1 files changed, 69 insertions, 0 deletions
diff --git a/weed/data/datum.go b/weed/data/datum.go
new file mode 100644
index 000000000..5805b691d
--- /dev/null
+++ b/weed/data/datum.go
@@ -0,0 +1,69 @@
+package data
+
+import "fmt"
+
+type Datum interface {
+	Compare(other Datum) (int, error)
+}
+type Datums []Datum
+
+type DUint16 uint16
+type DUint32 uint32
+type dNull struct{}
+
+var (
+	DNull Datum = dNull{}
+)
+
+func (d dNull) Compare(other Datum) (int, error) {
+	if other == DNull {
+		return 0, nil
+	}
+	return -1, nil
+}
+
+func NewDUint16(d DUint16) *DUint16 {
+	return &d
+}
+func NewDUint32(d DUint32) *DUint32 {
+	return &d
+}
+
+func (d *DUint16) Compare(other Datum) (int, error) {
+	if other == DNull {
+		return 1, nil
+	}
+	thisV := *d
+	var otherV DUint16
+	switch t := other.(type) {
+	case *DUint16:
+		otherV = *t
+	default:
+		return 0, fmt.Errorf("unsupported")
+	}
+	if thisV < otherV {
+		return -1, nil
+	}
+	if thisV > otherV {
+		return 1, nil
+	}
+	return 0, nil
+}
+func (d *DUint32) Compare(other Datum) (int, error) {
+	if other == DNull {
+		return 1, nil
+	}
+	thisV := *d
+	var otherV DUint32
+	switch t := other.(type) {
+	case *DUint32:
+		otherV = *t
+	}
+	if thisV < otherV {
+		return -1, nil
+	}
+	if thisV > otherV {
+		return 1, nil
+	}
+	return 0, nil
+}