dragon warrior checksum?

    uint8_t cl = 0x1D, ch = 0x1D, carry = 0;
    uint8_t al, bl, temp;

	for (int i = len; i >=0; --i){
		al = data[i];
        for (int j = 8; j > 0; --j) {

            bl = al ^ ch;
			//printf("BL %02x | CH %02x \n", al, ch);

            carry = (cl & 0x80) ? 1 : 0;
            cl <<= 1;

            temp = (ch & 0x80) ? 1 : 0;
            ch = (ch << 1) | carry;
            carry = temp;

            carry = (al & 0x80) ? 1 : 0;
            al <<= 1;

            carry = (bl & 0x80) ? 1 : 0;
            bl <<= 1;

            if (carry) {
                cl ^= 0x21;
                ch ^= 0x10;
            }
        }
    }