Move BlockMerkleBranch back to merkle.{h,cpp}

The Mining interface uses this function in the next commit
to calculate the coinbase merkle path. Stratum v2 uses
this to send a compact work template.

This partially undoes the change in 4defdfab94,
but is not a revert, because the implementation changed in the meantime.

This commit also documents the function.

src/consensus/merkle.cpp

@@ -83,3 +83,106 @@ uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated)
     return ComputeMerkleRoot(std::move(leaves), mutated);
 }
 
+/* This implements a constant-space merkle root/path calculator, limited to 2^32 leaves. */
+static void MerkleComputation(const std::vector<uint256>& leaves, uint256* proot, bool* pmutated, uint32_t branchpos, std::vector<uint256>* pbranch) {
+    if (pbranch) pbranch->clear();
+    if (leaves.size() == 0) {
+        if (pmutated) *pmutated = false;
+        if (proot) *proot = uint256();
+        return;
+    }
+    bool mutated = false;
+    // count is the number of leaves processed so far.
+    uint32_t count = 0;
+    // inner is an array of eagerly computed subtree hashes, indexed by tree
+    // level (0 being the leaves).
+    // For example, when count is 25 (11001 in binary), inner[4] is the hash of
+    // the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
+    // the last leaf. The other inner entries are undefined.
+    uint256 inner[32];
+    // Which position in inner is a hash that depends on the matching leaf.
+    int matchlevel = -1;
+    // First process all leaves into 'inner' values.
+    while (count < leaves.size()) {
+        uint256 h = leaves[count];
+        bool matchh = count == branchpos;
+        count++;
+        int level;
+        // For each of the lower bits in count that are 0, do 1 step. Each
+        // corresponds to an inner value that existed before processing the
+        // current leaf, and each needs a hash to combine it.
+        for (level = 0; !(count & ((uint32_t{1}) << level)); level++) {
+            if (pbranch) {
+                if (matchh) {
+                    pbranch->push_back(inner[level]);
+                } else if (matchlevel == level) {
+                    pbranch->push_back(h);
+                    matchh = true;
+                }
+            }
+            mutated |= (inner[level] == h);
+            h = Hash(inner[level], h);
+        }
+        // Store the resulting hash at inner position level.
+        inner[level] = h;
+        if (matchh) {
+            matchlevel = level;
+        }
+    }
+    // Do a final 'sweep' over the rightmost branch of the tree to process
+    // odd levels, and reduce everything to a single top value.
+    // Level is the level (counted from the bottom) up to which we've sweeped.
+    int level = 0;
+    // As long as bit number level in count is zero, skip it. It means there
+    // is nothing left at this level.
+    while (!(count & ((uint32_t{1}) << level))) {
+        level++;
+    }
+    uint256 h = inner[level];
+    bool matchh = matchlevel == level;
+    while (count != ((uint32_t{1}) << level)) {
+        // If we reach this point, h is an inner value that is not the top.
+        // We combine it with itself (Bitcoin's special rule for odd levels in
+        // the tree) to produce a higher level one.
+        if (pbranch && matchh) {
+            pbranch->push_back(h);
+        }
+        h = Hash(h, h);
+        // Increment count to the value it would have if two entries at this
+        // level had existed.
+        count += ((uint32_t{1}) << level);
+        level++;
+        // And propagate the result upwards accordingly.
+        while (!(count & ((uint32_t{1}) << level))) {
+            if (pbranch) {
+                if (matchh) {
+                    pbranch->push_back(inner[level]);
+                } else if (matchlevel == level) {
+                    pbranch->push_back(h);
+                    matchh = true;
+                }
+            }
+            h = Hash(inner[level], h);
+            level++;
+        }
+    }
+    // Return result.
+    if (pmutated) *pmutated = mutated;
+    if (proot) *proot = h;
+}
+
+static std::vector<uint256> ComputeMerkleBranch(const std::vector<uint256>& leaves, uint32_t position) {
+    std::vector<uint256> ret;
+    MerkleComputation(leaves, nullptr, nullptr, position, &ret);
+    return ret;
+}
+
+std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position)
+{
+    std::vector<uint256> leaves;
+    leaves.resize(block.vtx.size());
+    for (size_t s = 0; s < block.vtx.size(); s++) {
+        leaves[s] = block.vtx[s]->GetHash();
+    }
+    return ComputeMerkleBranch(leaves, position);
+}

src/consensus/merkle.h

@@ -24,4 +24,14 @@ uint256 BlockMerkleRoot(const CBlock& block, bool* mutated = nullptr);
  */
 uint256 BlockWitnessMerkleRoot(const CBlock& block, bool* mutated = nullptr);
 
+/**
+ * Compute merkle path to the specified transaction
+ *
+ * @param[in] block the block
+ * @param[in] position transaction for which to calculate the merkle path, defaults to coinbase
+ *
+ * @return merkle path ordered from the deepest
+ */
+std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position = 0);
+
 #endif // BITCOIN_CONSENSUS_MERKLE_H

src/test/merkle_tests.cpp

@@ -23,110 +23,6 @@ static uint256 ComputeMerkleRootFromBranch(const uint256& leaf, const std::vecto
     return hash;
 }
 
-/* This implements a constant-space merkle root/path calculator, limited to 2^32 leaves. */
-static void MerkleComputation(const std::vector<uint256>& leaves, uint256* proot, bool* pmutated, uint32_t branchpos, std::vector<uint256>* pbranch) {
-    if (pbranch) pbranch->clear();
-    if (leaves.size() == 0) {
-        if (pmutated) *pmutated = false;
-        if (proot) *proot = uint256();
-        return;
-    }
-    bool mutated = false;
-    // count is the number of leaves processed so far.
-    uint32_t count = 0;
-    // inner is an array of eagerly computed subtree hashes, indexed by tree
-    // level (0 being the leaves).
-    // For example, when count is 25 (11001 in binary), inner[4] is the hash of
-    // the first 16 leaves, inner[3] of the next 8 leaves, and inner[0] equal to
-    // the last leaf. The other inner entries are undefined.
-    uint256 inner[32];
-    // Which position in inner is a hash that depends on the matching leaf.
-    int matchlevel = -1;
-    // First process all leaves into 'inner' values.
-    while (count < leaves.size()) {
-        uint256 h = leaves[count];
-        bool matchh = count == branchpos;
-        count++;
-        int level;
-        // For each of the lower bits in count that are 0, do 1 step. Each
-        // corresponds to an inner value that existed before processing the
-        // current leaf, and each needs a hash to combine it.
-        for (level = 0; !(count & ((uint32_t{1}) << level)); level++) {
-            if (pbranch) {
-                if (matchh) {
-                    pbranch->push_back(inner[level]);
-                } else if (matchlevel == level) {
-                    pbranch->push_back(h);
-                    matchh = true;
-                }
-            }
-            mutated |= (inner[level] == h);
-            h = Hash(inner[level], h);
-        }
-        // Store the resulting hash at inner position level.
-        inner[level] = h;
-        if (matchh) {
-            matchlevel = level;
-        }
-    }
-    // Do a final 'sweep' over the rightmost branch of the tree to process
-    // odd levels, and reduce everything to a single top value.
-    // Level is the level (counted from the bottom) up to which we've sweeped.
-    int level = 0;
-    // As long as bit number level in count is zero, skip it. It means there
-    // is nothing left at this level.
-    while (!(count & ((uint32_t{1}) << level))) {
-        level++;
-    }
-    uint256 h = inner[level];
-    bool matchh = matchlevel == level;
-    while (count != ((uint32_t{1}) << level)) {
-        // If we reach this point, h is an inner value that is not the top.
-        // We combine it with itself (Bitcoin's special rule for odd levels in
-        // the tree) to produce a higher level one.
-        if (pbranch && matchh) {
-            pbranch->push_back(h);
-        }
-        h = Hash(h, h);
-        // Increment count to the value it would have if two entries at this
-        // level had existed.
-        count += ((uint32_t{1}) << level);
-        level++;
-        // And propagate the result upwards accordingly.
-        while (!(count & ((uint32_t{1}) << level))) {
-            if (pbranch) {
-                if (matchh) {
-                    pbranch->push_back(inner[level]);
-                } else if (matchlevel == level) {
-                    pbranch->push_back(h);
-                    matchh = true;
-                }
-            }
-            h = Hash(inner[level], h);
-            level++;
-        }
-    }
-    // Return result.
-    if (pmutated) *pmutated = mutated;
-    if (proot) *proot = h;
-}
-
-static std::vector<uint256> ComputeMerkleBranch(const std::vector<uint256>& leaves, uint32_t position) {
-    std::vector<uint256> ret;
-    MerkleComputation(leaves, nullptr, nullptr, position, &ret);
-    return ret;
-}
-
-static std::vector<uint256> BlockMerkleBranch(const CBlock& block, uint32_t position)
-{
-    std::vector<uint256> leaves;
-    leaves.resize(block.vtx.size());
-    for (size_t s = 0; s < block.vtx.size(); s++) {
-        leaves[s] = block.vtx[s]->GetHash();
-    }
-    return ComputeMerkleBranch(leaves, position);
-}
-
 // Older version of the merkle root computation code, for comparison.
 static uint256 BlockBuildMerkleTree(const CBlock& block, bool* fMutated, std::vector<uint256>& vMerkleTree)
 {