package oop.frame.structure;

public class CRC32 {

private int crc
= 0xFFFFFFFF;
// initial contents
/**
* calculates a checksum for given input {@code byte[]}
* @param bytes {@code byte[]} to create checksum for
*/
public void update(byte[] bytes) {
int poly = 0xEDB88320;
// reverse polynomial
for (byte b : bytes) {
int temp = (crc ^ b) & 0xff;
// read 8 bits one at a time
for (int i = 0; i < 8; i++) {
if ((temp & 1) == 1) {
temp = (temp >>> 1) ^ poly;
} else {
temp = (temp >>> 1);
}
}
crc = (crc >>> 8) ^ temp;
}
// flip bits
crc = crc ^ 0xffffffff;
}
/**
* Gets the calculated checksum
* @return {@code byte[]} representing the checksum
*/
public byte[] getCRC() {
return new byte[] {
(byte) (crc >> 24),
(byte) (crc >> 16),
(byte) (crc >> 8),
(byte) crc};
}
}