FindSubstring<&[u8]>: make use of memchr::memmem

src/input.rs

@@ -2247,35 +2247,7 @@ where
 
 impl<'a, 'b> FindSubstring<&'b [u8]> for &'a [u8] {
   fn find_substring(&self, substr: &'b [u8]) -> Option<usize> {
-    if substr.len() > self.len() {
-      return None;
-    }
-
-    let (&substr_first, substr_rest) = match substr.split_first() {
-      Some(split) => split,
-      // an empty substring is found at position 0
-      // This matches the behavior of str.find("").
-      None => return Some(0),
-    };
-
-    if substr_rest.is_empty() {
-      return memchr::memchr(substr_first, self);
-    }
-
-    let mut offset = 0;
-    let haystack = &self[..self.len() - substr_rest.len()];
-
-    while let Some(position) = memchr::memchr(substr_first, &haystack[offset..]) {
-      offset += position;
-      let next_offset = offset + 1;
-      if &self[next_offset..][..substr_rest.len()] == substr_rest {
-        return Some(offset);
-      }
-
-      offset = next_offset;
-    }
-
-    None
+    memchr::memmem::find(self, substr)
   }
 }