add arena package

arena/arena.go

@@ -0,0 +1,28 @@
+package arena
+
+type Arena struct {
+	buf []byte
+
+	size int
+}
+
+func NewArena(size int) *Arena {
+	a := new(Arena)
+
+	a.size = size
+	a.buf = make([]byte, size, size)
+
+	return a
+}
+
+func (a *Arena) Make(size int) []byte {
+	if a.size < size {
+		return make([]byte, size)
+	} else if len(a.buf) < size {
+		a.buf = make([]byte, a.size)
+	}
+
+	b := a.buf[0:size]
+	a.buf = a.buf[size:]
+	return b
+}

arena/arena_test.go

@@ -0,0 +1,28 @@
+package arena
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestArena(t *testing.T) {
+	a := NewArena(100)
+
+	for i := 0; i < 50; i++ {
+		a.buf[i] = 1
+	}
+
+	for i := 50; i < 100; i++ {
+		a.buf[i] = 2
+	}
+
+	b1 := a.Make(50)
+
+	b2 := a.Make(30)
+
+	b3 := a.Make(40)
+
+	fmt.Printf("%p %d\n", b1, b1[49])
+	fmt.Printf("%p %d\n", b2, b2[29])
+	fmt.Printf("%p %d\n", b3, b3[39])
+}