1	import Base
2	import ./Protocol.bend as Protocol
3	
4	# Reports one representable count update or exhaustion of the backup format.
5	type Decision is Data:
6	  CountContinue{next_count: U32}
7	  CountLimit{}
8	
9	# Increments a cursor count without wrapping its fixed-width representation.
10	def next.checked(count: U32, maximum: Bool) -> Decision:
11	  match maximum:
12	    case True{}: CountLimit{}
13	    case False{}: CountContinue{U32.from_nat(Nat.add(U32.to_nat(count), 1n))}
14	
15	def next.copies(copies: U32 & U32 & U32) -> Decision:
16	  match copies:
17	    case (retained, (checked, _)):
18	      next.checked(retained, U32.is_eq(checked, 4294967295))
19	
20	# Advances a cursor count without wrapping past its representable limit.
21	def next(count: U32) -> Decision:
22	  next.copies(Protocol.u32.duplicate.triple(count))
23	
24	def u32.pair.copied(copies: U32 & U32 & U32) -> U32 & U32:
25	  match copies:
26	    case (first, (second, _)): (first, second)
27	
28	def u32.pair(value: U32) -> U32 & U32:
29	  u32.pair.copied(Protocol.u32.duplicate.triple(value))