mirror of https://github.com/python/cpython
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
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44cf8ef521
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7d47c9e38a
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@ -772,6 +772,146 @@ PyObject *args;
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return Py_BuildValue("i", crc);
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}
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static char doc_crc32[] =
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"(data, oldcrc = 0) -> newcrc. Compute CRC-32 incrementally";
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/* Crc - 32 BIT ANSI X3.66 CRC checksum files
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Also known as: ISO 3307
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**********************************************************************|
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* *|
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* Demonstration program to compute the 32-bit CRC used as the frame *|
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* check sequence in ADCCP (ANSI X3.66, also known as FIPS PUB 71 *|
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* and FED-STD-1003, the U.S. versions of CCITT's X.25 link-level *|
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* protocol). The 32-bit FCS was added via the Federal Register, *|
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* 1 June 1982, p.23798. I presume but don't know for certain that *|
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* this polynomial is or will be included in CCITT V.41, which *|
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* defines the 16-bit CRC (often called CRC-CCITT) polynomial. FIPS *|
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* PUB 78 says that the 32-bit FCS reduces otherwise undetected *|
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* errors by a factor of 10^-5 over 16-bit FCS. *|
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* *|
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**********************************************************************|
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Copyright (C) 1986 Gary S. Brown. You may use this program, or
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code or tables extracted from it, as desired without restriction.
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First, the polynomial itself and its table of feedback terms. The
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polynomial is
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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
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Note that we take it "backwards" and put the highest-order term in
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the lowest-order bit. The X^32 term is "implied"; the LSB is the
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X^31 term, etc. The X^0 term (usually shown as "+1") results in
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the MSB being 1.
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Note that the usual hardware shift register implementation, which
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is what we're using (we're merely optimizing it by doing eight-bit
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chunks at a time) shifts bits into the lowest-order term. In our
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implementation, that means shifting towards the right. Why do we
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do it this way? Because the calculated CRC must be transmitted in
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order from highest-order term to lowest-order term. UARTs transmit
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characters in order from LSB to MSB. By storing the CRC this way,
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we hand it to the UART in the order low-byte to high-byte; the UART
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sends each low-bit to hight-bit; and the result is transmission bit
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by bit from highest- to lowest-order term without requiring any bit
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shuffling on our part. Reception works similarly.
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The feedback terms table consists of 256, 32-bit entries. Notes:
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1. The table can be generated at runtime if desired; code to do so
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is shown later. It might not be obvious, but the feedback
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terms simply represent the results of eight shift/xor opera-
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tions for all combinations of data and CRC register values.
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2. The CRC accumulation logic is the same for all CRC polynomials,
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be they sixteen or thirty-two bits wide. You simply choose the
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appropriate table. Alternatively, because the table can be
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generated at runtime, you can start by generating the table for
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the polynomial in question and use exactly the same "updcrc",
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if your application needn't simultaneously handle two CRC
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polynomials. (Note, however, that XMODEM is strange.)
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3. For 16-bit CRCs, the table entries need be only 16 bits wide;
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of course, 32-bit entries work OK if the high 16 bits are zero.
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4. The values must be right-shifted by eight bits by the "updcrc"
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logic; the shift must be unsigned (bring in zeroes). On some
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hardware you could probably optimize the shift in assembler by
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using byte-swap instructions.
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********************************************************************/
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static unsigned long crc_32_tab[256] = {
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0x00000000UL, 0x77073096UL, 0xee0e612cUL, 0x990951baUL, 0x076dc419UL,
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0x706af48fUL, 0xe963a535UL, 0x9e6495a3UL, 0x0edb8832UL, 0x79dcb8a4UL,
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0xe0d5e91eUL, 0x97d2d988UL, 0x09b64c2bUL, 0x7eb17cbdUL, 0xe7b82d07UL,
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0x90bf1d91UL, 0x1db71064UL, 0x6ab020f2UL, 0xf3b97148UL, 0x84be41deUL,
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0x1adad47dUL, 0x6ddde4ebUL, 0xf4d4b551UL, 0x83d385c7UL, 0x136c9856UL,
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0x646ba8c0UL, 0xfd62f97aUL, 0x8a65c9ecUL, 0x14015c4fUL, 0x63066cd9UL,
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0xfa0f3d63UL, 0x8d080df5UL, 0x3b6e20c8UL, 0x4c69105eUL, 0xd56041e4UL,
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0xa2677172UL, 0x3c03e4d1UL, 0x4b04d447UL, 0xd20d85fdUL, 0xa50ab56bUL,
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0x35b5a8faUL, 0x42b2986cUL, 0xdbbbc9d6UL, 0xacbcf940UL, 0x32d86ce3UL,
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0x45df5c75UL, 0xdcd60dcfUL, 0xabd13d59UL, 0x26d930acUL, 0x51de003aUL,
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0xc8d75180UL, 0xbfd06116UL, 0x21b4f4b5UL, 0x56b3c423UL, 0xcfba9599UL,
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0xb8bda50fUL, 0x2802b89eUL, 0x5f058808UL, 0xc60cd9b2UL, 0xb10be924UL,
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0x2f6f7c87UL, 0x58684c11UL, 0xc1611dabUL, 0xb6662d3dUL, 0x76dc4190UL,
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0x01db7106UL, 0x98d220bcUL, 0xefd5102aUL, 0x71b18589UL, 0x06b6b51fUL,
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0x9fbfe4a5UL, 0xe8b8d433UL, 0x7807c9a2UL, 0x0f00f934UL, 0x9609a88eUL,
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0xe10e9818UL, 0x7f6a0dbbUL, 0x086d3d2dUL, 0x91646c97UL, 0xe6635c01UL,
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0x6b6b51f4UL, 0x1c6c6162UL, 0x856530d8UL, 0xf262004eUL, 0x6c0695edUL,
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0x1b01a57bUL, 0x8208f4c1UL, 0xf50fc457UL, 0x65b0d9c6UL, 0x12b7e950UL,
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0x8bbeb8eaUL, 0xfcb9887cUL, 0x62dd1ddfUL, 0x15da2d49UL, 0x8cd37cf3UL,
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0xfbd44c65UL, 0x4db26158UL, 0x3ab551ceUL, 0xa3bc0074UL, 0xd4bb30e2UL,
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0x4adfa541UL, 0x3dd895d7UL, 0xa4d1c46dUL, 0xd3d6f4fbUL, 0x4369e96aUL,
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0x346ed9fcUL, 0xad678846UL, 0xda60b8d0UL, 0x44042d73UL, 0x33031de5UL,
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0xaa0a4c5fUL, 0xdd0d7cc9UL, 0x5005713cUL, 0x270241aaUL, 0xbe0b1010UL,
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0xc90c2086UL, 0x5768b525UL, 0x206f85b3UL, 0xb966d409UL, 0xce61e49fUL,
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0x5edef90eUL, 0x29d9c998UL, 0xb0d09822UL, 0xc7d7a8b4UL, 0x59b33d17UL,
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0x2eb40d81UL, 0xb7bd5c3bUL, 0xc0ba6cadUL, 0xedb88320UL, 0x9abfb3b6UL,
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0x03b6e20cUL, 0x74b1d29aUL, 0xead54739UL, 0x9dd277afUL, 0x04db2615UL,
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0x73dc1683UL, 0xe3630b12UL, 0x94643b84UL, 0x0d6d6a3eUL, 0x7a6a5aa8UL,
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0xe40ecf0bUL, 0x9309ff9dUL, 0x0a00ae27UL, 0x7d079eb1UL, 0xf00f9344UL,
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0x8708a3d2UL, 0x1e01f268UL, 0x6906c2feUL, 0xf762575dUL, 0x806567cbUL,
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0x196c3671UL, 0x6e6b06e7UL, 0xfed41b76UL, 0x89d32be0UL, 0x10da7a5aUL,
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0x67dd4accUL, 0xf9b9df6fUL, 0x8ebeeff9UL, 0x17b7be43UL, 0x60b08ed5UL,
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0xd6d6a3e8UL, 0xa1d1937eUL, 0x38d8c2c4UL, 0x4fdff252UL, 0xd1bb67f1UL,
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0xa6bc5767UL, 0x3fb506ddUL, 0x48b2364bUL, 0xd80d2bdaUL, 0xaf0a1b4cUL,
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0x36034af6UL, 0x41047a60UL, 0xdf60efc3UL, 0xa867df55UL, 0x316e8eefUL,
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0x4669be79UL, 0xcb61b38cUL, 0xbc66831aUL, 0x256fd2a0UL, 0x5268e236UL,
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0xcc0c7795UL, 0xbb0b4703UL, 0x220216b9UL, 0x5505262fUL, 0xc5ba3bbeUL,
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0xb2bd0b28UL, 0x2bb45a92UL, 0x5cb36a04UL, 0xc2d7ffa7UL, 0xb5d0cf31UL,
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0x2cd99e8bUL, 0x5bdeae1dUL, 0x9b64c2b0UL, 0xec63f226UL, 0x756aa39cUL,
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0x026d930aUL, 0x9c0906a9UL, 0xeb0e363fUL, 0x72076785UL, 0x05005713UL,
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0x95bf4a82UL, 0xe2b87a14UL, 0x7bb12baeUL, 0x0cb61b38UL, 0x92d28e9bUL,
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0xe5d5be0dUL, 0x7cdcefb7UL, 0x0bdbdf21UL, 0x86d3d2d4UL, 0xf1d4e242UL,
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0x68ddb3f8UL, 0x1fda836eUL, 0x81be16cdUL, 0xf6b9265bUL, 0x6fb077e1UL,
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0x18b74777UL, 0x88085ae6UL, 0xff0f6a70UL, 0x66063bcaUL, 0x11010b5cUL,
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0x8f659effUL, 0xf862ae69UL, 0x616bffd3UL, 0x166ccf45UL, 0xa00ae278UL,
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0xd70dd2eeUL, 0x4e048354UL, 0x3903b3c2UL, 0xa7672661UL, 0xd06016f7UL,
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0x4969474dUL, 0x3e6e77dbUL, 0xaed16a4aUL, 0xd9d65adcUL, 0x40df0b66UL,
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0x37d83bf0UL, 0xa9bcae53UL, 0xdebb9ec5UL, 0x47b2cf7fUL, 0x30b5ffe9UL,
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0xbdbdf21cUL, 0xcabac28aUL, 0x53b39330UL, 0x24b4a3a6UL, 0xbad03605UL,
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0xcdd70693UL, 0x54de5729UL, 0x23d967bfUL, 0xb3667a2eUL, 0xc4614ab8UL,
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0x5d681b02UL, 0x2a6f2b94UL, 0xb40bbe37UL, 0xc30c8ea1UL, 0x5a05df1bUL,
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0x2d02ef8dUL
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};
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static PyObject *
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binascii_crc32(self, args)
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PyObject *self;
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PyObject *args;
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{ /* By Jim Ahlstrom; All rights transferred to CNRI */
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unsigned char *bin_data;
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unsigned long crc = 0UL; /* initial value of CRC */
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int len;
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if ( !PyArg_ParseTuple(args, "s#|l", &bin_data, &len, &crc) )
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return NULL;
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crc = crc ^ 0xFFFFFFFFUL;
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while(len--)
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crc = crc_32_tab[(crc ^ *bin_data++) & 0xffUL] ^ (crc >> 8);
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/* Note: (crc >> 8) MUST zero fill on left */
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return Py_BuildValue("l", crc ^ 0xFFFFFFFFUL);
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}
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/* List of functions defined in the module */
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static struct PyMethodDef binascii_module_methods[] = {
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@ -788,6 +928,7 @@ static struct PyMethodDef binascii_module_methods[] = {
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{"rledecode_hqx", binascii_rledecode_hqx, 1,
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doc_rledecode_hqx},
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{"crc_hqx", binascii_crc_hqx, 1, doc_crc_hqx},
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{"crc32", binascii_crc32, 1, doc_crc32},
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{NULL, NULL} /* sentinel */
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};
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