trees

const MaxSize = 1<<48 - 1

MaxSize is the largest size of tree that can exist, per Section 5.2 of draft-ietf-plants-merkle-tree-certs-07:

> Each issuance log describes an append-only sequence of at most 2^48-1 entries

The max size is 2^48-1, rather than 2^48 as one might expect, because a subtree is represented by the half-open interval [start, end), meaning that `end` is one greater than the largest entry index in the subtree. If the max size of a tree were 2^48, the last entry in that tree would have an entry index of 2^48-1, and a subtree containing that last entry would be described by the pair [xx, 2^48). But the value `end` must fit in 48 bits, and therefore has a maximum value of 2^48-1. Thus we conclude that the maximum entry index must be 2^48-2, and the maximum tree size is 2^48-1.