Add benchmarks for writeVarInt.

This commit adds a few benchmarks for the writeVarInt function.

bench_test.go

@@ -0,0 +1,43 @@
+// Copyright (c) 2013 Conformal Systems LLC.
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package btcwire_test
+
+import (
+	"github.com/conformal/btcwire"
+	"io/ioutil"
+	"testing"
+)
+
+// BenchmarkWriteVarInt1 performs a benchmark on how long it takes to write
+// a single byte variable length integer.
+func BenchmarkWriteVarInt1(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		btcwire.TstWriteVarInt(ioutil.Discard, 0, 1)
+	}
+}
+
+// BenchmarkWriteVarInt3 performs a benchmark on how long it takes to write
+// a three byte variable length integer.
+func BenchmarkWriteVarInt3(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		btcwire.TstWriteVarInt(ioutil.Discard, 0, 65535)
+	}
+}
+
+// BenchmarkWriteVarInt5 performs a benchmark on how long it takes to write
+// a five byte variable length integer.
+func BenchmarkWriteVarInt5(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		btcwire.TstWriteVarInt(ioutil.Discard, 0, 4294967295)
+	}
+}
+
+// BenchmarkWriteVarInt9 performs a benchmark on how long it takes to write
+// a nine byte variable length integer.
+func BenchmarkWriteVarInt9(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		btcwire.TstWriteVarInt(ioutil.Discard, 0, 18446744073709551615)
+	}
+}