Two's Complement - Potential Ambiguities of Terminology

Potential Ambiguities of Terminology

One should be cautious when using the term two's complement, as it can mean either a number format or a mathematical operator. For example 0111 represents 7 in two's-complement notation, but the two's complement of 7 in a 4-bit system is actually 9 (1001 in binary), and 1001 is the two's complement representation of −7. The statement "convert x to two's complement" may be ambiguous, since it could describe either the process of representing x in two's-complement notation without changing its value, or the calculation of the two's complement, which is the arithmetic negative of x if two's complement representation is used.