Add benchmarks for readVarInt.

This commit adds a few benchmarks for the readVarInt function.

bench_test.go

@@ -5,6 +5,7 @@
 package btcwire_test
 
 import (
+	"bytes"
 	"github.com/conformal/btcwire"
 	"io/ioutil"
 	"testing"
@@ -41,3 +42,39 @@ func BenchmarkWriteVarInt9(b *testing.B) {
 		btcwire.TstWriteVarInt(ioutil.Discard, 0, 18446744073709551615)
 	}
 }
+
+// BenchmarkReadVarInt1 performs a benchmark on how long it takes to write
+// a single byte variable length integer.
+func BenchmarkReadVarInt1(b *testing.B) {
+	buf := []byte{0x01}
+	for i := 0; i < b.N; i++ {
+		btcwire.TstReadVarInt(bytes.NewBuffer(buf), 0)
+	}
+}
+
+// BenchmarkReadVarInt3 performs a benchmark on how long it takes to write
+// a three byte variable length integer.
+func BenchmarkReadVarInt3(b *testing.B) {
+	buf := []byte{0x0fd, 0xff, 0xff}
+	for i := 0; i < b.N; i++ {
+		btcwire.TstReadVarInt(bytes.NewBuffer(buf), 0)
+	}
+}
+
+// BenchmarkReadVarInt5 performs a benchmark on how long it takes to write
+// a five byte variable length integer.
+func BenchmarkReadVarInt5(b *testing.B) {
+	buf := []byte{0xfe, 0xff, 0xff, 0xff, 0xff}
+	for i := 0; i < b.N; i++ {
+		btcwire.TstReadVarInt(bytes.NewBuffer(buf), 0)
+	}
+}
+
+// BenchmarkReadVarInt9 performs a benchmark on how long it takes to write
+// a nine byte variable length integer.
+func BenchmarkReadVarInt9(b *testing.B) {
+	buf := []byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
+	for i := 0; i < b.N; i++ {
+		btcwire.TstReadVarInt(bytes.NewBuffer(buf), 0)
+	}
+}