diff --git a/core/filex/file.go b/core/filex/file.go
index af0794bb..e82fd8c8 100644
--- a/core/filex/file.go
+++ b/core/filex/file.go
@@ -7,6 +7,7 @@ import (
 
 const bufSize = 1024
 
+// FirstLine returns the first line of the file.
 func FirstLine(filename string) (string, error) {
 	file, err := os.Open(filename)
 	if err != nil {
@@ -17,6 +18,7 @@ func FirstLine(filename string) (string, error) {
 	return firstLine(file)
 }
 
+// LastLine returns the last line of the file.
 func LastLine(filename string) (string, error) {
 	file, err := os.Open(filename)
 	if err != nil {
@@ -69,11 +71,11 @@ func lastLine(filename string, file *os.File) (string, error) {
 
 		if buf[n-1] == '\n' {
 			buf = buf[:n-1]
-			n -= 1
+			n--
 		} else {
 			buf = buf[:n]
 		}
-		for n -= 1; n >= 0; n-- {
+		for n--; n >= 0; n-- {
 			if buf[n] == '\n' {
 				return string(append(buf[n+1:], last...)), nil
 			}
diff --git a/core/filex/lookup.go b/core/filex/lookup.go
index 9dfc5c68..d69e42b4 100644
--- a/core/filex/lookup.go
+++ b/core/filex/lookup.go
@@ -5,12 +5,15 @@ import (
 	"os"
 )
 
+// OffsetRange represents a content block of a file.
 type OffsetRange struct {
 	File  string
 	Start int64
 	Stop  int64
 }
 
+// SplitLineChunks splits file into chunks.
+// The whole line are guaranteed to be split in the same chunk.
 func SplitLineChunks(filename string, chunks int) ([]OffsetRange, error) {
 	info, err := os.Stat(filename)
 	if err != nil {
diff --git a/core/filex/progressscanner.go b/core/filex/progressscanner.go
index be0e8611..11f3c1a5 100644
--- a/core/filex/progressscanner.go
+++ b/core/filex/progressscanner.go
@@ -3,8 +3,11 @@ package filex
 import "gopkg.in/cheggaaa/pb.v1"
 
 type (
+	// A Scanner is used to read lines.
 	Scanner interface {
+		// Scan checks if has remaining to read.
 		Scan() bool
+		// Text returns next line.
 		Text() string
 	}
 
@@ -14,6 +17,7 @@ type (
 	}
 )
 
+// NewProgressScanner returns a Scanner with progress indicator.
 func NewProgressScanner(scanner Scanner, bar *pb.ProgressBar) Scanner {
 	return &progressScanner{
 		Scanner: scanner,
diff --git a/core/filex/rangereader.go b/core/filex/rangereader.go
index 74f6fcbe..cd69f678 100644
--- a/core/filex/rangereader.go
+++ b/core/filex/rangereader.go
@@ -5,12 +5,14 @@ import (
 	"os"
 )
 
+// A RangeReader is used to read a range of content from a file.
 type RangeReader struct {
 	file  *os.File
 	start int64
 	stop  int64
 }
 
+// NewRangeReader returns a RangeReader, which will read the range of content from file.
 func NewRangeReader(file *os.File, start, stop int64) *RangeReader {
 	return &RangeReader{
 		file:  file,
@@ -19,6 +21,7 @@ func NewRangeReader(file *os.File, start, stop int64) *RangeReader {
 	}
 }
 
+// Read reads the range of content into p.
 func (rr *RangeReader) Read(p []byte) (n int, err error) {
 	stat, err := rr.file.Stat()
 	if err != nil {
diff --git a/core/stores/redis/redis_test.go b/core/stores/redis/redis_test.go
index 4b009a0c..c76e0fc0 100644
--- a/core/stores/redis/redis_test.go
+++ b/core/stores/redis/redis_test.go
@@ -341,39 +341,38 @@ func TestRedis_GetBit(t *testing.T) {
 	})
 }
 
-func TestRedis_BitCount(t *testing.T)  {
+func TestRedis_BitCount(t *testing.T) {
 	runOnRedis(t, func(client *Redis) {
-		for i := 0; i < 11; i++{
+		for i := 0; i < 11; i++ {
 			err := client.SetBit("key", int64(i), 1)
 			assert.Nil(t, err)
 		}
 
-		_, err := NewRedis(client.Addr,"").BitCount("key",0,-1)
+		_, err := NewRedis(client.Addr, "").BitCount("key", 0, -1)
 		assert.NotNil(t, err)
-		val, err := client.BitCount("key", 0,-1)
+		val, err := client.BitCount("key", 0, -1)
 		assert.Nil(t, err)
 		assert.Equal(t, int64(11), val)
 
-		val, err = client.BitCount("key", 0,0)
+		val, err = client.BitCount("key", 0, 0)
 		assert.Nil(t, err)
 		assert.Equal(t, int64(8), val)
 
-		val, err = client.BitCount("key", 1,1)
+		val, err = client.BitCount("key", 1, 1)
 		assert.Nil(t, err)
 		assert.Equal(t, int64(3), val)
 
-		val, err = client.BitCount("key", 0,1)
+		val, err = client.BitCount("key", 0, 1)
 		assert.Nil(t, err)
 		assert.Equal(t, int64(11), val)
 
-		val, err = client.BitCount("key", 2,2)
+		val, err = client.BitCount("key", 2, 2)
 		assert.Nil(t, err)
 		assert.Equal(t, int64(0), val)
 
 	})
 }
 
-
 func TestRedis_Persist(t *testing.T) {
 	runOnRedis(t, func(client *Redis) {
 		_, err := NewRedis(client.Addr, "").Persist("key")