CrcFunction.java revision 712c262ddf6790c16a8567053f616c71da7e1856 
1/*
2 * Copyright (C) 2010 Google Inc.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.clearsilver.jsilver.functions.string;
18
19import com.google.clearsilver.jsilver.functions.NonEscapingFunction;
20import com.google.clearsilver.jsilver.values.Value;
21import static com.google.clearsilver.jsilver.values.Value.literalConstant;
22
23import java.io.UnsupportedEncodingException;
24import java.util.zip.CRC32;
25import java.util.zip.Checksum;
26
27/**
28 * Returns the CRC-32 of a string.
29 */
30public class CrcFunction extends NonEscapingFunction {
31
32  /**
33   * @param args 1 string expression
34   * @return CRC-32 of string as number value
35   */
36  public Value execute(Value... args) {
37    String string = args[0].asString();
38    // This function produces a 'standard' CRC-32 (IV -1, reflected polynomial,
39    // and final complement step). The CRC-32 of "123456789" is 0xCBF43926.
40    Checksum crc = new CRC32();
41    byte[] b;
42    try {
43      b = string.getBytes("UTF-8");
44    } catch (UnsupportedEncodingException e) {
45      throw new AssertionError("UTF-8 must be supported");
46    }
47    crc.update(b, 0, b.length);
48    // Note that we need to cast to signed int, but that's okay because the
49    // CRC fits into 32 bits by definition.
50    return literalConstant((int) crc.getValue(), args[0]);
51  }
52}
53