C# Convert negative int to 11 bits

Question

I need to convert numbers in interval [–1024, 1016]. I'm converting to 11 bits like that:

string s = Convert.ToString(value, 2); //Convert to binary in a string

int[] bits = s.PadLeft(11, '0') // Add 0's from left
                     .Select(c => int.Parse(c.ToString())) // convert each char to int
                     .ToArray(); // Convert IEnumerable from select to Array

This works perfectly for signed integers [0, 1016]. But for negative integers I get 32 bits result. Do you have any idea how to convert negative integers to 11 bits array?

Answer 1

If you only care about the first 11 bits, then just apply a mask:

string s = Convert.ToString(value & 2047, 2);

This will restrict the value to at most 11 bits - and for negative numbers, all the "unused" bits will be 1s.

For reference: 2047 is binary 0000 ... 0000 0111 1111 1111, i.e. a mask of the least significant 11 bits.