Skip linear search over DAFSA node children at first layer

Signed-off-by: Simon Wülker <[email protected]>

Author: simonwuelker

html5ever/src/tokenizer/char_ref/codegen.rs

@@ -114,3 +114,16 @@ pub(crate) fn resolve_unique_hash_value(value: usize) -> CharRef {
         num_chars,
     }
 }
+
+pub(crate) fn compute_index_of_first_character(c: char) -> Option<usize> {
+    debug_assert!(c.is_ascii_alphabetic());
+
+    let index = c as u32 as u8;
+    if c.is_ascii_uppercase() {
+        Some((index - b'A') as usize)
+    } else if c.is_ascii_lowercase() {
+        Some((index - b'a') as usize)
+    } else {
+        None
+    }
+}

html5ever/src/tokenizer/char_ref/named.rs

@@ -9,6 +9,7 @@
 
 use super::codegen::{resolve_unique_hash_value, Node, DAFSA_NODES};
 use super::{CharRef, Status};
+use crate::tokenizer::char_ref::codegen::compute_index_of_first_character;
 use crate::tokenizer::TokenSink;
 use crate::tokenizer::Tokenizer;
 use markup5ever::buffer_queue::BufferQueue;
@@ -121,6 +122,23 @@ impl NamedReferenceTokenizerState {
         tokenizer: &Tokenizer<Sink>,
         input: &BufferQueue,
     ) -> Result<Status, StrTendril> {
+        // Optimization: If this is the first character in the named reference then
+        // we know the index of the child node, and we also know that we can't possibly be done yet.
+        // This saves us from having to do a linear search over all children of the root node.
+        if !self.has_consumed_characters() {
+            let Some(c) = tokenizer.peek(input) else {
+                return Ok(Status::Stuck);
+            };
+            tokenizer.discard_char(input);
+            self.name_buffer.push_char(c);
+            let Some(first_index) = compute_index_of_first_character(c) else {
+                // First character not in the range a-z or A-Z
+                return Err(mem::take(&mut self.name_buffer));
+            };
+
+            self.current_node = &DAFSA_NODES[first_index];
+        }
+
         loop {
             let Some(c) = tokenizer.peek(input) else {
                 return Ok(Status::Stuck);
@@ -196,6 +214,10 @@ impl NamedReferenceTokenizerState {
         }
         char_ref
     }
+
+    fn has_consumed_characters(&self) -> bool {
+        !self.name_buffer.is_empty() || !self.last_match.is_none()
+    }
 }
 
 pub(crate) fn emit_name_error<Sink: TokenSink>(name: StrTendril, tokenizer: &Tokenizer<Sink>) {