Merge pull request #319 from epage/perf2

perf: Backport 0.5 improvements

src/error.rs

@@ -260,13 +260,13 @@ impl<E> ErrMode<E> {
 }
 
 impl<I, E: ParseError<I>> ParseError<I> for ErrMode<E> {
-    #[inline]
+    #[inline(always)]
     fn from_error_kind(input: I, kind: ErrorKind) -> Self {
         ErrMode::Backtrack(E::from_error_kind(input, kind))
     }
 
     #[cfg_attr(debug_assertions, track_caller)]
-    #[inline]
+    #[inline(always)]
     fn assert(input: I, message: &'static str) -> Self
     where
         I: crate::lib::std::fmt::Debug,
@@ -295,7 +295,7 @@ impl<I, EXT, E> FromExternalError<I, EXT> for ErrMode<E>
 where
     E: FromExternalError<I, EXT>,
 {
-    #[inline]
+    #[inline(always)]
     fn from_external_error(input: I, kind: ErrorKind, e: EXT) -> Self {
         ErrMode::Backtrack(E::from_external_error(input, kind, e))
     }

src/stream/mod.rs

@@ -2636,7 +2636,35 @@ fn memchr(token: u8, slice: &[u8]) -> Option<usize> {
 #[cfg(feature = "simd")]
 #[inline(always)]
 fn memmem(slice: &[u8], tag: &[u8]) -> Option<usize> {
-    memchr::memmem::find(slice, tag)
+    if tag.len() > slice.len() {
+        return None;
+    }
+
+    let (&substr_first, substr_rest) = match tag.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, slice);
+    }
+
+    let mut offset = 0;
+    let haystack = &slice[..slice.len() - substr_rest.len()];
+
+    while let Some(position) = memchr::memchr(substr_first, &haystack[offset..]) {
+        offset += position;
+        let next_offset = offset + 1;
+        if &slice[next_offset..][..substr_rest.len()] == substr_rest {
+            return Some(offset);
+        }
+
+        offset = next_offset;
+    }
+
+    None
 }
 
 #[cfg(not(feature = "simd"))]