Java example source code file (Crc32cHashFunctionTest.java)

This example Java source code file (Crc32cHashFunctionTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

crc32c_generator_flipped, crc32chashfunctiontest, expected, testcase, the, util

The Crc32cHashFunctionTest.java Java example source code

/*
 * Copyright (C) 2011 The Guava 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.common.hash;

import static com.google.common.base.Charsets.UTF_8;

import junit.framework.TestCase;

import java.util.Arrays;

/**
 * Unit tests for {@link Crc32c}. Known test values are from RFC 3720, Section B.4.
 *
 * @author Patrick Costello
 * @author Kurt Alfred Kluever
 */
public class Crc32cHashFunctionTest extends TestCase {

  public void testZeros() {
    // Test 32 byte array of 0x00.
    byte[] zeros = new byte[32];
    Arrays.fill(zeros, (byte) 0x00);
    assertCrc(0x8a9136aa, zeros);
  }

  public void testFull() {
    // Test 32 byte array of 0xFF.
    byte[] fulls = new byte[32];
    Arrays.fill(fulls, (byte) 0xFF);
    assertCrc(0x62a8ab43, fulls);
  }

  public void testAscending() {
    // Test 32 byte arrays of ascending.
    byte[] ascending = new byte[32];
    for (int i = 0; i < 32; i++) {
      ascending[i] = (byte) i;
    }
    assertCrc(0x46dd794e, ascending);
  }

  public void testDescending() {
    // Test 32 byte arrays of descending.
    byte[] descending = new byte[32];
    for (int i = 0; i < 32; i++) {
      descending[i] = (byte) (31 - i);
    }
    assertCrc(0x113fdb5c, descending);
  }

  public void testScsiReadCommad() {
    // Test SCSI read command.
    byte[] scsiReadCommand = new byte[] {
        0x01, (byte) 0xc0, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00,
        0x14, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x04, 0x00,
        0x00, 0x00, 0x00, 0x14,
        0x00, 0x00, 0x00, 0x18,
        0x28, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00,
        0x02, 0x00, 0x00, 0x00,
        0x00, 0x00, 0x00, 0x00 };
    assertCrc(0xd9963a56, scsiReadCommand);
  }

  // Known values from http://www.evanjones.ca/crc32c.html
  public void testSomeOtherKnownValues() {
    assertCrc(0x22620404, "The quick brown fox jumps over the lazy dog".getBytes(UTF_8));
    assertCrc(0xE3069283, "123456789".getBytes(UTF_8));
    assertCrc(0xf3dbd4fe, "1234567890".getBytes(UTF_8));
    assertCrc(0xBFE92A83, "23456789".getBytes(UTF_8));
  }

  /**
   * Verfies that the crc of an array of byte data matches the expected value.
   *
   * @param expectedCrc the expected crc value.
   * @param data the data to run the checksum on.
   */
  private static void assertCrc(int expectedCrc, byte[] data) {
    int actualCrc = Hashing.crc32c().hashBytes(data).asInt();
    assertEquals(expectedCrc, actualCrc);
  }

  // From RFC 3720, Section 12.1, the polynomial generator is 0x11EDC6F41.
  // We calculate the constant below by:
  //   1. Omitting the most significant bit (because it's always 1). => 0x1EDC6F41
  //   2. Flipping the bits of the constant so we can process a byte at a time. => 0x82F63B78
  private static final int CRC32C_GENERATOR = 0x1EDC6F41;  // 0x11EDC6F41
  private static final int CRC32C_GENERATOR_FLIPPED = Integer.reverse(CRC32C_GENERATOR);

  public void testCrc32cLookupTable() {
    // See Hacker's Delight 2nd Edition, Figure 14-7.
    int[] expected = new int[256];
    for (int i = 0; i < expected.length; i++) {
      int crc = i;
      for (int j = 7; j >= 0; j--) {
        int mask = -(crc & 1);
        crc = ((crc >>> 1) ^ (CRC32C_GENERATOR_FLIPPED & mask));
      }
      expected[i] = crc;
    }

    int[] actual = Crc32cHashFunction.Crc32cHasher.CRC_TABLE;
    assertTrue(
        "Expected: \n" + Arrays.toString(expected) + "\nActual:\n" + Arrays.toString(actual),
        Arrays.equals(expected, actual));
  }
}