bd4e64d1d4
This is mostly a backport of some of the same modifications made in Decred along with a few additional things cleaned up. In particular, this updates the code to make use of the new chainhash package. Also, since this required API changes anyways and the hash algorithm is no longer tied specifically to SHA, all other functions throughout the code base which had "Sha" in their name have been changed to Hash so they are not incorrectly implying the hash algorithm. The following is an overview of the changes: - Remove the wire.ShaHash type - Update all references to wire.ShaHash to the new chainhash.Hash type - Rename the following functions and update all references: - wire.BlockHeader.BlockSha -> BlockHash - wire.MsgBlock.BlockSha -> BlockHash - wire.MsgBlock.TxShas -> TxHashes - wire.MsgTx.TxSha -> TxHash - blockchain.ShaHashToBig -> HashToBig - peer.ShaFunc -> peer.HashFunc - Rename all variables that included sha in their name to include hash instead - Update for function name changes in other dependent packages such as btcutil - Update copyright dates on all modified files - Update glide.lock file to use the required version of btcutil
107 lines
3.7 KiB
Go
107 lines
3.7 KiB
Go
// Copyright (c) 2013-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package blockchain
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import (
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"math"
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"github.com/btcsuite/btcd/chaincfg/chainhash"
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"github.com/btcsuite/btcutil"
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)
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// nextPowerOfTwo returns the next highest power of two from a given number if
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// it is not already a power of two. This is a helper function used during the
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// calculation of a merkle tree.
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func nextPowerOfTwo(n int) int {
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// Return the number if it's already a power of 2.
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if n&(n-1) == 0 {
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return n
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}
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// Figure out and return the next power of two.
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exponent := uint(math.Log2(float64(n))) + 1
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return 1 << exponent // 2^exponent
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}
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// HashMerkleBranches takes two hashes, treated as the left and right tree
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// nodes, and returns the hash of their concatenation. This is a helper
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// function used to aid in the generation of a merkle tree.
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func HashMerkleBranches(left *chainhash.Hash, right *chainhash.Hash) *chainhash.Hash {
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// Concatenate the left and right nodes.
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var hash [chainhash.HashSize * 2]byte
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copy(hash[:chainhash.HashSize], left[:])
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copy(hash[chainhash.HashSize:], right[:])
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newHash := chainhash.DoubleHashH(hash[:])
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return &newHash
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}
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// BuildMerkleTreeStore creates a merkle tree from a slice of transactions,
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// stores it using a linear array, and returns a slice of the backing array. A
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// linear array was chosen as opposed to an actual tree structure since it uses
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// about half as much memory. The following describes a merkle tree and how it
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// is stored in a linear array.
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//
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// A merkle tree is a tree in which every non-leaf node is the hash of its
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// children nodes. A diagram depicting how this works for bitcoin transactions
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// where h(x) is a double sha256 follows:
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//
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// root = h1234 = h(h12 + h34)
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// / \
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// h12 = h(h1 + h2) h34 = h(h3 + h4)
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// / \ / \
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// h1 = h(tx1) h2 = h(tx2) h3 = h(tx3) h4 = h(tx4)
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//
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// The above stored as a linear array is as follows:
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//
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// [h1 h2 h3 h4 h12 h34 root]
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//
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// As the above shows, the merkle root is always the last element in the array.
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//
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// The number of inputs is not always a power of two which results in a
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// balanced tree structure as above. In that case, parent nodes with no
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// children are also zero and parent nodes with only a single left node
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// are calculated by concatenating the left node with itself before hashing.
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// Since this function uses nodes that are pointers to the hashes, empty nodes
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// will be nil.
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func BuildMerkleTreeStore(transactions []*btcutil.Tx) []*chainhash.Hash {
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// Calculate how many entries are required to hold the binary merkle
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// tree as a linear array and create an array of that size.
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nextPoT := nextPowerOfTwo(len(transactions))
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arraySize := nextPoT*2 - 1
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merkles := make([]*chainhash.Hash, arraySize)
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// Create the base transaction hashes and populate the array with them.
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for i, tx := range transactions {
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merkles[i] = tx.Hash()
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}
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// Start the array offset after the last transaction and adjusted to the
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// next power of two.
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offset := nextPoT
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for i := 0; i < arraySize-1; i += 2 {
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switch {
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// When there is no left child node, the parent is nil too.
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case merkles[i] == nil:
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merkles[offset] = nil
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// When there is no right child, the parent is generated by
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// hashing the concatenation of the left child with itself.
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case merkles[i+1] == nil:
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newHash := HashMerkleBranches(merkles[i], merkles[i])
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merkles[offset] = newHash
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// The normal case sets the parent node to the double sha256
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// of the concatentation of the left and right children.
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default:
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newHash := HashMerkleBranches(merkles[i], merkles[i+1])
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merkles[offset] = newHash
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}
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offset++
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}
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return merkles
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}
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