internal: improve TokenSet implementation

Author: davidsemakula

crates/parser/src/token_set.rs

@@ -4,32 +4,46 @@ use crate::SyntaxKind;
 
 /// A bit-set of `SyntaxKind`s
 #[derive(Clone, Copy)]
-pub(crate) struct TokenSet(u128);
+pub(crate) struct TokenSet([u64; 3]);
+
+const LAST_TOKEN_KIND_DISCRIMINANT: usize = SyntaxKind::SHEBANG as usize;
 
 impl TokenSet {
-    pub(crate) const EMPTY: TokenSet = TokenSet(0);
+    pub(crate) const EMPTY: TokenSet = TokenSet([0; 3]);
 
     pub(crate) const fn new(kinds: &[SyntaxKind]) -> TokenSet {
-        let mut res = 0u128;
+        let mut res = [0; 3];
         let mut i = 0;
         while i < kinds.len() {
-            res |= mask(kinds[i]);
+            let kind = kinds[i];
+            debug_assert!(
+                kind as usize <= LAST_TOKEN_KIND_DISCRIMINANT,
+                "Expected a token `SyntaxKind`"
+            );
+            let idx = kind as usize / 64;
+            res[idx] |= mask(kind);
             i += 1;
         }
         TokenSet(res)
     }
 
     pub(crate) const fn union(self, other: TokenSet) -> TokenSet {
-        TokenSet(self.0 | other.0)
+        TokenSet([self.0[0] | other.0[0], self.0[1] | other.0[1], self.0[2] | other.0[2]])
     }
 
     pub(crate) const fn contains(&self, kind: SyntaxKind) -> bool {
-        self.0 & mask(kind) != 0
+        debug_assert!(
+            kind as usize <= LAST_TOKEN_KIND_DISCRIMINANT,
+            "Expected a token `SyntaxKind`"
+        );
+        let idx = kind as usize / 64;
+        self.0[idx] & mask(kind) != 0
     }
 }
 
-const fn mask(kind: SyntaxKind) -> u128 {
-    1u128 << (kind as usize)
+const fn mask(kind: SyntaxKind) -> u64 {
+    debug_assert!(kind as usize <= LAST_TOKEN_KIND_DISCRIMINANT, "Expected a token `SyntaxKind`");
+    1 << (kind as usize % 64)
 }
 
 #[test]