The binary representation of +3997 is 1111 1001 1101.
In one's complement this is simply adding a sign bit and inverting all the bits:
1 0000 0110 0010
The two's complement is the one's complement plus 1:
1 0000 0110 0011
That's 13 bits. Normally the sign bit would be at an 8, 16 or 32,... bit boundary.
For -436 it's 10 0100 1100 and 10 bits
