NextionChecksum.py

"""
Nextion uses a CRC32 type algorithm.
"""


class Checksum:
    def CRC(self, data, salt: int = 0xffffffff, skip: int = 0, length: int = -1):
        if length < 0:
            length = len(data)
        data = data[skip:length]
        if type(data) is bytes:
            data = [int(b) for b in data]
        return self._CRC32(data, salt)

    def _CRC32(self, l: list, xorIn=0xffffffff, xorOut=0):
        poly = 0x4c11db7
        poly |= (1 << 32)  # kill the bit that would normally be shifted out of the register
        reg = 0
        l = l + [0]
        l[0] ^= xorIn
        for word in l:
            for i in range(32):
                reg <<= 1
                if word >= (1 << 31):
                    reg += 1
                word <<= 1
                word &= 0xffffffff
                if reg >= (1 << 32):
                    reg ^= poly
        reg &= 0xffffffff  # ((1 << 32) - 1)
        reg ^= xorOut
        return reg