Comments.

Author: evoskuil

include/bitcoin/system/impl/machine/interpreter.ipp

@@ -1025,7 +1025,7 @@ op_check_sig_verify() NOEXCEPT
         // If signature is not empty, it is validated against public key.
         if (key->size() == schnorr::public_key_size)
         {
-            // Split signature and signature hash flags.
+            // Split endorsement into schnorr sig and signature hash flags.
             uint8_t sighash_flags;
             const auto& sig = state::schnorr_split(sighash_flags, *endorsement);
             if (sighash_flags == chain::coverage::invalid)
@@ -1160,7 +1160,7 @@ op_check_multisig_verify() NOEXCEPT
         if (endorsement->empty())
             continue;
 
-        // Split endorsement into DER signature signature hash flags.
+        // Split endorsement into DER signature and signature hash flags.
         uint8_t sighash_flags;
         const auto& der = state::ecdsa_split(sighash_flags, *endorsement);
 
@@ -1303,7 +1303,7 @@ op_check_sig_add() NOEXCEPT
         return error::op_success;
     }
 
-    // Split signature and signature hash flags.
+    // Split endorsement into schnorr signature and signature hash flags.
     uint8_t sighash_flags;
     const auto& sig = state::schnorr_split(sighash_flags, *endorsement);
     if (sighash_flags == chain::coverage::invalid)

include/bitcoin/system/impl/machine/interpreter_connect.ipp

@@ -193,6 +193,7 @@ code CLASS::connect_witness(const chain::context& state,
             if ((ec = input.witness().extract_script(script, stack, prevout)))
                 return ec;
 
+            // TODO: either TAPROOT or TAPSCRIPT.
             interpreter program(tx, it, script, flags, version, stack, {});
 
             if ((ec = program.run()))

include/bitcoin/system/impl/machine/program_sign.ipp

@@ -80,6 +80,8 @@ schnorr_split(uint8_t& sighash_flags, const data_chunk& endorsement) NOEXCEPT
     {
         // BIP341: signature has sighash byte appended in the usual fashion.
         const auto byte = endorsement.back();
+
+        // BIP341: Defined sighash type required (otherwise invalid is set).
         if (is_schnorr_sighash(byte))
             sighash_flags = byte;
     }

src/chain/transaction_sign.cpp

@@ -207,7 +207,7 @@ void transaction::signature_hash_single(writer& sink,
         for (size_t output = 0; output < index; ++output)
             sink.write_bytes(null_output());
 
-        // Guarded by unversioned_sighash.
+        // Guarded by unversioned_sighash().
         outputs_->at(index)->to_data(sink);
     };
 
@@ -306,7 +306,7 @@ bool transaction::unversioned_sighash(hash_digest& out,
     const input_iterator& input, const script& subscript,
     uint8_t sighash_flags) const NOEXCEPT
 {
-    // Set options.
+    // Mask anyone_can_pay and unused bits, and set hash_all by default.
     const auto flag = mask_sighash(sighash_flags);
 
     //*************************************************************************