mirror of https://github.com/bochs-emu/Bochs
67 lines
2.3 KiB
C++
67 lines
2.3 KiB
C++
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// I grabbed these CRC routines from the following source:
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// http://www.landfield.com/faqs/compression-faq/part1/section-25.html
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//
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// These routines are very useful, so I'm including them in bochs.
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// They are not covered by the license, as they are not my doing.
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// My gratitude to the author for offering them on the 'net.
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//
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// I only changed the u_long to unsigned long, and u_char to unsigned char,
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// and gave the functions prototypes.
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//
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// -Kevin
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//
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// **************************************************************************
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// The following C code (by Rob Warnock <rpw3@sgi.com>) does CRC-32 in
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// BigEndian/BigEndian byte/bit order. That is, the data is sent most
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// significant byte first, and each of the bits within a byte is sent most
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// significant bit first, as in FDDI. You will need to twiddle with it to do
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// Ethernet CRC, i.e., BigEndian/LittleEndian byte/bit order. [Left as an
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// exercise for the reader.]
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//
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// The CRCs this code generates agree with the vendor-supplied Verilog models
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// of several of the popular FDDI "MAC" chips.
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// **************************************************************************
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#include "bochs.h"
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unsigned long crc32_table[256];
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/* Initialized first time "crc32()" is called. If you prefer, you can
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* statically initialize it at compile time. [Another exercise.]
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*/
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unsigned long crc32(unsigned char *buf, int len);
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static void init_crc32(void);
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unsigned long crc32(unsigned char *buf, int len)
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{
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unsigned char *p;
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unsigned long crc;
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if (!crc32_table[1]) /* if not already done, */
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init_crc32(); /* build table */
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crc = 0xffffffff; /* preload shift register, per CRC-32 spec */
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for (p = buf; len > 0; ++p, --len)
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crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
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return ~crc; /* transmit complement, per CRC-32 spec */
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}
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/*
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* Build auxiliary table for parallel byte-at-a-time CRC-32.
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*/
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#define CRC32_POLY 0x04c11db7 /* AUTODIN II, Ethernet, & FDDI */
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void
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init_crc32(void)
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{
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int i, j;
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unsigned long c;
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for (i = 0; i < 256; ++i) {
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for (c = i << 24, j = 8; j > 0; --j)
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c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1);
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crc32_table[i] = c;
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}
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}
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