How do I convert hex string into signed integer?

Question

I'm getting a hex string that needs to be converted to a signed 8-bit integer. Currently I'm converting using Int16/Int32, which will obviously not give me a negative value for an 8-bit integer. If I get the value 255 in Hex, how do I convert that to -1 in decimal? I assume I want to use an sbyte, but I'm not sure how to get that value in there properly.

Answer 1

You can use Convert.ToSByte

For example:

string x = "aa";
sbyte v = Convert.ToSByte(x, 16);
// result: v = 0xAA or -86

You can also use sbyte.Parse

For example:

string y = "bb";
sbyte w = sbyte.Parse(y, System.Globalization.NumberStyles.HexNumber);
// result: w = 0xBB or -69

To answer your question about the upper or lower byte of an Int16:

string signed_short = "feff";

// Truncate 16 bit value down to 8 bit
sbyte b1 = (sbyte)Convert.ToInt16(signed_short, 16);
sbyte b2 = (sbyte)short.Parse(signed_short, System.Globalization.NumberStyles.HexNumber);
// result: b1 = 0xFF or -1
// result: b2 = 0xFF or -1

// Use upper 8 bit of 16 bit
sbyte b3 = (sbyte)(Convert.ToInt16(signed_short, 16) >> 8);
sbyte b4 = (sbyte)(short.Parse(signed_short, System.Globalization.NumberStyles.HexNumber) >> 8);
// result: b3 = 0xFE or -2
// result: b4 = 0xFE or -2

Answer 2

You need to perform an unchecked cast, like this:

sbyte negativeOne = unchecked((sbyte)255);