Class CRC32

classpath/java/util/zip/CRC32.java:13–69

package java.util.zip;

public class CRC32 {
  private static final int Polynomial = 0x04C11DB7;
  private static final int Width = 32;
  private static final int Top = 1 << (Width - 1);
  private static final int InitialRemainder = 0xFFFFFFFF;
  private static final long ResultXor = 0xFFFFFFFFL;

  private static final int[] table = new int[256];

  static {
    for (int dividend = 0; dividend < 256; ++ dividend) {
      int remainder = dividend << (Width - 8);
      for (int bit = 8; bit > 0; --bit) {
        remainder = ((remainder & Top) != 0)
          ? (remainder << 1) ^ Polynomial
          : (remainder << 1);
      }
      table[dividend] = remainder;
    }
  }

  private int remainder = InitialRemainder;

  public void reset() {
    remainder = InitialRemainder;
  }

  public void update(int b) {
    remainder = table[reflect(b, 8) ^ (remainder >>> (Width - 8))]
      ^ (remainder << 8);
  }

  public void update(byte[] array, int offset, int length) {
    for (int i = 0; i < length; ++i) {
      update(array[offset + i] & 0xFF);
    }
  }

  public void update(byte[] array) {
    update(array, 0, array.length);
  }

  public long getValue() {
    return (reflect(remainder, Width) ^ ResultXor) & 0xFFFFFFFFL;
  }

  private static int reflect(int x, int n) {
    int reflection = 0;
    for (int i = 0; i < n; ++i) {
      if ((x & 1) != 0) {
        reflection |= (1 << ((n - 1) - i));
      }
      x = (x >>> 1);
    }
    return reflection;
  }
}