text: // zlib.cpp - originally written and placed in the public domain by Wei Dai
  
  // "zlib" is the name of a well known C language compression library
  // (http://www.zlib.org) and also the name of a compression format
  // (RFC 1950) that the library implements. This file is part of a
  // complete reimplementation of the zlib compression format.
  
  #include "pch.h"
  #include "zlib.h"
  #include "zdeflate.h"
  #include "zinflate.h"
  #include "secblock.h"
  
  NAMESPACE_BEGIN(CryptoPP)
  
  static const byte DEFLATE_METHOD = 8;
  static const byte FDICT_FLAG = (1 << 5);
  
  // *************************************************************
  
  void ZlibCompressor::WritePrestreamHeader()
  {
  	m_adler32.Restart();
  	CRYPTOPP_ASSERT(((GetLog2WindowSize()-8) << 4) <= 255);
  	byte cmf = byte(DEFLATE_METHOD | ((GetLog2WindowSize()-8) << 4));
  	CRYPTOPP_ASSERT((GetCompressionLevel() << 6) <= 255);
  	byte flags = byte(GetCompressionLevel() << 6);
  	AttachedTransformation()->PutWord16(RoundUpToMultipleOf(word16(cmf*256+flags), word16(31)));
  }
  
  void ZlibCompressor::ProcessUncompressedData(const byte *inString, size_t length)
  {
  	m_adler32.Update(inString, length);
  }
  
  void ZlibCompressor::WritePoststreamTail()
  {
  	FixedSizeSecBlock<byte, 4> adler32;
  	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 *attachment, bool repeat, int propagation)
  	: Inflator(attachment, repeat, propagation), m_log2WindowSize(0)
  {
  }
  
  void ZlibDecompressor::ProcessPrestreamHeader()
  {
  	m_adler32.Restart();
  
  	byte cmf;
  	byte flags;
  
  	if (!m_inQueue.Get(cmf) || !m_inQueue.Get(flags))
  		throw HeaderErr();
  
  	if ((cmf*256+flags) % 31 != 0)
  		throw HeaderErr();	// if you hit this exception, you're probably trying to decompress invalid data
  
  	if ((cmf & 0xf) != DEFLATE_METHOD)
  		throw UnsupportedAlgorithm();
  
  	if (flags & FDICT_FLAG)
  		throw UnsupportedPresetDictionary();
  
  	m_log2WindowSize = 8 + (cmf >> 4);
  }
  
  void ZlibDecompressor::ProcessDecompressedData(const byte *inString, size_t length)
  {
  	AttachedTransformation()->Put(inString, length);
  	m_adler32.Update(inString, length);
  }
  
  void ZlibDecompressor::ProcessPoststreamTail()
  {
  	FixedSizeSecBlock<byte, 4> adler32;
  	if (m_inQueue.Get(adler32, 4) != 4)
  		throw Adler32Err();
  	if (!m_adler32.Verify(adler32))
  		throw Adler32Err();
  }
  
  NAMESPACE_END
  