResult = (byte)(postive & 0b_1000_0001);

    Console.WriteLine($"Negative evaluated to: {Convert.ToString(negativeResult, toBase: 2)}");
    Console.WriteLine($"Positive evaluated to: {Convert.ToString(positiveResult, toBase: 2)}");

Output

    Negative evaluated to: 10000001
    Positive evaluated to: 1

Does this answer your question? [What is “2's Complement”?](https://stackoverflow.com/questions/1049722/what-is-2s-complement) It is the top bit, but it doesn't work the way you expect. — harold, Nov 15 '20 at 10:48
@harold Thank you, Sir. I hadn't heard the expression "complement" before and I certainly hadn't imagined it to work that way, very interesting! — George Kerwood, Nov 15 '20 at 10:51
@GeorgeKerwood one way you can look at "why does -1 cast to 255", is to ask what should happen when you add 1 to it. You should get zero as the result, right? `(byte)(255+1)` is also zero, in that sense -1 and 255 are just different ways to look at the same thing (all bits set). — harold, Nov 15 '20 at 10:55
@harold. If I've understood correctly therefore, this is exactly why `sbyte -1` casts to `byte 255`, since the bit pattern is maintained as `11111111`? — George Kerwood, Nov 15 '20 at 10:55

Which bit signs a sbyte?

Test Code

Output

0 Answers0