Rollup merge of #141516 - bend-n:okay, r=workingjubilee

speed up charsearcher for ascii chars

attempt at fixing rust-lang/rust#82471

this implementation should be valid because ascii characters are always one byte and there are no continuation bytes that overlap with ascii characters

im not completely sure that this is _always_ an improvement but it seems to be an improvement for this case and i dont think it can significantly regress any cases

2 files changed, 32 insertions, 2 deletions

diff --git a/library/core/src/str/iter.rs b/library/core/src/str/iter.rs
index 425c4eaee28..49c581f352e 100644
--- a/library/core/src/str/iter.rs
+++ b/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;
diff --git a/library/core/src/str/pattern.rs b/library/core/src/str/pattern.rs
index bcbbb11c83b..e8189a2187b 100644
--- a/library/core/src/str/pattern.rs
+++ b/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 {
+            return match self
+                .haystack
+                .as_bytes()
+                .get(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 +513,21 @@ unsafe impl<'a> ReverseSearcher<'a> for CharSearcher<'a> {
     }
     #[inline]
     fn next_match_back(&mut self) -> Option<(usize, usize)> {
+        if self.utf8_size == 1 {
+            return match self
+                .haystack
+                .get(self.finger..self.finger_back)?
+                .as_bytes()
+                .iter()
+                .rposition(|&x| x == self.utf8_encoded[0])
+            {
+                Some(x) => {
+                    self.finger_back = self.finger + x;
+                    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