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cksum in python

a guest Aug 3rd, 2010 889 Never
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  1. """
  2. This module implements the cksum command found in most UNIXes in pure
  3. python.
  4.  
  5. The constants and routine are cribbed from the POSIX man page
  6. """
  7. import sys
  8.  
  9. crctab = [ 0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc,
  10.         0x17c56b6b, 0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f,
  11.         0x2f8ad6d6, 0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a,
  12.         0x384fbdbd, 0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
  13.         0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75, 0x6a1936c8,
  14.         0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
  15.         0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e,
  16.         0x95609039, 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
  17.         0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84,
  18.         0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d, 0xd4326d90, 0xd0f37027,
  19.         0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022,
  20.         0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
  21.         0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077,
  22.         0x30476dc0, 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c,
  23.         0x2e003dc5, 0x2ac12072, 0x128e9dcf, 0x164f8078, 0x1b0ca6a1,
  24.         0x1fcdbb16, 0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
  25.         0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb,
  26.         0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
  27.         0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d,
  28.         0x40d816ba, 0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
  29.         0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692, 0x8aad2b2f,
  30.         0x8e6c3698, 0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044,
  31.         0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050, 0xe9362689,
  32.         0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
  33.         0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683,
  34.         0xd1799b34, 0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59,
  35.         0x608edb80, 0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c,
  36.         0x774bb0eb, 0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
  37.         0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53, 0x251d3b9e,
  38.         0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
  39.         0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48,
  40.         0x0e56f0ff, 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
  41.         0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2,
  42.         0xe6ea3d65, 0xeba91bbc, 0xef68060b, 0xd727bbb6, 0xd3e6a601,
  43.         0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604,
  44.         0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
  45.         0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6,
  46.         0x9ff77d71, 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad,
  47.         0x81b02d74, 0x857130c3, 0x5d8a9099, 0x594b8d2e, 0x5408abf7,
  48.         0x50c9b640, 0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
  49.         0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd,
  50.         0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
  51.         0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b,
  52.         0x0fdc1bec, 0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
  53.         0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654, 0xc5a92679,
  54.         0xc1683bce, 0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12,
  55.         0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676, 0xea23f0af,
  56.         0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
  57.         0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5,
  58.         0x9e7d9662, 0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06,
  59.         0xa6322bdf, 0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03,
  60.         0xb1f740b4 ]
  61.  
  62. UNSIGNED = lambda n: n & 0xffffffff
  63.  
  64. def memcrc(b):
  65.     n = len(b)
  66.     i = c = s = 0
  67.     for ch in b:
  68.         c = ord(ch)
  69.         tabidx = (s>>24)^c
  70.         s = UNSIGNED((s << 8)) ^ crctab[tabidx]
  71.  
  72.     while n:
  73.         c = n & 0377
  74.         n = n >> 8
  75.         s = UNSIGNED(s << 8) ^ crctab[(s >> 24) ^ c]
  76.     return UNSIGNED(~s)
  77.  
  78. if __name__ == '__main__':
  79.     fname = sys.argv[-1]
  80.     buffer = open(fname, 'rb').read()
  81.     print "%d\t%d\t%s" %  (memcrc(buffer), len(buffer), fname)
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