From addb9b5a71ff96bdb1a4c15bc9345de0d7f2c98c Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter@wuille.net>
Date: Thu, 17 Jun 2021 16:54:56 -0700
Subject: Improve comments in taproot signing logic

---
 src/script/interpreter.h | 7 +++++++
 src/script/sign.cpp      | 2 +-
 src/script/standard.h    | 9 ++++++---
 3 files changed, 14 insertions(+), 4 deletions(-)

(limited to 'src/script')

diff --git a/src/script/interpreter.h b/src/script/interpreter.h
index 93136a0b79..ab49e84577 100644
--- a/src/script/interpreter.h
+++ b/src/script/interpreter.h
@@ -170,6 +170,13 @@ struct PrecomputedTransactionData
 
     PrecomputedTransactionData() = default;
 
+    /** Initialize this PrecomputedTransactionData with transaction data.
+     *
+     * @param[in]   tx             The transaction for which data is being precomputed.
+     * @param[in]   spent_outputs  The CTxOuts being spent, one for each tx.vin, in order.
+     * @param[in]   force          Whether to precompute data for all optional features,
+     *                             regardless of what is in the inputs (used at signing
+     *                             time, when the inputs aren't filled in yet). */
     template <class T>
     void Init(const T& tx, std::vector<CTxOut>&& spent_outputs, bool force = false);
 
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 2faf7e5048..2a1c99e387 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -61,7 +61,7 @@ bool MutableTransactionSignatureCreator::CreateSchnorrSig(const SigningProvider&
 
     CKey key;
     {
-        // For now, use the old full pubkey-based key derivation logic. As it indexed by
+        // For now, use the old full pubkey-based key derivation logic. As it is indexed by
         // Hash160(full pubkey), we need to try both a version prefixed with 0x02, and one
         // with 0x03.
         unsigned char b[33] = {0x02};
diff --git a/src/script/standard.h b/src/script/standard.h
index ac4e2f3276..78492733db 100644
--- a/src/script/standard.h
+++ b/src/script/standard.h
@@ -227,8 +227,11 @@ struct TaprootSpendData
     /** The Merkle root of the script tree (0 if no scripts). */
     uint256 merkle_root;
     /** Map from (script, leaf_version) to (sets of) control blocks.
-     *  The control blocks are sorted by size, so that the signing logic can
-     *  easily prefer the cheapest one. */
+     *  More than one control block for a given script is only possible if it
+     *  appears in multiple branches of the tree. We keep them all so that
+     *  inference can reconstruct the full tree. Within each set, the control
+     *  blocks are sorted by size, so that the signing logic can easily
+     *  prefer the cheapest one. */
     std::map<std::pair<CScript, int>, std::set<std::vector<unsigned char>, ShortestVectorFirstComparator>> scripts;
     /** Merge other TaprootSpendData (for the same scriptPubKey) into this. */
     void Merge(TaprootSpendData other);
@@ -252,7 +255,7 @@ private:
         /** Merkle hash of this node. */
         uint256 hash;
         /** Tracked leaves underneath this node (either from the node itself, or its children).
-         *  The merkle_branch field for each is the partners to get to *this* node. */
+         *  The merkle_branch field of each is the partners to get to *this* node. */
         std::vector<LeafInfo> leaves;
     };
     /** Whether the builder is in a valid state so far. */
-- 
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