1 files changed, 26 insertions, 0 deletions
diff --git a/format/packfile/ofs.go b/format/packfile/ofs.go
new file mode 100644
index 00000000..4992a506
--- /dev/null
+++ b/format/packfile/ofs.go
@@ -0,0 +1,26 @@
+package packfile
+
+import "fmt"
+
+// ParseOfsDeltaDistance parses one ofs-delta backward distance.
+func ParseOfsDeltaDistance(buf []byte) (uint64, int, error) {
+	if len(buf) == 0 {
+		return 0, 0, fmt.Errorf("packfile: malformed ofs-delta distance")
+	}
+
+	b := buf[0]
+	dist := uint64(b & 0x7f)
+
+	consumed := 1
+	for b&0x80 != 0 {
+		if consumed >= len(buf) {
+			return 0, 0, fmt.Errorf("packfile: malformed ofs-delta distance")
+		}
+
+		b = buf[consumed]
+		consumed++
+		dist = ((dist + 1) << 7) + uint64(b&0x7f)
+	}
+
+	return dist, consumed, nil
+}