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      1 #!/usr/bin/env python
      2 #
      3 # Copyright 2009 Google Inc. All Rights Reserved.
      4 
      5 """Implementation of CRC-32C checksumming as in rfc3720 section B.4.
      6 
      7 See http://en.wikipedia.org/wiki/Cyclic_redundancy_check for details on CRC-32C.
      8 
      9 This code is a manual python translation of c code generated by
     10 pycrc 0.7.1 (http://www.tty1.net/pycrc/). Command line used:
     11 './pycrc.py --model=crc-32c --generate c --algorithm=table-driven'
     12 """
     13 
     14 
     15 
     16 # TODO(user): We would really benefit from having this as a c extension.
     17 
     18 import array
     19 
     20 CRC_TABLE = (
     21     0x00000000L, 0xf26b8303L, 0xe13b70f7L, 0x1350f3f4L,
     22     0xc79a971fL, 0x35f1141cL, 0x26a1e7e8L, 0xd4ca64ebL,
     23     0x8ad958cfL, 0x78b2dbccL, 0x6be22838L, 0x9989ab3bL,
     24     0x4d43cfd0L, 0xbf284cd3L, 0xac78bf27L, 0x5e133c24L,
     25     0x105ec76fL, 0xe235446cL, 0xf165b798L, 0x030e349bL,
     26     0xd7c45070L, 0x25afd373L, 0x36ff2087L, 0xc494a384L,
     27     0x9a879fa0L, 0x68ec1ca3L, 0x7bbcef57L, 0x89d76c54L,
     28     0x5d1d08bfL, 0xaf768bbcL, 0xbc267848L, 0x4e4dfb4bL,
     29     0x20bd8edeL, 0xd2d60dddL, 0xc186fe29L, 0x33ed7d2aL,
     30     0xe72719c1L, 0x154c9ac2L, 0x061c6936L, 0xf477ea35L,
     31     0xaa64d611L, 0x580f5512L, 0x4b5fa6e6L, 0xb93425e5L,
     32     0x6dfe410eL, 0x9f95c20dL, 0x8cc531f9L, 0x7eaeb2faL,
     33     0x30e349b1L, 0xc288cab2L, 0xd1d83946L, 0x23b3ba45L,
     34     0xf779deaeL, 0x05125dadL, 0x1642ae59L, 0xe4292d5aL,
     35     0xba3a117eL, 0x4851927dL, 0x5b016189L, 0xa96ae28aL,
     36     0x7da08661L, 0x8fcb0562L, 0x9c9bf696L, 0x6ef07595L,
     37     0x417b1dbcL, 0xb3109ebfL, 0xa0406d4bL, 0x522bee48L,
     38     0x86e18aa3L, 0x748a09a0L, 0x67dafa54L, 0x95b17957L,
     39     0xcba24573L, 0x39c9c670L, 0x2a993584L, 0xd8f2b687L,
     40     0x0c38d26cL, 0xfe53516fL, 0xed03a29bL, 0x1f682198L,
     41     0x5125dad3L, 0xa34e59d0L, 0xb01eaa24L, 0x42752927L,
     42     0x96bf4dccL, 0x64d4cecfL, 0x77843d3bL, 0x85efbe38L,
     43     0xdbfc821cL, 0x2997011fL, 0x3ac7f2ebL, 0xc8ac71e8L,
     44     0x1c661503L, 0xee0d9600L, 0xfd5d65f4L, 0x0f36e6f7L,
     45     0x61c69362L, 0x93ad1061L, 0x80fde395L, 0x72966096L,
     46     0xa65c047dL, 0x5437877eL, 0x4767748aL, 0xb50cf789L,
     47     0xeb1fcbadL, 0x197448aeL, 0x0a24bb5aL, 0xf84f3859L,
     48     0x2c855cb2L, 0xdeeedfb1L, 0xcdbe2c45L, 0x3fd5af46L,
     49     0x7198540dL, 0x83f3d70eL, 0x90a324faL, 0x62c8a7f9L,
     50     0xb602c312L, 0x44694011L, 0x5739b3e5L, 0xa55230e6L,
     51     0xfb410cc2L, 0x092a8fc1L, 0x1a7a7c35L, 0xe811ff36L,
     52     0x3cdb9bddL, 0xceb018deL, 0xdde0eb2aL, 0x2f8b6829L,
     53     0x82f63b78L, 0x709db87bL, 0x63cd4b8fL, 0x91a6c88cL,
     54     0x456cac67L, 0xb7072f64L, 0xa457dc90L, 0x563c5f93L,
     55     0x082f63b7L, 0xfa44e0b4L, 0xe9141340L, 0x1b7f9043L,
     56     0xcfb5f4a8L, 0x3dde77abL, 0x2e8e845fL, 0xdce5075cL,
     57     0x92a8fc17L, 0x60c37f14L, 0x73938ce0L, 0x81f80fe3L,
     58     0x55326b08L, 0xa759e80bL, 0xb4091bffL, 0x466298fcL,
     59     0x1871a4d8L, 0xea1a27dbL, 0xf94ad42fL, 0x0b21572cL,
     60     0xdfeb33c7L, 0x2d80b0c4L, 0x3ed04330L, 0xccbbc033L,
     61     0xa24bb5a6L, 0x502036a5L, 0x4370c551L, 0xb11b4652L,
     62     0x65d122b9L, 0x97baa1baL, 0x84ea524eL, 0x7681d14dL,
     63     0x2892ed69L, 0xdaf96e6aL, 0xc9a99d9eL, 0x3bc21e9dL,
     64     0xef087a76L, 0x1d63f975L, 0x0e330a81L, 0xfc588982L,
     65     0xb21572c9L, 0x407ef1caL, 0x532e023eL, 0xa145813dL,
     66     0x758fe5d6L, 0x87e466d5L, 0x94b49521L, 0x66df1622L,
     67     0x38cc2a06L, 0xcaa7a905L, 0xd9f75af1L, 0x2b9cd9f2L,
     68     0xff56bd19L, 0x0d3d3e1aL, 0x1e6dcdeeL, 0xec064eedL,
     69     0xc38d26c4L, 0x31e6a5c7L, 0x22b65633L, 0xd0ddd530L,
     70     0x0417b1dbL, 0xf67c32d8L, 0xe52cc12cL, 0x1747422fL,
     71     0x49547e0bL, 0xbb3ffd08L, 0xa86f0efcL, 0x5a048dffL,
     72     0x8ecee914L, 0x7ca56a17L, 0x6ff599e3L, 0x9d9e1ae0L,
     73     0xd3d3e1abL, 0x21b862a8L, 0x32e8915cL, 0xc083125fL,
     74     0x144976b4L, 0xe622f5b7L, 0xf5720643L, 0x07198540L,
     75     0x590ab964L, 0xab613a67L, 0xb831c993L, 0x4a5a4a90L,
     76     0x9e902e7bL, 0x6cfbad78L, 0x7fab5e8cL, 0x8dc0dd8fL,
     77     0xe330a81aL, 0x115b2b19L, 0x020bd8edL, 0xf0605beeL,
     78     0x24aa3f05L, 0xd6c1bc06L, 0xc5914ff2L, 0x37faccf1L,
     79     0x69e9f0d5L, 0x9b8273d6L, 0x88d28022L, 0x7ab90321L,
     80     0xae7367caL, 0x5c18e4c9L, 0x4f48173dL, 0xbd23943eL,
     81     0xf36e6f75L, 0x0105ec76L, 0x12551f82L, 0xe03e9c81L,
     82     0x34f4f86aL, 0xc69f7b69L, 0xd5cf889dL, 0x27a40b9eL,
     83     0x79b737baL, 0x8bdcb4b9L, 0x988c474dL, 0x6ae7c44eL,
     84     0xbe2da0a5L, 0x4c4623a6L, 0x5f16d052L, 0xad7d5351L,
     85     )
     86 
     87 
     88 # initial CRC value
     89 CRC_INIT = 0
     90 
     91 _MASK = 0xFFFFFFFFL
     92 
     93 
     94 def crc_update(crc, data):
     95   """Update CRC-32C checksum with data.
     96 
     97   Args:
     98     crc: 32-bit checksum to update as long.
     99     data: byte array, string or iterable over bytes.
    100 
    101   Returns:
    102     32-bit updated CRC-32C as long.
    103   """
    104   # Convert data to byte array if needed
    105   if type(data) != array.array or data.itemsize != 1:
    106     buf = array.array("B", data)
    107   else:
    108     buf = data
    109 
    110   crc = crc ^ _MASK
    111   for b in buf:
    112     table_index = (crc ^ b) & 0xff
    113     crc = (CRC_TABLE[table_index] ^ (crc >> 8)) & _MASK
    114   return crc ^ _MASK
    115 
    116 
    117 def crc_finalize(crc):
    118   """Finalize CRC-32C checksum.
    119 
    120   This function should be called as last step of crc calculation.
    121 
    122   Args:
    123     crc: 32-bit checksum as long.
    124 
    125   Returns:
    126     finalized 32-bit checksum as long
    127   """
    128   return crc & _MASK
    129 
    130 
    131 def crc(data):
    132   """Compute CRC-32C checksum of the data.
    133 
    134   Args:
    135     data: byte array, string or iterable over bytes.
    136 
    137   Returns:
    138     32-bit CRC-32C checksum of data as long.
    139   """
    140   return crc_finalize(crc_update(CRC_INIT, data))
    141