increase perf of charsearcher for single ascii characters

Author: bend-n

library/core/src/str/iter.rs

@@ -656,7 +656,7 @@ impl<'a, P: Pattern> SplitInternal<'a, P> {
         None
     }
 
-    #[inline]
+    #[inline(always)]
     fn next(&mut self) -> Option<&'a str> {
         if self.finished {
             return None;

library/core/src/str/pattern.rs

@@ -429,8 +429,23 @@ unsafe impl<'a> Searcher<'a> for CharSearcher<'a> {
             SearchStep::Done
         }
     }
-    #[inline]
+    #[inline(always)]
     fn next_match(&mut self) -> Option<(usize, usize)> {
+        if self.utf8_size == 1 {
+            // SAFETY: invariant
+            return match unsafe {
+                self.haystack.as_bytes().get_unchecked(self.finger..self.finger_back)
+            }
+            .iter()
+            .position(|x| *x == self.utf8_encoded[0])
+            {
+                Some(x) => {
+                    self.finger += x + 1;
+                    Some((self.finger - 1, self.finger))
+                }
+                None => None,
+            };
+        }
         loop {
             // get the haystack after the last character found
             let bytes = self.haystack.as_bytes().get(self.finger..self.finger_back)?;
@@ -498,6 +513,23 @@ unsafe impl<'a> ReverseSearcher<'a> for CharSearcher<'a> {
     }
     #[inline]
     fn next_match_back(&mut self) -> Option<(usize, usize)> {
+        if self.utf8_size == 1 {
+            // SAFETY: invariant
+            return match unsafe {
+                self.haystack
+                    .get_unchecked(self.finger..self.finger_back)
+                    .as_bytes()
+                    .iter()
+                    .rposition(|&x| x == self.utf8_encoded[0])
+            } {
+                Some(x) => {
+                    let index = self.finger + x;
+                    self.finger_back = index;
+                    Some((self.finger_back, self.finger_back + 1))
+                }
+                None => None,
+            };
+        }
         let haystack = self.haystack.as_bytes();
         loop {
             // get the haystack up to but not including the last character searched