---

yaml
---
r: 50421
b: refs/heads/auto
c: df66e8d
h: refs/heads/master
i:
  50419: 8b303ac
v: v3

Author: Kimundi

[refs]

@@ -14,5 +14,5 @@ refs/heads/try3: 9387340aab40a73e8424c48fd42f0c521a4875c0
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: 75d615d6f6d8fd8e931689106dfa22e4a6e662a2
+refs/heads/auto: df66e8d4a197443c214e918a858208ecc38e9f1c
 refs/heads/servo: af82457af293e2a842ba6b7759b70288da276167

branches/auto/src/libcore/str.rs

@@ -1865,8 +1865,10 @@ pub struct CharRange {
  * Given a byte position and a str, return the previous char and its position
  *
  * This function can be used to iterate over a unicode string in reverse.
+ *
+ * returns 0 for next index if called on start index 0
  */
-fn char_range_at_reverse(ss: &str, start: uint) -> CharRange {
+pub fn char_range_at_reverse(ss: &str, start: uint) -> CharRange {
     let mut prev = start;
 
     // while there is a previous byte == 10......
@@ -1875,7 +1877,12 @@ fn char_range_at_reverse(ss: &str, start: uint) -> CharRange {
     }
 
     // now refer to the initial byte of previous char
-    prev -= 1u;
+    if prev > 0u {
+        prev -= 1u;
+    } else {
+        prev = 0u;
+    }
+
 
     let ch = char_at(ss, prev);
     return CharRange {ch:ch, next:prev};
@@ -3761,4 +3768,10 @@ mod tests {
         "12345555".cmp(& &"123456") == Less;
         "22".cmp(& &"1234") == Greater;
     }
+
+    #[test]
+    fn test_char_range_at_reverse_underflow() {
+        assert!(char_range_at_reverse("abc", 0).next == 0);
+    }
+
 }