Issue #14874: Restore charmap decoding speed to pre-PEP 393 levels.
Patch by Serhiy Storchaka.
diff --git a/Lib/encodings/cp037.py b/Lib/encodings/cp037.py
index 4edd708..bfe2c1e 100644
--- a/Lib/encodings/cp037.py
+++ b/Lib/encodings/cp037.py
@@ -301,6 +301,7 @@
     '\xd9'     #  0xFD -> LATIN CAPITAL LETTER U WITH GRAVE
     '\xda'     #  0xFE -> LATIN CAPITAL LETTER U WITH ACUTE
     '\x9f'     #  0xFF -> CONTROL
+    '\ufffe'   ## Widen to UCS2 for optimization
 )
 
 ### Encoding table