Bring static pointers back to the static table

internal/serde/reflect.go

@@ -215,6 +215,13 @@ func serializePointedAt(s *Serializer, t reflect.Type, p unsafe.Pointer) {
 		return
 	}
 
+	if static(p) {
+		serializeVarint(s, -1)
+		off := staticOffset(p)
+		serializeVarint(s, off)
+		return
+	}
+
 	id, new := s.assignPointerID(p)
 	serializeVarint(s, int(id))
 	if !new {

internal/serde/serde.go

@@ -71,6 +71,15 @@ func newDeserializer(b []byte) *Deserializer {
 func (d *Deserializer) readPtr() (unsafe.Pointer, sID) {
 	x, n := binary.Varint(d.b)
 	d.b = d.b[n:]
+
+	// pointer into static uint64 table
+	if x == -1 {
+		x, n = binary.Varint(d.b)
+		d.b = d.b[n:]
+		p := staticPointer(int(x))
+		return p, 0
+	}
+
 	i := sID(x)
 	p := d.ptrs[i]
 	return p, i

internal/serde/unsafe.go

@@ -36,3 +36,23 @@ func inlined(t reflect.Type) bool {
 		return false
 	}
 }
+
+var staticuint64s unsafe.Pointer
+
+func init() {
+	zero := 0
+	var x interface{} = zero
+	staticuint64s = (*iface)(unsafe.Pointer(&x)).ptr
+}
+
+func static(p unsafe.Pointer) bool {
+	return uintptr(p) >= uintptr(staticuint64s) && uintptr(p) < uintptr(staticuint64s)+256
+}
+
+func staticOffset(p unsafe.Pointer) int {
+	return int(uintptr(p) - uintptr(staticuint64s))
+}
+
+func staticPointer(offset int) unsafe.Pointer {
+	return unsafe.Add(staticuint64s, offset)
+}

serde/serde_test.go

@@ -93,6 +93,16 @@ func TestReflect(t *testing.T) {
 	})
 }
 
+func TestInt257(t *testing.T) {
+	one := 1
+	x := []any{
+		true,
+		one,
+	}
+	serde.RegisterType[[]any]()
+	assertRoundTrip(t, x)
+}
+
 func TestReflectCustom(t *testing.T) {
 	ser := func(s *serde.Serializer, x *int) error {
 		str := strconv.Itoa(*x)