In mathematical notation for numbers, signed-digit representation indicates that each digit is associated with a sign, positive or negative.
Challenges in calculation stimulated early authors Colson (1726) and Cauchy (1840) to use signed-digit representation. The further step of replacing negated digits with new ones was suggested by Selling (1887) and Cajori (1928).
Signed-digit representation can be used in low-level software and hardware to accomplish fast addition of integers because it can eliminate carries. In the binary numeral system one special case of signed-digit representation is the non-adjacent form which can offer speed benefits with minimal space overhead.
Read more about Signed-digit Representation: Balanced Form, Non-unique Representations, Negative Numerals