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  • Denis Shuvalov thinks this is interesting:

import java.util.zip.*;
public class ParityChecksum implements Checksum {
  private long checksum = 0;
  public void update(int b) {
    int numOneBits = 0;
    for (int i = 1; i < 256; i *= 2) {
      if ((b & i) != 0) numOneBits++;
    }
    checksum = (checksum + numOneBits) % 2;
  }
  public void update(byte data[], int offset, int length) {
    for (int i = offset; i < offset+length; i++) {
      this.update(data[i]);
    }
  }

  public long getValue( ) {
    return checksum;
  }
  public void reset( ) {
    checksum = 0;
  }
}

From

Cover of Java I/O, 2nd Edition

Note

looks like a bug, should be only length