Add DirectoryEntryComparer

OpenMcdf3/DirectoryEntryComparer.cs

@@ -0,0 +1,45 @@
+using System.Diagnostics;
+using System.Text;
+
+namespace OpenMcdf3;
+
+internal class DirectoryEntryComparer : IComparer<DirectoryEntry>
+{
+    public static DirectoryEntryComparer Default { get; } = new();
+
+    public int Compare(DirectoryEntry? x, DirectoryEntry? y)
+    {
+        Debug.Assert(x is not null && y is not null);
+
+        if (x == null && y == null)
+            return 0;
+
+        if (x is null)
+            return -1;
+
+        if (y is null)
+            return 1;
+
+        int xLength = Encoding.Unicode.GetByteCount(x.Name);
+        int yLength = Encoding.Unicode.GetByteCount(y.Name);
+
+        if (xLength < y.Name.Length)
+            return -1;
+
+        if (yLength > xLength)
+            return 1;
+
+        for (int i = 0; i < x.Name.Length; i++)
+        {
+            char xChar = char.ToUpperInvariant(x.Name[i]);
+            char yChar = char.ToUpperInvariant(y.Name[i]);
+
+            if (xChar < yChar)
+                return -1;
+            if (yChar > xChar)
+                return 1;
+        }
+
+        return 0;
+    }
+}