Python equivalente a la función cksum de unix

checksum zlib

Question

He estado buscando el método de python equivalente para el comando cksum de unix:

http://pubs.opengroup.org/onlinepubs/7990989775/xcu/cksum.html

$ cksum ./temp.bin
1605138151 712368 ./temp.bin

Hasta ahora he encontrado la función zlib.crc32 ()

>>> import zlib
>>> f = open(''./temp.bin'',''rb'')
>>> data = f.read()
>>> zlib.crc32(data)
1128751837

Sin embargo, este código parece producir resultados diferentes. Por lo que puedo decir, esto debería estar usando el mismo polinomio crc, pero imagino que debe haber alguna diferencia en el orden de bytes o los valores iniciales. ¿Alguien puede arrojar algo de luz sobre esto para mí?

Answer 1

Encontré un fragmento here que implementa un cksum compatible en python:

"""
This module implements the cksum command found in most UNIXes in pure
python.

The constants and routine are cribbed from the POSIX man page
"""
import sys

crctab = [ 0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc,
        0x17c56b6b, 0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f,
        0x2f8ad6d6, 0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a,
        0x384fbdbd, 0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
        0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75, 0x6a1936c8,
        0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
        0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e,
        0x95609039, 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
        0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84,
        0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d, 0xd4326d90, 0xd0f37027,
        0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022,
        0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
        0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077,
        0x30476dc0, 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c,
        0x2e003dc5, 0x2ac12072, 0x128e9dcf, 0x164f8078, 0x1b0ca6a1,
        0x1fcdbb16, 0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
        0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb,
        0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
        0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d,
        0x40d816ba, 0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
        0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692, 0x8aad2b2f,
        0x8e6c3698, 0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044,
        0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050, 0xe9362689,
        0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
        0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683,
        0xd1799b34, 0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59,
        0x608edb80, 0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c,
        0x774bb0eb, 0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
        0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53, 0x251d3b9e,
        0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
        0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48,
        0x0e56f0ff, 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
        0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2,
        0xe6ea3d65, 0xeba91bbc, 0xef68060b, 0xd727bbb6, 0xd3e6a601,
        0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604,
        0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
        0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6,
        0x9ff77d71, 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad,
        0x81b02d74, 0x857130c3, 0x5d8a9099, 0x594b8d2e, 0x5408abf7,
        0x50c9b640, 0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
        0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd,
        0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
        0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b,
        0x0fdc1bec, 0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
        0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654, 0xc5a92679,
        0xc1683bce, 0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12,
        0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676, 0xea23f0af,
        0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
        0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5,
        0x9e7d9662, 0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06,
        0xa6322bdf, 0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03,
        0xb1f740b4 ]

UNSIGNED = lambda n: n & 0xffffffff

def memcrc(b):
    n = len(b)
    i = c = s = 0
    for ch in b:
        c = ord(ch)
        tabidx = (s>>24)^c
        s = UNSIGNED((s << 8)) ^ crctab[tabidx]

    while n:
        c = n & 0377
        n = n >> 8
        s = UNSIGNED(s << 8) ^ crctab[(s >> 24) ^ c]
    return UNSIGNED(~s)

if __name__ == ''__main__'':
    fname = sys.argv[-1]
    buffer = open(fname, ''rb'').read()
    print "%d/t%d/t%s" %  (memcrc(buffer), len(buffer), fname)

Probado brevemente, parece funcionar bien.

Answer 2

Lo mismo para python3

import sys

crctab = [ 0x00000000, 0x04c11db7, 0x09823b6e, 0x0d4326d9, 0x130476dc,
        0x17c56b6b, 0x1a864db2, 0x1e475005, 0x2608edb8, 0x22c9f00f,
        0x2f8ad6d6, 0x2b4bcb61, 0x350c9b64, 0x31cd86d3, 0x3c8ea00a,
        0x384fbdbd, 0x4c11db70, 0x48d0c6c7, 0x4593e01e, 0x4152fda9,
        0x5f15adac, 0x5bd4b01b, 0x569796c2, 0x52568b75, 0x6a1936c8,
        0x6ed82b7f, 0x639b0da6, 0x675a1011, 0x791d4014, 0x7ddc5da3,
        0x709f7b7a, 0x745e66cd, 0x9823b6e0, 0x9ce2ab57, 0x91a18d8e,
        0x95609039, 0x8b27c03c, 0x8fe6dd8b, 0x82a5fb52, 0x8664e6e5,
        0xbe2b5b58, 0xbaea46ef, 0xb7a96036, 0xb3687d81, 0xad2f2d84,
        0xa9ee3033, 0xa4ad16ea, 0xa06c0b5d, 0xd4326d90, 0xd0f37027,
        0xddb056fe, 0xd9714b49, 0xc7361b4c, 0xc3f706fb, 0xceb42022,
        0xca753d95, 0xf23a8028, 0xf6fb9d9f, 0xfbb8bb46, 0xff79a6f1,
        0xe13ef6f4, 0xe5ffeb43, 0xe8bccd9a, 0xec7dd02d, 0x34867077,
        0x30476dc0, 0x3d044b19, 0x39c556ae, 0x278206ab, 0x23431b1c,
        0x2e003dc5, 0x2ac12072, 0x128e9dcf, 0x164f8078, 0x1b0ca6a1,
        0x1fcdbb16, 0x018aeb13, 0x054bf6a4, 0x0808d07d, 0x0cc9cdca,
        0x7897ab07, 0x7c56b6b0, 0x71159069, 0x75d48dde, 0x6b93dddb,
        0x6f52c06c, 0x6211e6b5, 0x66d0fb02, 0x5e9f46bf, 0x5a5e5b08,
        0x571d7dd1, 0x53dc6066, 0x4d9b3063, 0x495a2dd4, 0x44190b0d,
        0x40d816ba, 0xaca5c697, 0xa864db20, 0xa527fdf9, 0xa1e6e04e,
        0xbfa1b04b, 0xbb60adfc, 0xb6238b25, 0xb2e29692, 0x8aad2b2f,
        0x8e6c3698, 0x832f1041, 0x87ee0df6, 0x99a95df3, 0x9d684044,
        0x902b669d, 0x94ea7b2a, 0xe0b41de7, 0xe4750050, 0xe9362689,
        0xedf73b3e, 0xf3b06b3b, 0xf771768c, 0xfa325055, 0xfef34de2,
        0xc6bcf05f, 0xc27dede8, 0xcf3ecb31, 0xcbffd686, 0xd5b88683,
        0xd1799b34, 0xdc3abded, 0xd8fba05a, 0x690ce0ee, 0x6dcdfd59,
        0x608edb80, 0x644fc637, 0x7a089632, 0x7ec98b85, 0x738aad5c,
        0x774bb0eb, 0x4f040d56, 0x4bc510e1, 0x46863638, 0x42472b8f,
        0x5c007b8a, 0x58c1663d, 0x558240e4, 0x51435d53, 0x251d3b9e,
        0x21dc2629, 0x2c9f00f0, 0x285e1d47, 0x36194d42, 0x32d850f5,
        0x3f9b762c, 0x3b5a6b9b, 0x0315d626, 0x07d4cb91, 0x0a97ed48,
        0x0e56f0ff, 0x1011a0fa, 0x14d0bd4d, 0x19939b94, 0x1d528623,
        0xf12f560e, 0xf5ee4bb9, 0xf8ad6d60, 0xfc6c70d7, 0xe22b20d2,
        0xe6ea3d65, 0xeba91bbc, 0xef68060b, 0xd727bbb6, 0xd3e6a601,
        0xdea580d8, 0xda649d6f, 0xc423cd6a, 0xc0e2d0dd, 0xcda1f604,
        0xc960ebb3, 0xbd3e8d7e, 0xb9ff90c9, 0xb4bcb610, 0xb07daba7,
        0xae3afba2, 0xaafbe615, 0xa7b8c0cc, 0xa379dd7b, 0x9b3660c6,
        0x9ff77d71, 0x92b45ba8, 0x9675461f, 0x8832161a, 0x8cf30bad,
        0x81b02d74, 0x857130c3, 0x5d8a9099, 0x594b8d2e, 0x5408abf7,
        0x50c9b640, 0x4e8ee645, 0x4a4ffbf2, 0x470cdd2b, 0x43cdc09c,
        0x7b827d21, 0x7f436096, 0x7200464f, 0x76c15bf8, 0x68860bfd,
        0x6c47164a, 0x61043093, 0x65c52d24, 0x119b4be9, 0x155a565e,
        0x18197087, 0x1cd86d30, 0x029f3d35, 0x065e2082, 0x0b1d065b,
        0x0fdc1bec, 0x3793a651, 0x3352bbe6, 0x3e119d3f, 0x3ad08088,
        0x2497d08d, 0x2056cd3a, 0x2d15ebe3, 0x29d4f654, 0xc5a92679,
        0xc1683bce, 0xcc2b1d17, 0xc8ea00a0, 0xd6ad50a5, 0xd26c4d12,
        0xdf2f6bcb, 0xdbee767c, 0xe3a1cbc1, 0xe760d676, 0xea23f0af,
        0xeee2ed18, 0xf0a5bd1d, 0xf464a0aa, 0xf9278673, 0xfde69bc4,
        0x89b8fd09, 0x8d79e0be, 0x803ac667, 0x84fbdbd0, 0x9abc8bd5,
        0x9e7d9662, 0x933eb0bb, 0x97ffad0c, 0xafb010b1, 0xab710d06,
        0xa6322bdf, 0xa2f33668, 0xbcb4666d, 0xb8757bda, 0xb5365d03,
        0xb1f740b4 ]

UNSIGNED = lambda n: n & 0xffffffff

def memcrc(b):
    n = len(b)
    i = c = s = 0
    for c in b:
        tabidx = (s>>24)^c
        s = UNSIGNED((s << 8)) ^ crctab[tabidx]
    while n:
        c = n & 0o0377
        n = n >> 8
        s = UNSIGNED(s << 8) ^ crctab[(s >> 24) ^ c]
    return UNSIGNED(~s)

if __name__ == ''__main__'':
    fname = sys.argv[-1]
    buffer = open(fname, ''rb'').read()
    print("%d/t%d/t%s" %  (memcrc(buffer), len(buffer), fname))