rlp: add big.Int decoder benchmark

rlp/decode_test.go

@@ -26,6 +26,8 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+
+	"github.com/ethereum/go-ethereum/common/math"
 )
 
 func TestStreamKind(t *testing.T) {
@@ -1104,8 +1106,28 @@ func BenchmarkDecodeByteArrayStruct(b *testing.B) {
 
 	var out byteArrayStruct
 	for i := 0; i < b.N; i++ {
-		err := DecodeBytes(enc, &out)
-		if err != nil {
+		if err := DecodeBytes(enc, &out); err != nil {
+			b.Fatal(err)
+		}
+	}
+}
+
+func BenchmarkDecodeBigInts(b *testing.B) {
+	ints := make([]*big.Int, 200)
+	for i := range ints {
+		ints[i] = math.BigPow(2, int64(i))
+	}
+	enc, err := EncodeToBytes(ints)
+	if err != nil {
+		b.Fatal(err)
+	}
+	b.SetBytes(int64(len(enc)))
+	b.ReportAllocs()
+	b.ResetTimer()
+
+	var out []*big.Int
+	for i := 0; i < b.N; i++ {
+		if err := DecodeBytes(enc, &out); err != nil {
 			b.Fatal(err)
 		}
 	}