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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 2008 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;

import static com.google.common.base.Preconditions.checkState;
import static java.nio.charset.StandardCharsets.UTF_8;

import com.google.common.base.CaseFormat;
import com.google.common.base.Strings;
import com.google.javascript.jscomp.JsMessage.IdGenerator;
import com.google.javascript.jscomp.JsMessage.PlaceholderReference;
import java.util.List;

/**
 * An {@link IdGenerator} designed to play nicely with Google's Translation
 * systems. Each message is scoped to a project id, so that it does
 * not conflict with other messages at Google.
 * 
 * Just as reminder what key type used in different formats:
 * 

 * XMB - id. We export using this format.
 * 
XTB - id. Internal, result of translation.
 * 
XLB - name. External, use it if we need to share translation with third
 *     part.
 * 
PROPERTIES - name.
 * 
 *
 * @see xmb
 */
public final class GoogleJsMessageIdGenerator implements IdGenerator {

  private final String projectId;

  /**
   * Creates an instance.
   *
   * @param projectId A TC project name (e.g. "MyProject")
   */
  public GoogleJsMessageIdGenerator(String projectId) {
    this.projectId = projectId;
  }

  @Override
  public String generateId(String meaning, List messageParts) {
    checkState(meaning != null);

    StringBuilder sb = new StringBuilder();
    for (CharSequence part : messageParts) {
      if (part instanceof PlaceholderReference) {
        sb.append(CaseFormat.LOWER_CAMEL.to(
            CaseFormat.UPPER_UNDERSCORE,
            ((PlaceholderReference) part).getName()));
      } else {
        sb.append(part);
      }
    }
    String tcValue = sb.toString();

    String projectScopedMeaning =
        (Strings.isNullOrEmpty(projectId) ? "" : (projectId + ": ")) + meaning;
    return String.valueOf(
        MessageId.generateId(tcValue, projectScopedMeaning));
  }


  /**
   * 64-bit fingerprint support.
   *
   * Forked from the guava-internal library.
   */
  private static final class FP {
    private FP() {}

    /** Generate fingerprint of "byte[start,limit-1]". */
    private static long fingerprint(byte[] str, int start, int limit) {
      int hi = hash32(str, start, limit, 0);
      int lo = hash32(str, start, limit, 102072);
      if ((hi == 0) && (lo == 0 || lo == 1)) {
        // Turn 0/1 into another fingerprint
        hi ^= 0x130f9bef;
        lo ^= 0x94a0a928;
      }
      return (((long) hi) << 32) | (lo & 0xffffffffL);
    }

    /**
     * Generate fingerprint of "str". Equivalent to UTF-encoding "str" into
     * bytes and then fingerprinting those bytes.
     */
    private static long fingerprint(String str) {
      byte[] tmp = str.getBytes(UTF_8);
      return FP.fingerprint(tmp, 0, tmp.length);
    }

    @SuppressWarnings("fallthrough")
    private static int hash32(byte[] str, int start, int limit, int c) {
      int a = 0x9e3779b9;
      int b = 0x9e3779b9;
      int i;
      for (i = start; i + 12 <= limit; i += 12) {
        a += (((str[i + 0] & 0xff) << 0)
            | ((str[i + 1] & 0xff) << 8)
            | ((str[i + 2] & 0xff) << 16)
            | ((str[i + 3] & 0xff) << 24));
        b += (((str[i + 4] & 0xff) << 0)
            | ((str[i + 5] & 0xff) << 8)
            | ((str[i + 6] & 0xff) << 16)
            | ((str[i + 7] & 0xff) << 24));
        c += (((str[i + 8] & 0xff) << 0)
            | ((str[i + 9] & 0xff) << 8) | ((str[i + 10] & 0xff) << 16)
            | ((str[i + 11] & 0xff) << 24));

        // Mix
        a -= b;
        a -= c;
        a ^= (c >>> 13);
        b -= c;
        b -= a;
        b ^= (a << 8);
        c -= a;
        c -= b;
        c ^= (b >>> 13);
        a -= b;
        a -= c;
        a ^= (c >>> 12);
        b -= c;
        b -= a;
        b ^= (a << 16);
        c -= a;
        c -= b;
        c ^= (b >>> 5);
        a -= b;
        a -= c;
        a ^= (c >>> 3);
        b -= c;
        b -= a;
        b ^= (a << 10);
        c -= a;
        c -= b;
        c ^= (b >>> 15);
      }

      c += limit - start;
      int tmp = limit - i;
      if (tmp == 11) {
        c += (str[i + 10] & 0xff) << 24;
      }
      if (tmp >= 10) {
        c += (str[i + 9] & 0xff) << 16;
      }
      if (tmp >= 9) {
        c += (str[i + 8] & 0xff) << 8;
        // the first byte of c is reserved for the length
      }
      if (tmp >= 8) {
        b += (str[i + 7] & 0xff) << 24;
      }
      if (tmp >= 7) {
        b += (str[i + 6] & 0xff) << 16;
      }
      if (tmp >= 6) {
        b += (str[i + 5] & 0xff) << 8;
      }
      if (tmp >= 5) {
        b += (str[i + 4] & 0xff);
      }
      if (tmp >= 4) {
        a += (str[i + 3] & 0xff) << 24;
      }
      if (tmp >= 3) {
        a += (str[i + 2] & 0xff) << 16;
      }
      if (tmp >= 2) {
        a += (str[i + 1] & 0xff) << 8;
      }
      if (tmp >= 1) {
        a += (str[i + 0] & 0xff);
        // case 0 : nothing left to add
      }

      // Mix
      a -= b;
      a -= c;
      a ^= (c >>> 13);
      b -= c;
      b -= a;
      b ^= (a << 8);
      c -= a;
      c -= b;
      c ^= (b >>> 13);
      a -= b;
      a -= c;
      a ^= (c >>> 12);
      b -= c;
      b -= a;
      b ^= (a << 16);
      c -= a;
      c -= b;
      c ^= (b >>> 5);
      a -= b;
      a -= c;
      a ^= (c >>> 3);
      b -= c;
      b -= a;
      b ^= (a << 10);
      c -= a;
      c -= b;
      c ^= (b >>> 15);
      return c;
    }
  }

  /**
   * Generates fingerprint for an English message using the FP package.
   * This supersedes the message id generation using C fingerprint
   * functions and JNI.  This is slower than the C implementation (
   * we're talking about microseconds here) but it avoids using JNI and
   * shared libraries.
   *
   * Forked from the i18n library.
   */
  private static class MessageId {
    private static final long generateId(String message, String meaning) {
      long fp = FP.fingerprint(message);
      if (null != meaning && meaning.length() > 0) {
        // combine the fingerprints of message and meaning
        long fp2 = FP.fingerprint(meaning);
        fp = fp2 + (fp << 1) + (fp < 0 ? 1 : 0);
      }
      // To avoid negative ids we strip the high-order bit
      return fp & 0x7fffffffffffffffL;
    }
  }
}