/*
    * 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));
   }
 }