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zlib.cpp

// zlib.cpp - written and placed in the public domain by Wei Dai

#include "pch.h"
#include "zlib.h"
#include "zdeflate.h"
#include "zinflate.h"

NAMESPACE_BEGIN(CryptoPP)

static const byte DEFLATE_METHOD = 8;
static const byte FDICT_FLAG = 1 << 5;

// *************************************************************

ZlibCompressor::ZlibCompressor(BufferedTransformation *outQ, unsigned int deflateLevel, unsigned int log2WindowSize)
        : Deflator(outQ, deflateLevel, log2WindowSize)
{
}

void ZlibCompressor::WritePrestreamHeader()
{
        byte cmf = DEFLATE_METHOD | ((GetLog2WindowSize()-8) << 4);
        byte flags = GetCompressionLevel() << 6;
        AttachedTransformation()->PutWord16(RoundUpToMultipleOf(cmf*256+flags, 31));
}

void ZlibCompressor::ProcessUncompressedData(const byte *inString, unsigned int length)
{
        m_adler32.Update(inString, length);
}

void ZlibCompressor::WritePoststreamTail()
{
        SecByteBlock adler32(4);
        m_adler32.Final(adler32);
        AttachedTransformation()->Put(adler32, 4);
}

unsigned int ZlibCompressor::GetCompressionLevel() const
{
        static const unsigned int deflateToCompressionLevel[] = {0, 1, 1, 1, 2, 2, 2, 2, 2, 3};
        return deflateToCompressionLevel[GetDeflateLevel()];
}

// *************************************************************

ZlibDecompressor::ZlibDecompressor(BufferedTransformation *outQueue, bool repeat)
        : Inflator(outQueue, repeat)
{
}

void ZlibDecompressor::ProcessPrestreamHeader()
{
        byte cmf;
        byte flags;

        if (!m_inQueue.Get(cmf) || !m_inQueue.Get(flags))
                throw HeaderErr();

        if ((cmf*256+flags) % 31 != 0)
                throw HeaderErr();

        if ((cmf & 0xf) != DEFLATE_METHOD)
                throw UnsupportedAlgorithm();

        if (flags & FDICT_FLAG)
                throw UnsupportedPresetDictionary();

        m_log2WindowSize = 8 + (cmf >> 4);
}

void ZlibDecompressor::ProcessDecompressedData(const byte *inString, unsigned int length)
{
        AttachedTransformation()->Put(inString, length);
        m_adler32.Update(inString, length);
}

void ZlibDecompressor::ProcessPoststreamTail()
{
        SecByteBlock adler32(4);
        if (m_inQueue.Get(adler32, 4) != 4)
                throw Adler32Err();
        if (!m_adler32.Verify(adler32))
                throw Adler32Err();
}

NAMESPACE_END

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