Gadgetbridge/app/src/main/java/nodomain/freeyourgadget/gadgetbridge/util/CheckSums.java

package nodomain.freeyourgadget.gadgetbridge.util;

public class CheckSums {
    public static int getCRC8(byte[] seq) {
        int len = seq.length;
        int i = 0;
        byte crc = 0x00;

        while (len-- > 0) {
            byte extract = seq[i++];
            for (byte tempI = 8; tempI != 0; tempI--) {
                byte sum = (byte) ((crc & 0xff) ^ (extract & 0xff));
                sum = (byte) ((sum & 0xff) & 0x01);
                crc = (byte) ((crc & 0xff) >>> 1);
                if (sum != 0) {
                    crc = (byte) ((crc & 0xff) ^ 0x8c);
                }
                extract = (byte) ((extract & 0xff) >>> 1);
            }
        }
        return (crc & 0xff);
    }

    //thanks http://stackoverflow.com/questions/13209364/convert-c-crc16-to-java-crc16
    public static int getCRC16(byte[] seq) {
        int crc = 0xFFFF;

        for (int j = 0; j < seq.length; j++) {
            crc = ((crc >>> 8) | (crc << 8)) & 0xffff;
            crc ^= (seq[j] & 0xff);//byte to int, trunc sign
            crc ^= ((crc & 0xff) >> 4);
            crc ^= (crc << 12) & 0xffff;
            crc ^= ((crc & 0xFF) << 5) & 0xffff;
        }
        crc &= 0xffff;
        return crc;
    }
}