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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs.

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/*
 * Copyright 2011 The Closure Compiler Authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.javascript.jscomp.parsing.parser;

/** JS identifier parsing utilities. */
public final class Identifiers {

  @SuppressWarnings("ShortCircuitBoolean") // Intentional to minimize branches in this code
  public static boolean isIdentifierStart(char ch) {
    // Most code is written in pure ASCII, so create a fast path here.
    if (ch <= 127) {
      // Intentionally avoiding short circuiting behavior of "||" and "&&".
      // This minimizes branches in this code which minimizes branch prediction misses.
      return ((ch >= 'A' & ch <= 'Z') | (ch >= 'a' & ch <= 'z') | (ch == '_' | ch == '$'));
    }

    // Handle non-ASCII characters.
    // TODO(tjgq): This should include all characters with the ID_Start property.
    if (Character.isLetter(ch)) {
      return true;
    }

    // Workaround for b/36459436.
    // When running under GWT/J2CL, Character.isLetter only handles ASCII.
    // Angular relies heavily on Latin Small Letter Barred O and Greek Capital Letter Delta.
    // Greek letters are occasionally found in math code.
    // Latin letters are found in our own tests.
    return (ch >= 0x00C0 & ch <= 0x00D6) // Latin letters
        // 0x00D7 = multiplication sign, not a letter
        | (ch >= 0x00D8 & ch <= 0x00F6) // Latin letters
        // 0x00F7 = division sign, not a letter
        | (ch >= 0x00F8 & ch <= 0x00FF) // Latin letters
        | ch == 0x0275 // Latin Barred O
        | (ch >= 0x0391 & ch <= 0x03A1) // Greek uppercase letters
        // 0x03A2 = unassigned
        | (ch >= 0x03A3 & ch <= 0x03A9) // Remaining Greek uppercase letters
        | (ch >= 0x03B1 & ch <= 0x03C9); // Greek lowercase letters
  }

  @SuppressWarnings("ShortCircuitBoolean") // Intentional to minimize branches in this code
  public static boolean isIdentifierPart(char ch) {
    // Most code is written in pure ASCII, so create a fast path here.
    if (ch <= 127) {
      return ((ch >= 'A' & ch <= 'Z')
          | (ch >= 'a' & ch <= 'z')
          | (ch >= '0' & ch <= '9')
          | (ch == '_' | ch == '$'));
    }

    // Handle non-ASCII characters.
    // TODO(tjgq): This should include all characters with the ID_Continue property, plus
    // Zero Width Non-Joiner and Zero Width Joiner.
    return isIdentifierStart(ch) || Character.isDigit(ch);
  }

  private Identifiers() {}
}