Patch by Jim Ahlstrom to add crc32, a useful checksum function

(e.g. used for ZIP files).

The patch includes code that says:
+  Copyright (C) 1986 Gary S. Brown.  You may use this program, or
+  code or tables extracted from it, as desired without restriction.

My interpretation (and Jim's) is that Gary S Brown has no claims under
copyright, patent or other rights or interests.  Lawyers might disagree.
This commit is contained in:
Guido van Rossum 2000-02-16 21:11:52 +00:00
parent 44cf8ef521
commit 7d47c9e38a
1 changed files with 141 additions and 0 deletions

View File

@ -772,6 +772,146 @@ PyObject *args;
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[] = {
@ -788,6 +928,7 @@ static struct PyMethodDef binascii_module_methods[] = {
{"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 */
};