2 files changed, 77 insertions, 0 deletions
diff --git a/lib/btrfs/btrfsprim/key.go b/lib/btrfs/btrfsprim/key.go
index 7a3cc5c..b07cc8c 100644
--- a/lib/btrfs/btrfsprim/key.go
+++ b/lib/btrfs/btrfsprim/key.go
@@ -64,8 +64,26 @@ func (key Key) Mm() Key {
 		key.Offset--
 	case key.ItemType > 0:
 		key.ItemType--
+		key.Offset = MaxOffset
 	case key.ObjectID > 0:
 		key.ObjectID--
+		key.ItemType = MAX_KEY
+		key.Offset = MaxOffset
+	}
+	return key
+}
+
+func (key Key) Pp() Key {
+	switch {
+	case key.Offset < MaxOffset:
+		key.Offset++
+	case key.ItemType < MAX_KEY:
+		key.ItemType++
+		key.Offset = 0
+	case key.ObjectID < MAX_OBJECTID:
+		key.ObjectID++
+		key.ItemType = 0
+		key.Offset = 0
 	}
 	return key
 }
diff --git a/lib/btrfs/btrfsprim/key_test.go b/lib/btrfs/btrfsprim/key_test.go
new file mode 100644
index 0000000..6274b43
--- /dev/null
+++ b/lib/btrfs/btrfsprim/key_test.go
@@ -0,0 +1,59 @@
+// Copyright (C) 2023  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package btrfsprim
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func k(objID ObjID, typ ItemType, offset uint64) Key {
+	return Key{
+		ObjectID: objID,
+		ItemType: typ,
+		Offset:   offset,
+	}
+}
+
+func eq(t *testing.T, act, exp Key) {
+	t.Helper()
+	assert.Equal(t, exp, act)
+}
+
+func ppEq(t *testing.T, in, exp Key) {
+	t.Helper()
+	eq(t, in.Pp(), exp)
+	if in != MaxKey {
+		eq(t, exp.Mm(), in)
+	}
+}
+
+func mmEq(t *testing.T, in, exp Key) {
+	t.Helper()
+	eq(t, in.Mm(), exp)
+	if in != (Key{}) {
+		eq(t, exp.Pp(), in)
+	}
+}
+
+func TestKey(t *testing.T) {
+	t.Parallel()
+
+	eq(t, MaxKey, k(18446744073709551615, 255, 18446744073709551615))
+
+	// pp
+	ppEq(t, k(0, 0, 0), k(0, 0, 1))
+	ppEq(t, k(0, 0, 18446744073709551615), k(0, 1, 0))
+	ppEq(t, k(0, 255, 0), k(0, 255, 1))
+	ppEq(t, k(0, 255, 18446744073709551615), k(1, 0, 0))
+	ppEq(t, MaxKey, k(18446744073709551615, 255, 18446744073709551615))
+
+	// mm
+	mmEq(t, MaxKey, k(18446744073709551615, 255, 18446744073709551614))
+	mmEq(t, k(18446744073709551615, 255, 0), k(18446744073709551615, 254, 18446744073709551615))
+	mmEq(t, k(18446744073709551615, 0, 0), k(18446744073709551614, 255, 18446744073709551615))
+	mmEq(t, k(0, 0, 0), k(0, 0, 0))
+}