diff options
| -rw-r--r-- | src/libcore/str/mod.rs | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs index 4584c26bebc..f033f50e59e 100644 --- a/src/libcore/str/mod.rs +++ b/src/libcore/str/mod.rs @@ -1892,7 +1892,10 @@ impl StrExt for str { #[inline] fn is_char_boundary(&self, index: usize) -> bool { - if index == self.len() { return true; } + // 0 and len are always ok. + // Test for 0 explicitly so that it can optimize out the check + // easily and skip reading string data for that case. + if index == 0 || index == self.len() { return true; } match self.as_bytes().get(index) { None => false, Some(&b) => b < 128 || b >= 192, |