Compressing Streams: Parity Checksum

         

import java.util.zip.Checksum;

public class ParityChecksum implements Checksum {
  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;
  }
}

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Compressing Streams: Parity Checksum : Zip Tar File « File Input Output « Java

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