clamav/libclamunrar/unpackinline.cpp

_forceinline void Unpack::InsertOldDist(uint Distance)
{
  OldDist[3]=OldDist[2];
  OldDist[2]=OldDist[1];
  OldDist[1]=OldDist[0];
  OldDist[0]=Distance;
}

#ifdef _MSC_VER
#define FAST_MEMCPY
#endif

_forceinline void Unpack::CopyString(uint Length,uint Distance)
{
  size_t SrcPtr=UnpPtr-Distance;
  if (SrcPtr<MaxWinSize-MAX_INC_LZ_MATCH && UnpPtr<MaxWinSize-MAX_INC_LZ_MATCH)
  {
    // If we are not close to end of window, we do not need to waste time
    // to "& MaxWinMask" pointer protection.

    byte *Src=Window+SrcPtr;
    byte *Dest=Window+UnpPtr;
    UnpPtr+=Length;

#ifdef FAST_MEMCPY
    if (Distance<Length) // Overlapping strings
#endif
      while (Length>=8)
      {
        Dest[0]=Src[0];
        Dest[1]=Src[1];
        Dest[2]=Src[2];
        Dest[3]=Src[3];
        Dest[4]=Src[4];
        Dest[5]=Src[5];
        Dest[6]=Src[6];
        Dest[7]=Src[7];

        Src+=8;
        Dest+=8;
        Length-=8;
      }
#ifdef FAST_MEMCPY
    else
      while (Length>=8)
      {
        // In theory we still could overlap here.
        // Supposing Distance == MaxWinSize - 1 we have memcpy(Src, Src + 1, 8).
        // But for real RAR archives Distance <= MaxWinSize - MAX_INC_LZ_MATCH
        // always, so overlap here is impossible.

        // This memcpy expanded inline by MSVC. We could also use uint64
        // assignment, which seems to provide about the same speed.
        memcpy(Dest,Src,8); 

        Src+=8;
        Dest+=8;
        Length-=8;
      }
#endif

    // Unroll the loop for 0 - 7 bytes left. Note that we use nested "if"s.
    if (Length>0) { Dest[0]=Src[0];
    if (Length>1) { Dest[1]=Src[1];
    if (Length>2) { Dest[2]=Src[2];
    if (Length>3) { Dest[3]=Src[3];
    if (Length>4) { Dest[4]=Src[4];
    if (Length>5) { Dest[5]=Src[5];
    if (Length>6) { Dest[6]=Src[6]; } } } } } } } // Close all nested "if"s.
  }
  else
    while (Length-- > 0) // Slow copying with all possible precautions.
    {
      Window[UnpPtr]=Window[SrcPtr++ & MaxWinMask];
      // We need to have masked UnpPtr after quit from loop, so it must not
      // be replaced with 'Window[UnpPtr++ & MaxWinMask]'
      UnpPtr=(UnpPtr+1) & MaxWinMask;
    }
}


_forceinline uint Unpack::DecodeNumber(BitInput &Inp,DecodeTable *Dec)
{
  // Left aligned 15 bit length raw bit field.
  uint BitField=Inp.getbits() & 0xfffe;

  if (BitField<Dec->DecodeLen[Dec->QuickBits])
  {
    uint Code=BitField>>(16-Dec->QuickBits);
    Inp.addbits(Dec->QuickLen[Code]);
    return Dec->QuickNum[Code];
  }

  // Detect the real bit length for current code.
  uint Bits=15;
  for (uint I=Dec->QuickBits+1;I<15;I++)
    if (BitField<Dec->DecodeLen[I])
    {
      Bits=I;
      break;
    }

  Inp.addbits(Bits);
  
  // Calculate the distance from the start code for current bit length.
  uint Dist=BitField-Dec->DecodeLen[Bits-1];

  // Start codes are left aligned, but we need the normal right aligned
  // number. So we shift the distance to the right.
  Dist>>=(16-Bits);

  // Now we can calculate the position in the code list. It is the sum
  // of first position for current bit length and right aligned distance
  // between our bit field and start code for current bit length.
  uint Pos=Dec->DecodePos[Bits]+Dist;

  // Out of bounds safety check required for damaged archives.
  if (Pos>=Dec->MaxNum)
    Pos=0;

  // Convert the position in the code list to position in alphabet
  // and return it.
  return Dec->DecodeNum[Pos];
}


_forceinline uint Unpack::SlotToLength(BitInput &Inp,uint Slot)
{
  uint LBits,Length=2;
  if (Slot<8)
  {
    LBits=0;
    Length+=Slot;
  }
  else
  {
    LBits=Slot/4-1;
    Length+=(4 | (Slot & 3)) << LBits;
  }

  if (LBits>0)
  {
    Length+=Inp.getbits()>>(16-LBits);
    Inp.addbits(LBits);
  }
  return Length;
}