Is one's complement a real-world issue, or just a historical one?

Question

Another question asked about determining odd/evenness in C, and the idiomatic (x & 1) approach was correctly flagged as broken for one\'s complement-based systems, which

Answer 1

Is one's complement a real-world issue, or just a historical one?

Yes, it still used. Its even used in modern Intel processors. From Intel® 64 and IA-32 Architectures Software Developer’s Manual 2A, page 3-8:

3.1.1.8 Description Section

Each instruction is then described by number of information sections. The “Description” section describes the purpose of the instructions and required operands in more detail.

Summary of terms that may be used in the description section:
* Legacy SSE: Refers to SSE, SSE2, SSE3, SSSE3, SSE4, AESNI, PCLMULQDQ and any future instruction sets referencing XMM registers and encoded without a VEX prefix.
* VEX.vvvv. The VEX bitfield specifying a source or destination register (in 1’s complement form).
* rm_field: shorthand for the ModR/M r/m field and any REX.B
* reg_field: shorthand for the ModR/M reg field and any REX.R