Compare within half the space

Exactly half a space apart is unequal, but has no defined ordering.

• Let base and candidate be serial labels in the same b-bit space. Equality means their integer labels are identical. For unequal labels, an equivalent way to apply the RFC’s two ordinary-integer cases is d=(candidate−base) modulo 2^b: if 0<d<2^(b−1), the candidate is greater; if d>2^(b−1), it is less (§3.2). The distance expression is an explanatory calculation, not a new permitted serial subtraction operation.
• With eight bits, candidate 44 compared with base 200 has forward distance 100 and is greater. Reverse the question: candidate 200 compared with base 44 has forward distance 156 and is less. Comparing only the raw integers gives the wrong answer at wraparound (§§3.2,5.2).
• At distance exactly 128 in an eight-bit space, the labels are not equal, but neither greater-than nor less-than is defined. The published pairs are 0/128,1/129,…127/255. Implementations are free to return either ordering result or flag an error; users must not depend on a particular outcome (§§3.2,5.2). This helper deliberately returns an explicit undefined classification instead of choosing an ordering.
• At distance zero the serials are equal, not newer and not an undefined half-space pair. Greater-or-equal and less-or-equal extend the defined comparison naturally. A serial comparison is not a universal ordering for arbitrary lists, nor evidence of the date or authenticity of a version (§§3.2,4,9).