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authorPieter Wuille <pieter.wuille@gmail.com>2012-10-27 21:08:45 +0200
committerMatt Corallo <git@bluematt.me>2013-01-16 14:34:06 -0500
commit4bedfa9223d38bbc322d19e28ca03417c216700b (patch)
treec3543d441e83cef03cdaf8a0cd70da43fb0d0163 /src/main.h
parentb1f99bed6f0fbbe94e6a3161b49b3f225dec8374 (diff)
Add CPartialMerkleTree
This adds a compact representation for a subset of a merkle tree's nodes.
Diffstat (limited to 'src/main.h')
-rw-r--r--src/main.h90
1 files changed, 90 insertions, 0 deletions
diff --git a/src/main.h b/src/main.h
index 77aac71d22..f6086e92c2 100644
--- a/src/main.h
+++ b/src/main.h
@@ -1110,11 +1110,101 @@ public:
+/** Data structure that represents a partial merkle tree.
+ *
+ * It respresents 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 explorer 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(32.25*N)
+ *
+ * Where N represents the number of leaf nodes of the partial tree. N itself
+ * is bounded by:
+ *
+ * N <= total_transactions
+ * N <= 1 + matched_transactions*tree_height
+ *
+ * The serialization format:
+ * - uint32 total_transactions (4 bytes)
+ * - varint number of hashes (1-3 bytes)
+ * - uint256[] hashes in depth-first order (<= 32*N bytes)
+ * - varint number of bytes of flag bits (1-3 bytes)
+ * - byte[] flag bits, packed per 8 in a byte, least significant bit first (<= 2*N-1 bits)
+ * The size constraints follow from this.
+ */
+class CPartialMerkleTree
+{
+protected:
+ // the total number of transactions in the block
+ unsigned int nTransactions;
+
+ // node-is-parent-of-matched-txid bits
+ std::vector<bool> vBits;
+
+ // txids and internal hashes
+ std::vector<uint256> vHash;
+ // flag set when encountering invalid data
+ bool fBad;
+ // helper function to efficiently calculate the number of nodes at given height in the merkle tree
+ unsigned int CalcTreeWidth(int height) {
+ return (nTransactions+(1 << height)-1) >> height;
+ }
+
+ // calculate the hash of a node in the merkle tree (at leaf level: the txid's themself)
+ uint256 CalcHash(int height, unsigned int pos, const std::vector<uint256> &vTxid);
+
+ // recursive function that traverses tree nodes, storing the data as bits and hashes
+ void TraverseAndBuild(int height, unsigned int pos, const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
+
+ // recursive function that traverses tree nodes, consuming the bits and hashes produced by TraverseAndBuild.
+ // it returns the hash of the respective node.
+ uint256 TraverseAndExtract(int height, unsigned int pos, unsigned int &nBitsUsed, unsigned int &nHashUsed, std::vector<uint256> &vMatch);
+
+public:
+ // serialization implementation
+ IMPLEMENT_SERIALIZE(
+ READWRITE(nTransactions);
+ READWRITE(vHash);
+ std::vector<unsigned char> vBytes;
+ if (fRead) {
+ READWRITE(vBytes);
+ CPartialMerkleTree &us = *(const_cast<CPartialMerkleTree*>(this));
+ us.vBits.resize(vBytes.size() * 8);
+ for (unsigned int p = 0; p < us.vBits.size(); p++)
+ us.vBits[p] = (vBytes[p / 8] & (1 << (p % 8))) != 0;
+ us.fBad = false;
+ } else {
+ vBytes.resize((vBits.size()+7)/8);
+ for (unsigned int p = 0; p < vBits.size(); p++)
+ vBytes[p / 8] |= vBits[p] << (p % 8);
+ READWRITE(vBytes);
+ }
+ )
+
+ // Construct a partial merkle tree from a list of transaction id's, and a mask that selects a subset of them
+ CPartialMerkleTree(const std::vector<uint256> &vTxid, const std::vector<bool> &vMatch);
+ CPartialMerkleTree();
+ // extract the matching txid's represented by this partial merkle tree.
+ // returns the merkle root, or 0 in case of failure
+ uint256 ExtractMatches(std::vector<uint256> &vMatch);
+};
/** Nodes collect new transactions into a block, hash them into a hash tree,