[Patches] Re: Add crc32() method to binascii
James C. Ahlstrom
jim@interet.com
Mon, 14 Feb 2000 15:15:59 -0500
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This is a corrected patch. Thanks to Tim Peters for helpful comments.
This patch adds a new method to module binascii. It calculates
a CRC-32 checksum. This method is generally useful, and is
required for ZIP file checksums.
LEGAL
=====
I confirm that, to the best of my knowledge and belief, this
contribution is free of any claims of third parties under
copyright, patent or other rights or interests ("claims"). To
the extent that I have any such claims, I hereby grant to CNRI a
nonexclusive, irrevocable, royalty-free, worldwide license to
reproduce, distribute, perform and/or display publicly, prepare
derivative versions, and otherwise use this contribution as part
of the Python software and its related documentation, or any
derivative versions thereof, at no cost to CNRI or its licensed
users, and to authorize others to do so.
I acknowledge that CNRI may, at its sole discretion, decide
whether or not to incorporate this contribution in the Python
software and its related documentation. I further grant CNRI
permission to use my name and other identifying information
provided to CNRI by me for use in connection with the Python
software and its related documentation.
DOCS (add to binascii docs)
===========================
crc32(data, crc = 0)
Compute CRC-32, the 32-bit checksum of data, starting with an initial
crc. This is consistent with the ZIP file checksum. Use as follows:
print binascii.crc32("hello world")
# Or, in two pieces:
crc = binascii.crc32("hello")
crc = binascii.crc32(" world", crc)
print crc
TEST (add to ./test/test_binascii.py)
=====================================
*** test_binascii.py.orig Mon Feb 14 09:41:24 2000
--- test_binascii.py Mon Feb 14 09:58:36 2000
***************
*** 5,14 ****
--- 5,19 ----
Roger E. Masse
"""
import binhex
+ import binascii
import tempfile
from test_support import verbose
def test():
+ crc = binascii.crc32("Test the CRC-32 of")
+ crc = binascii.crc32(" this string.", crc)
+ if crc != 1571220330:
+ print "binascii.crc32() failed."
try:
fname1 = tempfile.mktemp()
PATCH against 1.5.2 release (but just an addition)
==================================================
See attached.
JimA
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*** binascii.c.orig Mon Feb 7 15:50:26 2000
--- binascii.c Mon Feb 14 09:37:56 2000
***************
*** 719,724 ****
--- 719,864 ----
return Py_BuildValue("i", crc);
}
+ static char doc_crc32[] =
+ "(data, oldcrc = 0) -> newcrc. Compute CRC-32 incrementally";
+
+ /* Crc - 32 BIT ANSI X3.66 CRC checksum files
+ Also known as: ISO 3307
+ **********************************************************************|
+ * *|
+ * Demonstration program to compute the 32-bit CRC used as the frame *|
+ * check sequence in ADCCP (ANSI X3.66, also known as FIPS PUB 71 *|
+ * and FED-STD-1003, the U.S. versions of CCITT's X.25 link-level *|
+ * protocol). The 32-bit FCS was added via the Federal Register, *|
+ * 1 June 1982, p.23798. I presume but don't know for certain that *|
+ * this polynomial is or will be included in CCITT V.41, which *|
+ * defines the 16-bit CRC (often called CRC-CCITT) polynomial. FIPS *|
+ * PUB 78 says that the 32-bit FCS reduces otherwise undetected *|
+ * errors by a factor of 10^-5 over 16-bit FCS. *|
+ * *|
+ **********************************************************************|
+
+ Copyright (C) 1986 Gary S. Brown. You may use this program, or
+ code or tables extracted from it, as desired without restriction.
+
+ First, the polynomial itself and its table of feedback terms. The
+ polynomial is
+ X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
+ Note that we take it "backwards" and put the highest-order term in
+ the lowest-order bit. The X^32 term is "implied"; the LSB is the
+ X^31 term, etc. The X^0 term (usually shown as "+1") results in
+ the MSB being 1.
+
+ Note that the usual hardware shift register implementation, which
+ is what we're using (we're merely optimizing it by doing eight-bit
+ chunks at a time) shifts bits into the lowest-order term. In our
+ implementation, that means shifting towards the right. Why do we
+ do it this way? Because the calculated CRC must be transmitted in
+ order from highest-order term to lowest-order term. UARTs transmit
+ characters in order from LSB to MSB. By storing the CRC this way,
+ we hand it to the UART in the order low-byte to high-byte; the UART
+ sends each low-bit to hight-bit; and the result is transmission bit
+ by bit from highest- to lowest-order term without requiring any bit
+ shuffling on our part. Reception works similarly.
+
+ The feedback terms table consists of 256, 32-bit entries. Notes:
+
+ 1. The table can be generated at runtime if desired; code to do so
+ is shown later. It might not be obvious, but the feedback
+ terms simply represent the results of eight shift/xor opera-
+ tions for all combinations of data and CRC register values.
+
+ 2. The CRC accumulation logic is the same for all CRC polynomials,
+ be they sixteen or thirty-two bits wide. You simply choose the
+ appropriate table. Alternatively, because the table can be
+ generated at runtime, you can start by generating the table for
+ the polynomial in question and use exactly the same "updcrc",
+ if your application needn't simultaneously handle two CRC
+ polynomials. (Note, however, that XMODEM is strange.)
+
+ 3. For 16-bit CRCs, the table entries need be only 16 bits wide;
+ of course, 32-bit entries work OK if the high 16 bits are zero.
+
+ 4. The values must be right-shifted by eight bits by the "updcrc"
+ logic; the shift must be unsigned (bring in zeroes). On some
+ hardware you could probably optimize the shift in assembler by
+ using byte-swap instructions.
+ ********************************************************************/
+
+ static unsigned long crc_32_tab[256] = {
+ 0x00000000UL, 0x77073096UL, 0xee0e612cUL, 0x990951baUL, 0x076dc419UL,
+ 0x706af48fUL, 0xe963a535UL, 0x9e6495a3UL, 0x0edb8832UL, 0x79dcb8a4UL,
+ 0xe0d5e91eUL, 0x97d2d988UL, 0x09b64c2bUL, 0x7eb17cbdUL, 0xe7b82d07UL,
+ 0x90bf1d91UL, 0x1db71064UL, 0x6ab020f2UL, 0xf3b97148UL, 0x84be41deUL,
+ 0x1adad47dUL, 0x6ddde4ebUL, 0xf4d4b551UL, 0x83d385c7UL, 0x136c9856UL,
+ 0x646ba8c0UL, 0xfd62f97aUL, 0x8a65c9ecUL, 0x14015c4fUL, 0x63066cd9UL,
+ 0xfa0f3d63UL, 0x8d080df5UL, 0x3b6e20c8UL, 0x4c69105eUL, 0xd56041e4UL,
+ 0xa2677172UL, 0x3c03e4d1UL, 0x4b04d447UL, 0xd20d85fdUL, 0xa50ab56bUL,
+ 0x35b5a8faUL, 0x42b2986cUL, 0xdbbbc9d6UL, 0xacbcf940UL, 0x32d86ce3UL,
+ 0x45df5c75UL, 0xdcd60dcfUL, 0xabd13d59UL, 0x26d930acUL, 0x51de003aUL,
+ 0xc8d75180UL, 0xbfd06116UL, 0x21b4f4b5UL, 0x56b3c423UL, 0xcfba9599UL,
+ 0xb8bda50fUL, 0x2802b89eUL, 0x5f058808UL, 0xc60cd9b2UL, 0xb10be924UL,
+ 0x2f6f7c87UL, 0x58684c11UL, 0xc1611dabUL, 0xb6662d3dUL, 0x76dc4190UL,
+ 0x01db7106UL, 0x98d220bcUL, 0xefd5102aUL, 0x71b18589UL, 0x06b6b51fUL,
+ 0x9fbfe4a5UL, 0xe8b8d433UL, 0x7807c9a2UL, 0x0f00f934UL, 0x9609a88eUL,
+ 0xe10e9818UL, 0x7f6a0dbbUL, 0x086d3d2dUL, 0x91646c97UL, 0xe6635c01UL,
+ 0x6b6b51f4UL, 0x1c6c6162UL, 0x856530d8UL, 0xf262004eUL, 0x6c0695edUL,
+ 0x1b01a57bUL, 0x8208f4c1UL, 0xf50fc457UL, 0x65b0d9c6UL, 0x12b7e950UL,
+ 0x8bbeb8eaUL, 0xfcb9887cUL, 0x62dd1ddfUL, 0x15da2d49UL, 0x8cd37cf3UL,
+ 0xfbd44c65UL, 0x4db26158UL, 0x3ab551ceUL, 0xa3bc0074UL, 0xd4bb30e2UL,
+ 0x4adfa541UL, 0x3dd895d7UL, 0xa4d1c46dUL, 0xd3d6f4fbUL, 0x4369e96aUL,
+ 0x346ed9fcUL, 0xad678846UL, 0xda60b8d0UL, 0x44042d73UL, 0x33031de5UL,
+ 0xaa0a4c5fUL, 0xdd0d7cc9UL, 0x5005713cUL, 0x270241aaUL, 0xbe0b1010UL,
+ 0xc90c2086UL, 0x5768b525UL, 0x206f85b3UL, 0xb966d409UL, 0xce61e49fUL,
+ 0x5edef90eUL, 0x29d9c998UL, 0xb0d09822UL, 0xc7d7a8b4UL, 0x59b33d17UL,
+ 0x2eb40d81UL, 0xb7bd5c3bUL, 0xc0ba6cadUL, 0xedb88320UL, 0x9abfb3b6UL,
+ 0x03b6e20cUL, 0x74b1d29aUL, 0xead54739UL, 0x9dd277afUL, 0x04db2615UL,
+ 0x73dc1683UL, 0xe3630b12UL, 0x94643b84UL, 0x0d6d6a3eUL, 0x7a6a5aa8UL,
+ 0xe40ecf0bUL, 0x9309ff9dUL, 0x0a00ae27UL, 0x7d079eb1UL, 0xf00f9344UL,
+ 0x8708a3d2UL, 0x1e01f268UL, 0x6906c2feUL, 0xf762575dUL, 0x806567cbUL,
+ 0x196c3671UL, 0x6e6b06e7UL, 0xfed41b76UL, 0x89d32be0UL, 0x10da7a5aUL,
+ 0x67dd4accUL, 0xf9b9df6fUL, 0x8ebeeff9UL, 0x17b7be43UL, 0x60b08ed5UL,
+ 0xd6d6a3e8UL, 0xa1d1937eUL, 0x38d8c2c4UL, 0x4fdff252UL, 0xd1bb67f1UL,
+ 0xa6bc5767UL, 0x3fb506ddUL, 0x48b2364bUL, 0xd80d2bdaUL, 0xaf0a1b4cUL,
+ 0x36034af6UL, 0x41047a60UL, 0xdf60efc3UL, 0xa867df55UL, 0x316e8eefUL,
+ 0x4669be79UL, 0xcb61b38cUL, 0xbc66831aUL, 0x256fd2a0UL, 0x5268e236UL,
+ 0xcc0c7795UL, 0xbb0b4703UL, 0x220216b9UL, 0x5505262fUL, 0xc5ba3bbeUL,
+ 0xb2bd0b28UL, 0x2bb45a92UL, 0x5cb36a04UL, 0xc2d7ffa7UL, 0xb5d0cf31UL,
+ 0x2cd99e8bUL, 0x5bdeae1dUL, 0x9b64c2b0UL, 0xec63f226UL, 0x756aa39cUL,
+ 0x026d930aUL, 0x9c0906a9UL, 0xeb0e363fUL, 0x72076785UL, 0x05005713UL,
+ 0x95bf4a82UL, 0xe2b87a14UL, 0x7bb12baeUL, 0x0cb61b38UL, 0x92d28e9bUL,
+ 0xe5d5be0dUL, 0x7cdcefb7UL, 0x0bdbdf21UL, 0x86d3d2d4UL, 0xf1d4e242UL,
+ 0x68ddb3f8UL, 0x1fda836eUL, 0x81be16cdUL, 0xf6b9265bUL, 0x6fb077e1UL,
+ 0x18b74777UL, 0x88085ae6UL, 0xff0f6a70UL, 0x66063bcaUL, 0x11010b5cUL,
+ 0x8f659effUL, 0xf862ae69UL, 0x616bffd3UL, 0x166ccf45UL, 0xa00ae278UL,
+ 0xd70dd2eeUL, 0x4e048354UL, 0x3903b3c2UL, 0xa7672661UL, 0xd06016f7UL,
+ 0x4969474dUL, 0x3e6e77dbUL, 0xaed16a4aUL, 0xd9d65adcUL, 0x40df0b66UL,
+ 0x37d83bf0UL, 0xa9bcae53UL, 0xdebb9ec5UL, 0x47b2cf7fUL, 0x30b5ffe9UL,
+ 0xbdbdf21cUL, 0xcabac28aUL, 0x53b39330UL, 0x24b4a3a6UL, 0xbad03605UL,
+ 0xcdd70693UL, 0x54de5729UL, 0x23d967bfUL, 0xb3667a2eUL, 0xc4614ab8UL,
+ 0x5d681b02UL, 0x2a6f2b94UL, 0xb40bbe37UL, 0xc30c8ea1UL, 0x5a05df1bUL,
+ 0x2d02ef8dUL
+ };
+
+ static PyObject *
+ binascii_crc32(self, args)
+ PyObject *self;
+ PyObject *args;
+ { /* By Jim Ahlstrom; All rights transferred to CNRI */
+ unsigned char *bin_data;
+ unsigned long crc = 0UL; /* initial value of CRC */
+ int len;
+
+ if ( !PyArg_ParseTuple(args, "s#|l", &bin_data, &len, &crc) )
+ return NULL;
+
+ crc = crc ^ 0xFFFFFFFFUL;
+ while(len--)
+ crc = crc_32_tab[(crc ^ *bin_data++) & 0xffUL] ^ (crc >> 8);
+ /* Note: (crc >> 8) MUST zero fill on left */
+ return Py_BuildValue("l", crc ^ 0xFFFFFFFFUL);
+ }
+
/* List of functions defined in the module */
static struct PyMethodDef binascii_module_methods[] = {
***************
*** 735,740 ****
--- 875,881 ----
{"rledecode_hqx", binascii_rledecode_hqx, 1,
doc_rledecode_hqx},
{"crc_hqx", binascii_crc_hqx, 1, doc_crc_hqx},
+ {"crc32", binascii_crc32, 1, doc_crc32},
{NULL, NULL} /* sentinel */
};
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