110 lines
2.4 KiB
C
110 lines
2.4 KiB
C
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/* ------------------------------------------------------------------------ */
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/* */
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/* Copyright (c) Microsoft Corporation, 2000-2001. All rights reserved. */
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/* Copyright (c) Andrew Kadatch, 1991-2001. All rights reserved. */
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/* */
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/* Microsoft Confidential -- do not redistribute. */
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/* */
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/* ------------------------------------------------------------------------ */
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#include "xpress.h"
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#include "xprs.h"
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/* ------------------------ CRC-32 ---------------------------- */
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/* ------ */
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static uint32 crc32_table[256];
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static int crc32_initialized = 0;
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static void crc32_init (void)
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{
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xint i, j;
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uint32 k, m = 0xedb88320L;
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if (crc32_initialized) return;
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for (i = 0; i < 256; ++i)
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{
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k = i;
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j = 8;
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do {
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if ((k&1) == 0)
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k >>= 1;
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else
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{
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k >>= 1;
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k ^= m;
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};
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--j;
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} while (j);
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crc32_table[i] = k;
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}
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crc32_initialized = 1;
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}
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static uint32 crc32 (const uchar *p, xint n, uint32 k)
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{
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uint32 *table;
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if (n <= 0)
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return (k);
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k ^= (uint32) 0xffffffffL;
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table = crc32_table;
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#define X(i) k = table[((uchar) k) ^ p[i]] ^ (k >> 8)
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if ((n -= 32) >= 0) do
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{
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X(000); X(001); X(002); X(003); X(004); X(005); X(006); X(007);
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X(010); X(011); X(012); X(013); X(014); X(015); X(016); X(017);
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X(020); X(021); X(022); X(023); X(024); X(025); X(026); X(027);
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X(030); X(031); X(032); X(033); X(034); X(035); X(036); X(037);
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p += 32;
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}
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while ((n -= 32) >= 0);
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if ((n += 32) > 0) do
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{
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X (0);
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++p;
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--n;
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}
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while (n);
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#undef X
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k ^= (uint32) 0xffffffffL;
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return (k);
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}
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int
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XPRESS_CALL
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XpressCrc32
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(
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const void *data, // beginning of data block
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int bytes, // number of bytes
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int crc // initial value
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)
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{
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if (!crc32_initialized)
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crc32_init ();
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return (crc32 (data, bytes, crc));
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}
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#if 0
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int main (void)
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{
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int i = 0;
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crc32_init ();
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printf ("{\n");
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for (;;)
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{
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printf (" 0x%08lx", (unsigned long) crc32_table[i]);
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++i;
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if (i & 3)
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printf (",");
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else if (i == 256)
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break;
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else printf (",\n");
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}
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printf ("\n}\n");
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return (0);
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}
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#endif
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