crc.py

import sys

__author__ = "Nicco Kunzmann"
__version__ = "0.1.0"

PY2 = sys.version_info[0] == 2


class crc8(object):
    digest_size = 1
    block_size = 1

    _table = [0x00, 0xD5, 0x7F, 0xAA, 0xFE, 0x2B, 0x81, 0x54, 0x29, 0xFC, 0x56, 0x83, 0xD7, 0x02, 0xA8, 0x7D,
           0x52, 0x87, 0x2D, 0xF8, 0xAC, 0x79, 0xD3, 0x06, 0x7B, 0xAE, 0x04, 0xD1, 0x85, 0x50, 0xFA, 0x2F,
           0xA4, 0x71, 0xDB, 0x0E, 0x5A, 0x8F, 0x25, 0xF0, 0x8D, 0x58, 0xF2, 0x27, 0x73, 0xA6, 0x0C, 0xD9,
           0xF6, 0x23, 0x89, 0x5C, 0x08, 0xDD, 0x77, 0xA2, 0xDF, 0x0A, 0xA0, 0x75, 0x21, 0xF4, 0x5E, 0x8B,
           0x9D, 0x48, 0xE2, 0x37, 0x63, 0xB6, 0x1C, 0xC9, 0xB4, 0x61, 0xCB, 0x1E, 0x4A, 0x9F, 0x35, 0xE0,
           0xCF, 0x1A, 0xB0, 0x65, 0x31, 0xE4, 0x4E, 0x9B, 0xE6, 0x33, 0x99, 0x4C, 0x18, 0xCD, 0x67, 0xB2,
           0x39, 0xEC, 0x46, 0x93, 0xC7, 0x12, 0xB8, 0x6D, 0x10, 0xC5, 0x6F, 0xBA, 0xEE, 0x3B, 0x91, 0x44,
           0x6B, 0xBE, 0x14, 0xC1, 0x95, 0x40, 0xEA, 0x3F, 0x42, 0x97, 0x3D, 0xE8, 0xBC, 0x69, 0xC3, 0x16,
           0xEF, 0x3A, 0x90, 0x45, 0x11, 0xC4, 0x6E, 0xBB, 0xC6, 0x13, 0xB9, 0x6C, 0x38, 0xED, 0x47, 0x92,
           0xBD, 0x68, 0xC2, 0x17, 0x43, 0x96, 0x3C, 0xE9, 0x94, 0x41, 0xEB, 0x3E, 0x6A, 0xBF, 0x15, 0xC0,
           0x4B, 0x9E, 0x34, 0xE1, 0xB5, 0x60, 0xCA, 0x1F, 0x62, 0xB7, 0x1D, 0xC8, 0x9C, 0x49, 0xE3, 0x36,
           0x19, 0xCC, 0x66, 0xB3, 0xE7, 0x32, 0x98, 0x4D, 0x30, 0xE5, 0x4F, 0x9A, 0xCE, 0x1B, 0xB1, 0x64,
           0x72, 0xA7, 0x0D, 0xD8, 0x8C, 0x59, 0xF3, 0x26, 0x5B, 0x8E, 0x24, 0xF1, 0xA5, 0x70, 0xDA, 0x0F,
           0x20, 0xF5, 0x5F, 0x8A, 0xDE, 0x0B, 0xA1, 0x74, 0x09, 0xDC, 0x76, 0xA3, 0xF7, 0x22, 0x88, 0x5D,
           0xD6, 0x03, 0xA9, 0x7C, 0x28, 0xFD, 0x57, 0x82, 0xFF, 0x2A, 0x80, 0x55, 0x01, 0xD4, 0x7E, 0xAB,
           0x84, 0x51, 0xFB, 0x2E, 0x7A, 0xAF, 0x05, 0xD0, 0xAD, 0x78, 0xD2, 0x07, 0x53, 0x86, 0x2C, 0xF9]

    def __init__(self, initial_string=b'', initial_start=0x00):
        """Create a new crc8 hash instance."""
        self._sum = initial_start
        self._update(initial_string)

    def update(self, bytes_):
        """Update the hash object with the string arg.
        Repeated calls are equivalent to a single call with the concatenation
        of all the arguments: m.update(a); m.update(b) is equivalent
        to m.update(a+b).
        """
        self._update(bytes_)

    def digest(self):
        """Return the digest of the bytes passed to the update() method so far.
        This is a string of digest_size bytes which may contain non-ASCII
        characters, including null bytes.
        """
        return self._digest()

    def hexdigest(self):
        """Return digest() as hexadecimal string.
        Like digest() except the digest is returned as a string of double
        length, containing only hexadecimal digits. This may be used to
        exchange the value safely in email or other non-binary environments.
        """
        return hex(self._sum)[2:].zfill(2)

    if PY2:
        def _update(self, bytes_):
            if isinstance(bytes_, unicode):
                bytes_ = bytes_.encode()
            elif not isinstance(bytes_, str):
                raise TypeError("must be string or buffer")
            table = self._table
            _sum = self._sum
            for byte in bytes_:
                _sum = table[_sum ^ ord(byte)]
            self._sum = _sum

        def _digest(self):
            return chr(self._sum)
    else:
        def _update(self, bytes_):
            if isinstance(bytes_, str):
                raise TypeError("Unicode-objects must be encoded before"\
                                " hashing")
            elif not isinstance(bytes_, (bytes, bytearray)):
                raise TypeError("object supporting the buffer API required")
            table = self._table
            _sum = self._sum
            for byte in bytes_:
                _sum = table[_sum ^ byte]
            self._sum = _sum

        def _digest(self):
            return bytes([self._sum])

    def copy(self):
        """Return a copy ("clone") of the hash object.

        This can be used to efficiently compute the digests of strings that
        share a common initial substring.
        """
        crc = crc8()
        crc._sum = self._sum
        return crc


__all__ = ['crc8']