added utility methods ToGwei and ToEth with tests

common/format.go

@@ -18,9 +18,12 @@ package common
 
 import (
 	"fmt"
+	"math/big"
 	"regexp"
 	"strings"
 	"time"
+
+	"github.com/ethereum/go-ethereum/params"
 )
 
 // PrettyDuration is a pretty printed version of a time.Duration value that cuts
@@ -80,3 +83,18 @@ func (t PrettyAge) String() string {
 	}
 	return result
 }
+
+// ToGWei converts the big.Int wei to its gwei string representation.
+func ToGWei(wei *big.Int) string {
+	return ToEth(new(big.Int).Mul(wei, big.NewInt(params.GWei)))
+}
+
+// ToEth converts the big.Int wei to its ether string representation.
+func ToEth(wei *big.Int) string {
+	z, m := new(big.Int).DivMod(wei, big.NewInt(params.Ether), new(big.Int))
+	if m.Cmp(new(big.Int)) == 0 {
+		return z.String()
+	}
+	s := strings.TrimRight(fmt.Sprintf("%018s", m.String()), "0")
+	return z.String() + "." + s
+}

common/format_test.go

@@ -0,0 +1,66 @@
+package common
+
+import (
+	"math/big"
+	"testing"
+)
+
+func TestToGwei(t *testing.T) {
+	var tests = []struct {
+		wei  *big.Int
+		gwei string
+	}{
+		{big.NewInt(0), "0"},
+		{big.NewInt(1), "0.000000001"},
+		{big.NewInt(1000), "0.000001"},
+		{big.NewInt(1000000), "0.001"},
+		{big.NewInt(1000000000), "1"},
+		{big.NewInt(1100000000), "1.1"},
+		{big.NewInt(1000100000), "1.0001"},
+	}
+
+	for _, test := range tests {
+		t.Logf("%v", test.wei)
+		actual := ToGWei(test.wei)
+		if actual != test.gwei {
+			t.Errorf("%v != %v", actual, test.gwei)
+		}
+	}
+}
+
+func TestToEth(t *testing.T) {
+	var tests = []struct {
+		wei *big.Int
+		eth string
+	}{
+		{big.NewInt(0), "0"},
+		{big.NewInt(1), "0.000000000000000001"},
+		{big.NewInt(1000), "0.000000000000001"},
+		{big.NewInt(1000000), "0.000000000001"},
+		{big.NewInt(1000000000), "0.000000001"},
+		{big.NewInt(1000000000000), "0.000001"},
+		{big.NewInt(1000000000000000), "0.001"},
+		{big.NewInt(1000000000000000000), "1"},
+		{big.NewInt(1100000000000000000), "1.1"},
+		{big.NewInt(1000100000000000000), "1.0001"},
+	}
+
+	for _, test := range tests {
+		actual := ToEth(test.wei)
+		if actual != test.eth {
+			t.Errorf("%v != %v", actual, test.eth)
+		}
+	}
+}
+
+func BenchmarkToEth(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		ToEth(big.NewInt(1))
+	}
+}
+
+func BenchmarkToEth2(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		ToEth(big.NewInt(1000000000000000000))
+	}
+}