metainfo/fileinfo.go | 27 +++++++++++++++++++++++++++
 metainfo/metainfo.go |  6 ------

diff --git a/metainfo/fileinfo.go b/metainfo/fileinfo.go
new file mode 100644
index 0000000000000000000000000000000000000000..ff2d563169c4e2765e2a882a6371750bcec61b4e
--- /dev/null
+++ b/metainfo/fileinfo.go
@@ -0,0 +1,27 @@
+package metainfo
+
+import "strings"
+
+// Information specific to a single file inside the MetaInfo structure.
+type FileInfo struct {
+	Length int64    `bencode:"length"`
+	Path   []string `bencode:"path"`
+}
+
+func (fi *FileInfo) DisplayPath(info *Info) string {
+	if info.IsDir() {
+		return strings.Join(fi.Path, "/")
+	} else {
+		return info.Name
+	}
+}
+
+func (me FileInfo) Offset(info *Info) (ret int64) {
+	for _, fi := range info.Files {
+		if me.DisplayPath(info) == fi.DisplayPath(info) {
+			return
+		}
+		ret += fi.Length
+	}
+	panic("not found")
+}
diff --git a/metainfo/metainfo.go b/metainfo/metainfo.go
index 96a64cbc0b4499bfca26818c51602cfafb2a4170..ea09cce517f9cfc86956bddf933be56c4ed5a706 100644
--- a/metainfo/metainfo.go
+++ b/metainfo/metainfo.go
@@ -20,12 +20,6 @@ 	Encoding     string        `bencode:"encoding,omitempty"`
 	URLList      interface{}   `bencode:"url-list,omitempty"`
 }
 
-// Information specific to a single file inside the MetaInfo structure.
-type FileInfo struct {
-	Length int64    `bencode:"length"`
-	Path   []string `bencode:"path"`
-}
-
 // Load a MetaInfo from an io.Reader. Returns a non-nil error in case of
 // failure.
 func Load(r io.Reader) (*MetaInfo, error) {