Rollup merge of rust-lang#70046 - lzutao:patch-1, r=Centril

Use sublice patterns to avoid computing the len r? @Centril
Centril · Mar 16, 2020 · 9a9c6d8 · 9a9c6d8
2 parents 2bc6c0e + e1bc9af
commit 9a9c6d8
Showing 1 changed file with 4 additions and 12 deletions.
diff --git a/src/libstd/sys_common/wtf8.rs b/src/libstd/sys_common/wtf8.rs
@@ -599,24 +599,16 @@ impl Wtf8 {
 
     #[inline]
     fn final_lead_surrogate(&self) -> Option<u16> {
-        let len = self.len();
-        if len < 3 {
-            return None;
-        }
-        match self.bytes[(len - 3)..] {
-            [0xED, b2 @ 0xA0..=0xAF, b3] => Some(decode_surrogate(b2, b3)),
+        match self.bytes {
+            [.., 0xED, b2 @ 0xA0..=0xAF, b3] => Some(decode_surrogate(b2, b3)),
             _ => None,
         }
     }
 
     #[inline]
     fn initial_trail_surrogate(&self) -> Option<u16> {
-        let len = self.len();
-        if len < 3 {
-            return None;
-        }
-        match self.bytes[..3] {
-            [0xED, b2 @ 0xB0..=0xBF, b3] => Some(decode_surrogate(b2, b3)),
+        match self.bytes {
+            [0xED, b2 @ 0xB0..=0xBF, b3, ..] => Some(decode_surrogate(b2, b3)),
             _ => None,
         }
     }