1 files changed, 42 insertions, 0 deletions
diff --git a/format/commitgraph/generation.go b/format/commitgraph/generation.go
new file mode 100644
index 00000000..41c743ab
--- /dev/null
+++ b/format/commitgraph/generation.go
@@ -0,0 +1,42 @@
+package commitgraph
+
+import (
+	"encoding/binary"
+
+	"codeberg.org/lindenii/furgit/internal/intconv"
+)
+
+func (reader *Reader) readGenerationV2(layer *layer, index uint32, commitTime uint64) (uint64, error) {
+	if len(layer.chunkGeneration) == 0 {
+		return 0, nil
+	}
+
+	off64 := uint64(index) * 4
+
+	off, err := intconv.Uint64ToInt(off64)
+	if err != nil {
+		return 0, err
+	}
+
+	value := binary.BigEndian.Uint32(layer.chunkGeneration[off : off+4])
+
+	if value&generationOverflow == 0 {
+		return commitTime + uint64(value), nil
+	}
+
+	gdo2Index := value ^ generationOverflow
+	gdo2Off64 := uint64(gdo2Index) * 8
+
+	gdo2Off, err := intconv.Uint64ToInt(gdo2Off64)
+	if err != nil {
+		return 0, err
+	}
+
+	if gdo2Off+8 > len(layer.chunkGenerationOv) {
+		return 0, &ErrMalformed{Path: layer.path, Reason: "GDO2 index out of range"}
+	}
+
+	overflow := binary.BigEndian.Uint64(layer.chunkGenerationOv[gdo2Off : gdo2Off+8])
+
+	return commitTime + overflow, nil
+}