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// FindSignature.cpp
#include "StdAfx.h"
#include "Common/Buffer.h"
#include "FindSignature.h"
#include "../../Common/StreamUtils.h"
HRESULT FindSignatureInStream(ISequentialInStream *stream,
const Byte *signature, unsigned signatureSize,
const UInt64 *limit, UInt64 &resPos)
{
resPos = 0;
CByteBuffer byteBuffer2;
byteBuffer2.SetCapacity(signatureSize);
RINOK(ReadStream_FALSE(stream, byteBuffer2, signatureSize));
if (memcmp(byteBuffer2, signature, signatureSize) == 0)
return S_OK;
const UInt32 kBufferSize = (1 << 16);
CByteBuffer byteBuffer;
byteBuffer.SetCapacity(kBufferSize);
Byte *buffer = byteBuffer;
UInt32 numPrevBytes = signatureSize - 1;
memcpy(buffer, (const Byte *)byteBuffer2 + 1, numPrevBytes);
resPos = 1;
for (;;)
{
if (limit != NULL)
if (resPos > *limit)
return S_FALSE;
do
{
UInt32 numReadBytes = kBufferSize - numPrevBytes;
UInt32 processedSize;
RINOK(stream->Read(buffer + numPrevBytes, numReadBytes, &processedSize));
numPrevBytes += processedSize;
if (processedSize == 0)
return S_FALSE;
}
while (numPrevBytes < signatureSize);
UInt32 numTests = numPrevBytes - signatureSize + 1;
for (UInt32 pos = 0; pos < numTests; pos++)
{
Byte b = signature[0];
for (; buffer[pos] != b && pos < numTests; pos++);
if (pos == numTests)
break;
if (memcmp(buffer + pos, signature, signatureSize) == 0)
{
resPos += pos;
return S_OK;
}
}
resPos += numTests;
numPrevBytes -= numTests;
memmove(buffer, buffer + numTests, numPrevBytes);
}
}
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