Pool allocate arrays instead of slices

This is inspired by https://go-review.googlesource.com/c/net/+/539915

common/buf/alloc.go

@@ -8,7 +8,7 @@ import (
 	"sync"
 )
 
-var DefaultAllocator = newDefaultAllocer()
+var DefaultAllocator = newDefaultAllocator()
 
 type Allocator interface {
 	Get(size int) []byte
@@ -17,22 +17,34 @@ type Allocator interface {
 
 // defaultAllocator for incoming frames, optimized to prevent overwriting after zeroing
 type defaultAllocator struct {
-	buffers []sync.Pool
+	buffers [17]sync.Pool
 }
 
 // NewAllocator initiates a []byte allocator for frames less than 65536 bytes,
 // the waste(memory fragmentation) of space allocation is guaranteed to be
 // no more than 50%.
-func newDefaultAllocer() Allocator {
-	alloc := new(defaultAllocator)
-	alloc.buffers = make([]sync.Pool, 17) // 1B -> 64K
-	for k := range alloc.buffers {
-		i := k
-		alloc.buffers[k].New = func() any {
-			return make([]byte, 1<<uint32(i))
-		}
+func newDefaultAllocator() Allocator {
+	return &defaultAllocator{
+		buffers: [...]sync.Pool{ // 1B -> 64K
+			{New: func() any { return new([1]byte) }},
+			{New: func() any { return new([1 << 1]byte) }},
+			{New: func() any { return new([1 << 2]byte) }},
+			{New: func() any { return new([1 << 3]byte) }},
+			{New: func() any { return new([1 << 4]byte) }},
+			{New: func() any { return new([1 << 5]byte) }},
+			{New: func() any { return new([1 << 6]byte) }},
+			{New: func() any { return new([1 << 7]byte) }},
+			{New: func() any { return new([1 << 8]byte) }},
+			{New: func() any { return new([1 << 9]byte) }},
+			{New: func() any { return new([1 << 10]byte) }},
+			{New: func() any { return new([1 << 11]byte) }},
+			{New: func() any { return new([1 << 12]byte) }},
+			{New: func() any { return new([1 << 13]byte) }},
+			{New: func() any { return new([1 << 14]byte) }},
+			{New: func() any { return new([1 << 15]byte) }},
+			{New: func() any { return new([1 << 16]byte) }},
+		},
 	}
-	return alloc
 }
 
 // Get a []byte from pool with most appropriate cap
@@ -41,12 +53,50 @@ func (alloc *defaultAllocator) Get(size int) []byte {
 		return nil
 	}
 
-	bits := msb(size)
-	if size == 1<<bits {
-		return alloc.buffers[bits].Get().([]byte)[:size]
+	index := msb(size)
+	if size != 1<<index {
+		index += 1
 	}
 
-	return alloc.buffers[bits+1].Get().([]byte)[:size]
+	buffer := alloc.buffers[index].Get()
+	switch index {
+	case 0:
+		return buffer.(*[1]byte)[:size]
+	case 1:
+		return buffer.(*[1 << 1]byte)[:size]
+	case 2:
+		return buffer.(*[1 << 2]byte)[:size]
+	case 3:
+		return buffer.(*[1 << 3]byte)[:size]
+	case 4:
+		return buffer.(*[1 << 4]byte)[:size]
+	case 5:
+		return buffer.(*[1 << 5]byte)[:size]
+	case 6:
+		return buffer.(*[1 << 6]byte)[:size]
+	case 7:
+		return buffer.(*[1 << 7]byte)[:size]
+	case 8:
+		return buffer.(*[1 << 8]byte)[:size]
+	case 9:
+		return buffer.(*[1 << 9]byte)[:size]
+	case 10:
+		return buffer.(*[1 << 10]byte)[:size]
+	case 11:
+		return buffer.(*[1 << 11]byte)[:size]
+	case 12:
+		return buffer.(*[1 << 12]byte)[:size]
+	case 13:
+		return buffer.(*[1 << 13]byte)[:size]
+	case 14:
+		return buffer.(*[1 << 14]byte)[:size]
+	case 15:
+		return buffer.(*[1 << 15]byte)[:size]
+	case 16:
+		return buffer.(*[1 << 16]byte)[:size]
+	default:
+		panic("invalid pool index")
+	}
 }
 
 // Put returns a []byte to pool for future use,
@@ -56,10 +106,48 @@ func (alloc *defaultAllocator) Put(buf []byte) error {
 	if cap(buf) == 0 || cap(buf) > 65536 || cap(buf) != 1<<bits {
 		return errors.New("allocator Put() incorrect buffer size")
 	}
+	buf = buf[:cap(buf)]
 
 	//nolint
 	//lint:ignore SA6002 ignore temporarily
-	alloc.buffers[bits].Put(buf)
+	switch bits {
+	case 0:
+		alloc.buffers[bits].Put((*[1]byte)(buf))
+	case 1:
+		alloc.buffers[bits].Put((*[1 << 1]byte)(buf))
+	case 2:
+		alloc.buffers[bits].Put((*[1 << 2]byte)(buf))
+	case 3:
+		alloc.buffers[bits].Put((*[1 << 3]byte)(buf))
+	case 4:
+		alloc.buffers[bits].Put((*[1 << 4]byte)(buf))
+	case 5:
+		alloc.buffers[bits].Put((*[1 << 5]byte)(buf))
+	case 6:
+		alloc.buffers[bits].Put((*[1 << 6]byte)(buf))
+	case 7:
+		alloc.buffers[bits].Put((*[1 << 7]byte)(buf))
+	case 8:
+		alloc.buffers[bits].Put((*[1 << 8]byte)(buf))
+	case 9:
+		alloc.buffers[bits].Put((*[1 << 9]byte)(buf))
+	case 10:
+		alloc.buffers[bits].Put((*[1 << 10]byte)(buf))
+	case 11:
+		alloc.buffers[bits].Put((*[1 << 11]byte)(buf))
+	case 12:
+		alloc.buffers[bits].Put((*[1 << 12]byte)(buf))
+	case 13:
+		alloc.buffers[bits].Put((*[1 << 13]byte)(buf))
+	case 14:
+		alloc.buffers[bits].Put((*[1 << 14]byte)(buf))
+	case 15:
+		alloc.buffers[bits].Put((*[1 << 15]byte)(buf))
+	case 16:
+		alloc.buffers[bits].Put((*[1 << 16]byte)(buf))
+	default:
+		panic("invalid pool index")
+	}
 	return nil
 }