lzma/7zCrc.c
author Ryan C. Gordon <icculus@icculus.org>
Tue, 11 Apr 2006 14:33:48 +0000
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/* 7zCrc.c */
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#include "7zCrc.h"
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#define kCrcPoly 0xEDB88320
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UInt32 g_CrcTable[256];
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void InitCrcTable()
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{
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  UInt32 i;
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  for (i = 0; i < 256; i++)
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  {
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    UInt32 r = i;
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    int j;
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    for (j = 0; j < 8; j++)
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      if (r & 1) 
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        r = (r >> 1) ^ kCrcPoly;
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      else     
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        r >>= 1;
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    g_CrcTable[i] = r;
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  }
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}
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void CrcInit(UInt32 *crc) { *crc = 0xFFFFFFFF; }
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UInt32 CrcGetDigest(UInt32 *crc) { return *crc ^ 0xFFFFFFFF; } 
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void CrcUpdateByte(UInt32 *crc, Byte b)
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{
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  *crc = g_CrcTable[((Byte)(*crc)) ^ b] ^ (*crc >> 8);
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}
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void CrcUpdateUInt16(UInt32 *crc, UInt16 v)
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{
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  CrcUpdateByte(crc, (Byte)v);
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  CrcUpdateByte(crc, (Byte)(v >> 8));
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}
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void CrcUpdateUInt32(UInt32 *crc, UInt32 v)
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{
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  int i;
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  for (i = 0; i < 4; i++)
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    CrcUpdateByte(crc, (Byte)(v >> (8 * i)));
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}
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void CrcUpdateUInt64(UInt32 *crc, UInt64 v)
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{
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  int i;
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  for (i = 0; i < 8; i++)
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  {
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    CrcUpdateByte(crc, (Byte)(v));
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    v >>= 8;
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  }
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}
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void CrcUpdate(UInt32 *crc, const void *data, size_t size)
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{
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  UInt32 v = *crc;
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  const Byte *p = (const Byte *)data;
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  for (; size > 0 ; size--, p++)
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    v = g_CrcTable[((Byte)(v)) ^ *p] ^ (v >> 8);
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  *crc = v;
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}
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UInt32 CrcCalculateDigest(const void *data, size_t size)
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{
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  UInt32 crc;
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  CrcInit(&crc);
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  CrcUpdate(&crc, data, size);
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  return CrcGetDigest(&crc);
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}
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int CrcVerifyDigest(UInt32 digest, const void *data, size_t size)
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{
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  return (CrcCalculateDigest(data, size) == digest);
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}