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1 // FindSignature.cpp
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2
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3 #include "StdAfx.h"
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4
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5 #include "Common/Buffer.h"
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6
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7 #include "FindSignature.h"
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8
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9 #include "../../Common/StreamUtils.h"
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10
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11 HRESULT FindSignatureInStream(ISequentialInStream *stream,
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12 const Byte *signature, unsigned signatureSize,
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13 const UInt64 *limit, UInt64 &resPos)
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14 {
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15 resPos = 0;
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16 CByteBuffer byteBuffer2;
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17 byteBuffer2.SetCapacity(signatureSize);
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18 RINOK(ReadStream_FALSE(stream, byteBuffer2, signatureSize));
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19
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20 if (memcmp(byteBuffer2, signature, signatureSize) == 0)
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21 return S_OK;
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22
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23 const UInt32 kBufferSize = (1 << 16);
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24 CByteBuffer byteBuffer;
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25 byteBuffer.SetCapacity(kBufferSize);
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26 Byte *buffer = byteBuffer;
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27 UInt32 numPrevBytes = signatureSize - 1;
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28 memcpy(buffer, (const Byte *)byteBuffer2 + 1, numPrevBytes);
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29 resPos = 1;
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30 for (;;)
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31 {
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32 if (limit != NULL)
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33 if (resPos > *limit)
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34 return S_FALSE;
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35 do
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36 {
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37 UInt32 numReadBytes = kBufferSize - numPrevBytes;
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38 UInt32 processedSize;
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39 RINOK(stream->Read(buffer + numPrevBytes, numReadBytes, &processedSize));
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40 numPrevBytes += processedSize;
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41 if (processedSize == 0)
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42 return S_FALSE;
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43 }
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44 while (numPrevBytes < signatureSize);
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45 UInt32 numTests = numPrevBytes - signatureSize + 1;
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46 for (UInt32 pos = 0; pos < numTests; pos++)
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47 {
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48 Byte b = signature[0];
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49 for (; buffer[pos] != b && pos < numTests; pos++);
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50 if (pos == numTests)
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51 break;
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52 if (memcmp(buffer + pos, signature, signatureSize) == 0)
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53 {
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54 resPos += pos;
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55 return S_OK;
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56 }
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57 }
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58 resPos += numTests;
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59 numPrevBytes -= numTests;
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60 memmove(buffer, buffer + numTests, numPrevBytes);
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61 }
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62 }
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