Signed-digit representation of numbers indicates that values can be prefixed with a − (minus) sign to indicate that they are negative.

Signed-digit representation can be used in low-level software and hardware to accomplish fast high speed 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.

Note that signed-digit representation is not necessarily unique. For instance:

(0 1 1 1) = 4 + 2 + 1 = 7

(1 0 −1 1) = 8 − 2 + 1 = 7

(1 −1 1 1) = 8 − 4 + 2 + 1 = 7

(1 0 0 −1) = 8 − 1 = 7

The non-adjacent form does guarantee a unique representation for every value.