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

Cargo.toml

@@ -37,7 +37,7 @@ version = "0.2.0"
 default-features = false
 
 [dependencies.memchr]
-version = "2.3"
+version = "2.4"
 default-features = false
 
 [dev-dependencies]

src/traits.rs

@@ -922,35 +922,7 @@ pub trait FindSubstring<T> {
 
 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)
  }
 }