---

yaml
---
r: 51173
b: refs/heads/try
c: df66e8d
h: refs/heads/master
i:
  51171: d99bc78
v: v3

Author: Kimundi

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: 5f13e9ccc2e3328d4cd8ca49f84e6840dd998346
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: f7a2371c176663d59062ec5158f39faecba45768
-refs/heads/try: 75d615d6f6d8fd8e931689106dfa22e4a6e662a2
+refs/heads/try: df66e8d4a197443c214e918a858208ecc38e9f1c
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c

branches/try/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);
+    }
+
 }