Sign extending from a constant bit width in C#

Question

I have a value thats 5 bits in length. 4 bits determine the number and the 5th bit determines the sign, there by holding any value between -16 and +15. How can I accomplish sign extending from a constant bit width in C#? I know in C, I can use something like the follow to accomplish this:

int x; // convert this from using 5 bits to a full int
int r; // resulting sign extended number goes here
struct {signed int x:5;} s;
r = s.x = x;

How can I do something similar to this in C#?

Answer 1

I'm just writing a C function (because I don't really know C#) that will do this using operations that I know are available in C#.

int five_bit_to_signed(int five_bit) {
     int sh = (sizeof(int)*8)-5;
     int x = five_bit << sh; // puts your sign bit in the highest bit.
     return x >> sh;  // since x is signed this is an arithmatic signed shift
}