Fix a bug in unicode-range serialization.

Author: SimonSapin

src/css-parsing-tests/component_value_list.json

@@ -380,8 +380,8 @@
     ["unicode-range", 1048576, 2097151], "?"
 ],
 
-"u+1-2 U+100000-2 U+1000000-2 U+10-200000", [
-    ["unicode-range", 1, 2], " ",
+"u+20-3F U+100000-2 U+1000000-2 U+10-200000", [
+    ["unicode-range", 32, 63], " ",
     ["unicode-range", 1048576, 2], " ",
     ["unicode-range", 1048576, 1048576], ["number", "0", 0, "integer"],
         ["number", "-2", -2, "integer"], " ",

src/serializer.rs

@@ -120,11 +120,13 @@ impl<'a> ToCss for Token<'a> {
             Token::UnicodeRange(start, end) => {
                 try!(dest.write_str("U+"));
                 let bits = cmp::min(start.trailing_zeros(), (!end).trailing_zeros());
-                if bits >= 4 && start >> bits == end >> bits {
-                    let question_marks = bits / 4;
-                    let common = start >> question_marks * 4;
-                    if common != 0 {
-                        try!(write!(dest, "{:X}", common));
+                let question_marks = bits / 4;
+                let bits = question_marks * 4;
+                let truncated_start = start >> bits;
+                let truncated_end = end >> bits;
+                if truncated_start == truncated_end {
+                    if truncated_start != 0 {
+                        try!(write!(dest, "{:X}", truncated_start));
                     }
                     for _ in (0..question_marks) {
                         try!(dest.write_str("?"));