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63 lines
1.7 KiB
63 lines
1.7 KiB
///////////////////////////////////////////////////////////////////////////////
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//
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// Copyright (C) 1996-1997 Microsoft Corporation. All Rights Reserved.
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//
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// MODULE: mpegcrc.c
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//
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// PURPOSE: calculate a standard MPEG 13818-1 style MSB CRC 32.
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//
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// FUNCTIONS:
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//
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// COMMENTS: Routine replaced with known good algorithm 4/9/1999 =tkb
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//
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///////////////////////////////////////////////////////////////////////////////
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#include <stdlib.h>
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#include <stdio.h>
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#include <winsock2.h>
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#include <windows.h>
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///////////////////////////////////////////////////////////////////////////////
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//
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//
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// Build crc table the first time
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//
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//
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#define MPEGCRC_POLY 0x04c11db7 // MPEG polynomial
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ULONG crc32_table[256];
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///////////////////////////////////////////////////////////////////////////////
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void
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init_mpegcrc (
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)
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///////////////////////////////////////////////////////////////////////////////
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{
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int i, j;
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ULONG 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) ^ MPEGCRC_POLY : (c << 1);
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crc32_table[i] = c;
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}
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}
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///////////////////////////////////////////////////////////////////////////////
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void
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MpegCrcUpdate (
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ULONG * crc,
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UINT len,
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UCHAR * buf
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)
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///////////////////////////////////////////////////////////////////////////////
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{
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UCHAR *p;
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if (!crc32_table[1]) /* if not already done, */
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init_mpegcrc(); /* build table */
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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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}
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