Simplify index calculation

src/test.cpp

@@ -516,12 +516,7 @@ private:
       self->nextToken();
       MUSTTAIL return keepGoing(self);
     }
-    // If the top of the stack is a terminal that doesn't match, reject
+    MUSTTAIL return table[self->stack.back()][self->currentToken](self);
-    if (self->stack.back() < T_PAST_END) {
-      return false;
-    }
-    MUSTTAIL return table[self->stack.back() - T_PAST_END][self->currentToken](
-        self);
   }
 
   PRESERVE_NONE static bool reject(Parser2 *) { return false; }
@@ -602,7 +597,137 @@ private:
   }
 
   // table[nonterminal][terminal]
-  static constexpr continuation table[N_PAST_END - T_PAST_END][T_PAST_END] = {
+  static constexpr continuation table[N_PAST_END][T_PAST_END] = {
+      /*T_INVALID*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_EOF*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_LBRACE*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_RBRACE*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_COMMA*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_ATOM*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_STRING*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_LBRACKET*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_RBRACKET*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
+      /*T_COLON*/
+      {
+          /*T_INVALID*/ reject,
+          /*T_EOF*/ reject,
+          /*T_LBRACE*/ reject,
+          /*T_RBRACE*/ reject,
+          /*T_COMMA*/ reject,
+          /*T_ATOM*/ reject,
+          /*T_STRING*/ reject,
+          /*T_LBRACKET*/ reject,
+          /*T_RBRACKET*/ reject,
+          /*T_COLON*/ reject,
+      },
       /*N_VALUE*/
       {
           /*T_INVALID*/ reject,
@@ -659,54 +784,69 @@ private:
 
   Symbol currentToken;
   const char *bufBefore;
-  Symbol nextToken() {
+  void nextToken() {
     maybeSkipWs();
     bufBefore = buf;
     if (len == 0) {
-      return currentToken = T_EOF;
+      currentToken = T_EOF;
+      return;
     }
     if (*buf == '{') {
       parseLiteral("{");
-      return currentToken = T_LBRACE;
+      currentToken = T_LBRACE;
+      return;
     } else if (*buf == '[') {
       parseLiteral("[");
-      return currentToken = T_LBRACKET;
+      currentToken = T_LBRACKET;
+      return;
     } else if (*buf == '}') {
       parseLiteral("}");
-      return currentToken = T_RBRACE;
+      currentToken = T_RBRACE;
+      return;
     } else if (*buf == ']') {
       parseLiteral("]");
-      return currentToken = T_RBRACKET;
+      currentToken = T_RBRACKET;
+      return;
     } else if (*buf == ':') {
       parseLiteral(":");
-      return currentToken = T_COLON;
+      currentToken = T_COLON;
+      return;
     } else if (*buf == ',') {
       parseLiteral(",");
-      return currentToken = T_COMMA;
+      currentToken = T_COMMA;
+      return;
     } else if (*buf == '"') {
       if (!parse_string()) {
-        return currentToken = T_INVALID;
+        currentToken = T_INVALID;
+        return;
       }
-      return currentToken = T_STRING;
+      currentToken = T_STRING;
+      return;
     } else if (*buf == 't') {
       if (!parseLiteral("true")) {
-        return currentToken = T_INVALID;
+        currentToken = T_INVALID;
+        return;
       }
-      return currentToken = T_ATOM;
+      currentToken = T_ATOM;
+      return;
     } else if (*buf == 'f') {
       if (!parseLiteral("false")) {
-        return currentToken = T_INVALID;
+        currentToken = T_INVALID;
+        return;
       }
     } else if (*buf == 'n') {
       if (!parseLiteral("null")) {
-        return currentToken = T_INVALID;
+        currentToken = T_INVALID;
+        return;
       }
     } else {
       if (!parse_number()) {
-        return currentToken = T_INVALID;
+        currentToken = T_INVALID;
+        return;
       }
     }
-    return currentToken = T_ATOM;
+    currentToken = T_ATOM;
+    return;
   }
 
   char *buf;
@@ -798,3 +938,15 @@ TEST_CASE("bench") {
     bench.doNotOptimizeAway(parser.parse());
   });
 }
+
+TEST_CASE("bench2") {
+  auto c = Callbacks{};
+  ankerl::nanobench::Bench bench;
+  bench.batch(json.size());
+  bench.unit("byte");
+  bench.run("parser2", [&]() {
+    auto copy = json;
+    Parser2 parser(copy.data(), copy.length(), &c, nullptr);
+    bench.doNotOptimizeAway(parser.parse());
+  });
+}