Use math/bits OnesCount to preallocate slices

Author: serprex

client/conn.go

@@ -5,6 +5,7 @@ import (
 "context"
 "crypto/tls"
 "fmt"
+"math/bits"
 "net"
 "runtime"
 "runtime/debug"
@@ -557,8 +558,8 @@ func (c *Conn) execSend(query string) error {
 // separated by "|". Examples of capability names are CLIENT_DEPRECATE_EOF and CLIENT_PROTOCOL_41.
 // These are defined as constants in the mysql package.
 func (c *Conn) CapabilityString() string {
-var caps []string
 capability := c.capability
+caps := make([]string, 0, bits.OnesCount32(capability))
 for i := 0; capability != 0; i++ {
 field := uint32(1 << i)
 if capability&field == 0 {
@@ -642,8 +643,8 @@ func (c *Conn) CapabilityString() string {
 // StatusString returns a "|" separated list of status fields. Example status values are SERVER_QUERY_WAS_SLOW and SERVER_STATUS_AUTOCOMMIT.
 // These are defined as constants in the mysql package.
 func (c *Conn) StatusString() string {
-var stats []string
 status := c.status
+stats := make([]string, 0, bits.OnesCount16(status))
 for i := 0; status != 0; i++ {
 field := uint16(1 << i)
 if status&field == 0 {

replication/row_event.go

@@ -5,6 +5,7 @@ import (
 "encoding/hex"
 "fmt"
 "io"
+"math/bits"
 "strconv"
 "strings"
 "time"
@@ -754,7 +755,7 @@ func (e *TableMapEvent) VisibilityMap() map[int]bool {
 if len(e.VisibilityBitmap) == 0 {
 return nil
 }
-ret := make(map[int]bool)
+ret := make(map[int]bool, len(e.VisibilityBitmap)*8)
 i := 0
 for _, field := range e.VisibilityBitmap {
 for c := 0x80; c != 0; c >>= 1 {
@@ -1146,15 +1147,19 @@ func (e *RowsEvent) decodeImage(data []byte, bitmap []byte, rowImageType EnumRow
 }
 
 row := make([]interface{}, e.ColumnCount)
-skips := make([]int, 0)
 
 // refer: https://github.com/alibaba/canal/blob/c3e38e50e269adafdd38a48c63a1740cde304c67/dbsync/src/main/java/com/taobao/tddl/dbsync/binlog/event/RowsLogBuffer.java#L63
 count := 0
-for i := 0; i < int(e.ColumnCount); i++ {
-if isBitSet(bitmap, i) {
+col := 0
+for ; col+8 < int(e.ColumnCount); col += 8 {
+count += bits.OnesCount8(bitmap[col>>3])
+}
+for ; col < int(e.ColumnCount); col++ {
+if isBitSet(bitmap, col) {
 count++
 }
 }
+skips := make([]int, 0, int(e.ColumnCount)-count)
 count = bitmapByteSize(count)
 
 nullBitmap := data[pos : pos+count]