One-bit Counts between Unique and Sticky

Stoyeʹs one-bit reference tagging scheme can be extended to local counts of two or more via two strategies. The first, suited to pure register transactions, is a cache of referents to two shared references. The analog of Deutschʹs and Bobrowʹs multiple-reference table, this cache is sufficient to manage small counts across successive assignment statements. Thus, accurate reference counts above one can be tracked for short intervals, like those bridging one functionʹs environment to its successorʹs. The second, motivated by runtime stacks that duplicate references, avoids counting any references from the stack. It requires a local pointer-inversion protocol in the mutator, but one still local to the referent and the stack frame. Thus, an accurate reference count of one can be maintained regardless of references from the recursion stack.