reduce encoder allocs

Author: IncSW

internal/encoder/dictionary.go

@@ -1,16 +1,51 @@
 package encoder
 
-import "github.com/IncSW/go-bencode/internal"
+import (
+	"sort"
+	"sync"
+
+	"github.com/IncSW/go-bencode/internal"
+)
+
+const stringsArrayLen = 20
+
+var stringsArrayPool = sync.Pool{
+	New: func() interface{} {
+		return &[stringsArrayLen]string{}
+	},
+}
+
+func sortStrings(ss []string) {
+	if len(ss) <= stringsArrayLen {
+		for i := 1; i < len(ss); i++ {
+			for j := i; j > 0; j-- {
+				if ss[j] >= ss[j-1] {
+					break
+				}
+				ss[j], ss[j-1] = ss[j-1], ss[j]
+			}
+		}
+	} else {
+		sort.Strings(ss)
+	}
+}
 
 //go:nosplit
 func (e *Encoder) encodeDictionary(data map[string]interface{}) error {
 	e.grow(1)
 	e.writeByte('d')
-	keys := make([]string, 0, len(data))
+	var keys []string
+	if len(data) <= stringsArrayLen {
+		stringsArray := stringsArrayPool.Get().(*[stringsArrayLen]string)
+		defer stringsArrayPool.Put(stringsArray)
+		keys = stringsArray[:0:len(data)]
+	} else {
+		keys = make([]string, 0, len(data))
+	}
 	for key, _ := range data {
 		keys = append(keys, key)
 	}
-	internal.SortStrings(keys)
+	sortStrings(keys)
 	for _, key := range keys {
 		e.encodeBytes(internal.S2B(key))
 		err := e.encode(data[key])