Add benchmarks for writeTxOut.

This commit adds a benchmark for the writeTxOut function.

bench_test.go

@@ -140,3 +140,12 @@ func BenchmarkWriteOutPoint(b *testing.B) {
 		btcwire.TstWriteOutPoint(ioutil.Discard, 0, 0, op)
 	}
 }
+
+// BenchmarkWriteTxOut performs a benchmark on how long it takes to write
+// a transaction output.
+func BenchmarkWriteTxOut(b *testing.B) {
+	txOut := blockOne.Transactions[0].TxOut[0]
+	for i := 0; i < b.N; i++ {
+		btcwire.TstWriteTxOut(ioutil.Discard, 0, 0, txOut)
+	}
+}

internal_test.go

@@ -114,3 +114,9 @@ func TstReadOutPoint(r io.Reader, pver uint32, version uint32, op *OutPoint) err
 func TstWriteOutPoint(w io.Writer, pver uint32, version uint32, op *OutPoint) error {
 	return writeOutPoint(w, pver, version, op)
 }
+
+// TstWriteTxOut makes the internal writeTxOut function available to the test
+// package.
+func TstWriteTxOut(w io.Writer, pver uint32, version uint32, to *TxOut) error {
+	return writeTxOut(w, pver, version, to)
+}

msgtx.go

@@ -339,7 +339,7 @@ func (msg *MsgTx) BtcEncode(w io.Writer, pver uint32) error {
 	}
 
 	for _, to := range msg.TxOut {
-		err = writeTxOut(w, pver, to)
+		err = writeTxOut(w, pver, msg.Version, to)
 		if err != nil {
 			return err
 		}
@@ -551,7 +551,7 @@ func readTxOut(r io.Reader, pver uint32, version uint32, to *TxOut) error {
 
 // writeTxOut encodes to into the bitcoin protocol encoding for a transaction
 // output (TxOut) to w.
-func writeTxOut(w io.Writer, pver uint32, to *TxOut) error {
+func writeTxOut(w io.Writer, pver uint32, version uint32, to *TxOut) error {
 	err := writeElement(w, to.Value)
 	if err != nil {
 		return err