Version:
~
[ 2.3.5 ] ~
[ 2.3 ] ~
** Warning: Cannot open xref database.
1 /////////////////////////////////////////////////////////////////////////
2 // $Id: crc.cc,v 1.1 2006/01/24 19:03:53 sshwarts Exp $
3 /////////////////////////////////////////////////////////////////////////
4 //
5 // I grabbed these CRC routines from the following source:
6 // http://www.landfield.com/faqs/compression-faq/part1/section-25.html
7 //
8 // These routines are very useful, so I'm including them in bochs.
9 // They are not covered by the license, as they are not my doing.
10 // My gratitude to the author for offering them on the 'net.
11 //
12 // I only changed the u_long to Bit32u, and u_char to Bit8u, and gave
13 // the functions prototypes.
14 //
15 // -Kevin
16 //
17 // **************************************************************************
18 // The following C code (by Rob Warnock <rpw3@sgi.com>) does CRC-32 in
19 // BigEndian/BigEndian byte/bit order. That is, the data is sent most
20 // significant byte first, and each of the bits within a byte is sent most
21 // significant bit first, as in FDDI. You will need to twiddle with it to do
22 // Ethernet CRC, i.e., BigEndian/LittleEndian byte/bit order. [Left as an
23 // exercise for the reader.]
24 //
25 // The CRCs this code generates agree with the vendor-supplied Verilog models
26 // of several of the popular FDDI "MAC" chips.
27 // **************************************************************************
28
29 #include "config.h"
30
31 /* Initialized first time "crc32()" is called. If you prefer, you can
32 * statically initialize it at compile time. [Another exercise.]
33 */
34 static Bit32u crc32_table[256];
35
36 /*
37 * Build auxiliary table for parallel byte-at-a-time CRC-32.
38 */
39 #define CRC32_POLY 0x04c11db7 /* AUTODIN II, Ethernet, & FDDI */
40
41 static void init_crc32(void)
42 {
43 int i, j;
44 Bit32u c;
45
46 for (i = 0; i < 256; ++i) {
47 for (c = i << 24, j = 8; j > 0; --j)
48 c = c & 0x80000000 ? (c << 1) ^ CRC32_POLY : (c << 1);
49 crc32_table[i] = c;
50 }
51 }
52
53 Bit32u crc32(const Bit8u *buf, int len)
54 {
55 const Bit8u *p;
56 Bit32u crc;
57
58 if (!crc32_table[1]) /* if not already done, */
59 init_crc32(); /* build table */
60
61 crc = 0xffffffff; /* preload shift register, per CRC-32 spec */
62 for (p = buf; len > 0; ++p, --len)
63 crc = (crc << 8) ^ crc32_table[(crc >> 24) ^ *p];
64 return ~crc; /* transmit complement, per CRC-32 spec */
65 }
66
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