diff --git a/leveldb/db.go b/leveldb/db.go
index a7a3221..384c498 100644
--- a/leveldb/db.go
+++ b/leveldb/db.go
@@ -116,7 +116,7 @@ func (db *DB) Destroy() {
 }
 
 func (db *DB) Clear() {
-	it := db.Iterator(NewRange(nil, nil), 0)
+	it := db.Iterator(nil, nil, 0, 0)
 	for ; it.Valid(); it.Next() {
 		db.Delete(it.Key())
 	}
@@ -141,14 +141,14 @@ func (db *DB) NewWriteBatch() *WriteBatch {
 	return wb
 }
 
-//limit <= 0, no limit
-func (db *DB) Iterator(r *Range, limit int) *Iterator {
-	return newIterator(db, db.iteratorOpts, r, limit, forward)
+//limit <= 0, unlimit
+func (db *DB) Iterator(min []byte, max []byte, rangeType uint8, limit int) *Iterator {
+	return newIterator(db, db.iteratorOpts, NewRange(min, max, rangeType), limit, IteratorForward)
 }
 
-//limit <= 0, no limit
-func (db *DB) ReverseIterator(r *Range, limit int) *Iterator {
-	return newIterator(db, db.iteratorOpts, r, limit, backward)
+//limit <= 0, unlimit
+func (db *DB) RevIterator(min []byte, max []byte, rangeType uint8, limit int) *Iterator {
+	return newIterator(db, db.iteratorOpts, NewRange(min, max, rangeType), limit, IteratorBackward)
 }
 
 func (db *DB) NewSnapshot() *Snapshot {
diff --git a/leveldb/iterator.go b/leveldb/iterator.go
index 588f09b..01dd0f4 100644
--- a/leveldb/iterator.go
+++ b/leveldb/iterator.go
@@ -5,35 +5,33 @@ import (
 	"github.com/jmhodges/levigo"
 )
 
-const forward uint8 = 0
-const backward uint8 = 1
+const (
+	IteratorForward  uint8 = 0
+	IteratorBackward uint8 = 1
+)
+
+const (
+	RangeClose uint8 = 0x00
+	RangeLOpen uint8 = 0x01
+	RangeROpen uint8 = 0x10
+	RangeOpen  uint8 = 0x11
+)
 
 //min must less or equal than max
-//MinEx if true, range is left open interval (min, ...
-//MaxEx if true, range is right open interval ..., max)
-//Default range is close interval
+//range type:
+//close: [min, max]
+//open: (min, max)
+//lopen: (min, max]
+//ropen: [min, max)
 type Range struct {
 	Min []byte
 	Max []byte
 
-	MinEx bool
-	MaxEx bool
+	Type uint8
 }
 
-func NewRange(min []byte, max []byte) *Range {
-	return &Range{min, max, false, false}
-}
-
-func NewOpenRange(min []byte, max []byte) *Range {
-	return &Range{min, max, true, true}
-}
-
-func NewLOpenRange(min []byte, max []byte) *Range {
-	return &Range{min, max, true, false}
-}
-
-func NewROpenRange(min []byte, max []byte) *Range {
-	return &Range{min, max, true, true}
+func NewRange(min []byte, max []byte, tp uint8) *Range {
+	return &Range{min, max, tp}
 }
 
 type Iterator struct {
@@ -45,7 +43,7 @@ type Iterator struct {
 
 	step int
 
-	//0 for forward, 1 for backward
+	//0 for IteratorForward, 1 for IteratorBackward
 	direction uint8
 }
 
@@ -56,15 +54,16 @@ func newIterator(db *DB, opts *levigo.ReadOptions, r *Range, limit int, directio
 	it.r = r
 	it.limit = limit
 	it.direction = direction
+
 	it.step = 0
 
-	if direction == forward {
+	if direction == IteratorForward {
 		if r.Min == nil {
 			it.it.SeekToFirst()
 		} else {
 			it.it.Seek(r.Min)
 
-			if r.MinEx {
+			if r.Type&RangeLOpen > 0 {
 				if it.Valid() && bytes.Equal(it.Key(), r.Min) {
 					it.it.Next()
 				}
@@ -80,7 +79,7 @@ func newIterator(db *DB, opts *levigo.ReadOptions, r *Range, limit int, directio
 				it.it.Prev()
 			}
 
-			if r.MaxEx {
+			if r.Type&RangeROpen > 0 {
 				if it.Valid() && bytes.Equal(it.Key(), r.Max) {
 					it.it.Prev()
 				}
@@ -100,22 +99,22 @@ func (it *Iterator) Valid() bool {
 		return false
 	}
 
-	if it.direction == forward {
+	if it.direction == IteratorForward {
 		if it.r.Max != nil {
 			r := bytes.Compare(it.Key(), it.r.Max)
-			if !it.r.MaxEx {
-				return !(r > 0)
-			} else {
+			if it.r.Type&RangeROpen > 0 {
 				return !(r >= 0)
+			} else {
+				return !(r > 0)
 			}
 		}
 	} else {
 		if it.r.Min != nil {
 			r := bytes.Compare(it.Key(), it.r.Min)
-			if !it.r.MinEx {
-				return !(r < 0)
-			} else {
+			if it.r.Type&RangeLOpen > 0 {
 				return !(r <= 0)
+			} else {
+				return !(r < 0)
 			}
 		}
 	}
@@ -130,7 +129,7 @@ func (it *Iterator) GetError() error {
 func (it *Iterator) Next() {
 	it.step++
 
-	if it.direction == forward {
+	if it.direction == IteratorForward {
 		it.it.Next()
 	} else {
 		it.it.Prev()
diff --git a/leveldb/leveldb_test.go b/leveldb/leveldb_test.go
index 62f53b9..62cd074 100644
--- a/leveldb/leveldb_test.go
+++ b/leveldb/leveldb_test.go
@@ -129,34 +129,6 @@ func checkIterator(it *Iterator, cv ...int) error {
 	return nil
 }
 
-func testKeyRange(min int, max int) *Range {
-	return &Range{
-		[]byte(fmt.Sprintf("key_%d", min)),
-		[]byte(fmt.Sprintf("key_%d", max)),
-		false,
-		false,
-	}
-}
-
-func testLKeyRange(min int, max int) *Range {
-	r := testKeyRange(min, max)
-	r.MinEx = true
-	return r
-}
-
-func testRKeyRange(min int, max int) *Range {
-	r := testKeyRange(min, max)
-	r.MaxEx = true
-	return r
-}
-
-func testOpenKeyRange(min int, max int) *Range {
-	r := testKeyRange(min, max)
-	r.MinEx = true
-	r.MaxEx = true
-	return r
-}
-
 func TestIterator(t *testing.T) {
 	db := getTestDB()
 
@@ -170,52 +142,56 @@ func TestIterator(t *testing.T) {
 
 	var it *Iterator
 
-	it = db.Iterator(testKeyRange(1, 5), 0)
+	k := func(i int) []byte {
+		return []byte(fmt.Sprintf("key_%d", i))
+	}
+
+	it = db.Iterator(k(1), k(5), RangeClose, 0)
 	if err := checkIterator(it, 1, 2, 3, 4, 5); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.Iterator(testKeyRange(1, 9), 5)
-	if err := checkIterator(it, 1, 2, 3, 4, 5); err != nil {
+	it = db.Iterator(k(1), k(5), RangeClose, 3)
+	if err := checkIterator(it, 1, 2, 3); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.Iterator(testLKeyRange(1, 5), 0)
+	it = db.Iterator(k(1), k(5), RangeLOpen, 0)
 	if err := checkIterator(it, 2, 3, 4, 5); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.Iterator(testRKeyRange(1, 5), 0)
+	it = db.Iterator(k(1), k(5), RangeROpen, 0)
 	if err := checkIterator(it, 1, 2, 3, 4); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.Iterator(testOpenKeyRange(1, 5), 0)
+	it = db.Iterator(k(1), k(5), RangeOpen, 0)
 	if err := checkIterator(it, 2, 3, 4); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.ReverseIterator(testKeyRange(1, 5), 0)
+	it = db.RevIterator(k(1), k(5), RangeClose, 0)
 	if err := checkIterator(it, 5, 4, 3, 2, 1); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.ReverseIterator(testKeyRange(1, 9), 5)
-	if err := checkIterator(it, 9, 8, 7, 6, 5); err != nil {
+	it = db.RevIterator(k(1), k(5), RangeClose, 3)
+	if err := checkIterator(it, 5, 4, 3); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.ReverseIterator(testLKeyRange(1, 5), 0)
+	it = db.RevIterator(k(1), k(5), RangeLOpen, 0)
 	if err := checkIterator(it, 5, 4, 3, 2); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.ReverseIterator(testRKeyRange(1, 5), 0)
+	it = db.RevIterator(k(1), k(5), RangeROpen, 0)
 	if err := checkIterator(it, 4, 3, 2, 1); err != nil {
 		t.Fatal(err)
 	}
 
-	it = db.ReverseIterator(testOpenKeyRange(1, 5), 0)
+	it = db.RevIterator(k(1), k(5), RangeOpen, 0)
 	if err := checkIterator(it, 4, 3, 2); err != nil {
 		t.Fatal(err)
 	}
diff --git a/leveldb/snapshot.go b/leveldb/snapshot.go
index 72eb40f..dbbed3c 100644
--- a/leveldb/snapshot.go
+++ b/leveldb/snapshot.go
@@ -37,13 +37,12 @@ func (s *Snapshot) Get(key []byte) ([]byte, error) {
 	return s.db.db.Get(s.readOpts, key)
 }
 
-//same as db iterator and reverse iterator
-func (s *Snapshot) Iterator(r *Range, limit int) *Iterator {
-	return newIterator(s.db, s.iteratorOpts, r, limit, forward)
+func (s *Snapshot) Iterator(min []byte, max []byte, rangeType uint8, limit int) *Iterator {
+	return newIterator(s.db, s.iteratorOpts, NewRange(min, max, rangeType), limit, IteratorForward)
 }
 
-func (s *Snapshot) ReverseIterator(r *Range, limit int) *Iterator {
-	return newIterator(s.db, s.iteratorOpts, r, limit, backward)
+func (s *Snapshot) RevIterator(min []byte, max []byte, rangeType uint8, limit int) *Iterator {
+	return newIterator(s.db, s.iteratorOpts, NewRange(min, max, rangeType), limit, IteratorBackward)
 }
 
 func (s *Snapshot) GetInt(key []byte) (int64, error) {