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 
17 package com.google.clearsilver.jsilver.functions.string;
18 
19 import com.google.clearsilver.jsilver.functions.NonEscapingFunction;
20 import com.google.clearsilver.jsilver.values.Value;
21 import static com.google.clearsilver.jsilver.values.Value.literalConstant;
22 
23 import java.io.UnsupportedEncodingException;
24 import java.util.zip.CRC32;
25 import java.util.zip.Checksum;
26 
27 /**
28  * Returns the CRC-32 of a string.
29  */
30 public class CrcFunction extends NonEscapingFunction {
31 
32   /**
33    * @param args 1 string expression
34    * @return CRC-32 of string as number value
35    */
execute(Value... args)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