This isn't AbleScript, we can just negate expressions :D

ablescript/src/base_55.rs

@@ -6,7 +6,7 @@ pub fn char2num(c: char) -> isize {
         '\\' => 54,
         '.' => 55,
         'U' => -210,
-        'A'..='Z' => 0 - (c as isize) + 64,
+        'A'..='Z' => -(c as isize) + 64,
         'a'..='z' => (c as isize) - 96,
         _ => 0,
     }