2’s complement

0 1 2 3 -4 -3 -2 -1 
------------------>

naming rationale: for n-bit integer, sum (x + -x) = 2^n, which is all 0s in n-bit.
- -x is a complement of x with respect to 2^n
representation: sX = -s * 2^(n - 1) + X
- first bit represents -2^(n - 1) (s)
- all other bits are normal binary representation (X)
conversion: 0000 1011
- flip all bits 1111 0100
- then add 1 1111 0101

  0000 1011 = 15
  1111 0101 = -15 = -2^7 + 117 (=111 0101)
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1|0000 0000 = 0 (= 2^8 in unsigned)

Pros:
- arithmetic behaves normally (since there’s only 1 zero)