| Data structure that represents a partial merkle
| tree.
|
| It represents a subset of the txid’s of a known
| block, in a way that allows recovery of the
| list of txid’s and the merkle root, in an
| authenticated way.
|
| The encoding works as follows: we traverse the
| tree in depth-first order, storing a bit for
| each traversed node, signifying whether the
| node is the parent of at least one matched leaf
| txid (or a matched txid itself). In case we are
| at the leaf level, or this bit is 0, its merkle
| node hash is stored, and its children are not
| explored further. Otherwise, no hash is stored,
| but we recurse into both (or the only) child
| branch. During decoding, the same depth-first
| traversal is performed, consuming bits and
| hashes as they written during encoding.
|
| The serialization is fixed and provides a hard
| guarantee about the encoded size:
|
| SIZE <= 10 + ceil(32.25N)
|
| Where N represents the number of leaf nodes of
| the partial tree. N itself is bounded by:
|
| N <= total_transactions
| N <= 1 + matched_transactionstree_height
|
| The serialization format:
|
| - uint32 total_transactions (4 bytes)
|
| - varint number of hashes (1-3 bytes)
|
| - uint256[] hashes in depth-first order (<=
| 32N bytes)
|
| - varint number of bytes of flag bits (1-3
| bytes)
|
| - byte[] flag bits, packed per 8 in
| a byte, least significant bit
| first (<= 2N-1 bits)
|
| The size constraints follow from this.