Method Optimize

Unrar4iOS/unrar/rarvm.cpp:776–840

#ifdef VM_OPTIMIZE
void RarVM::Optimize(VM_PreparedProgram *Prg)
{
  VM_PreparedCommand *Code=&Prg->Cmd[0];
  uint CodeSize=Prg->CmdCount;

  for (uint I=0;I<CodeSize;I++)
  {
    VM_PreparedCommand *Cmd=Code+I;

    // Replace universal opcodes with faster byte or word only processing
    // opcodes.
    switch(Cmd->OpCode)
    {
      case VM_MOV:
        Cmd->OpCode=Cmd->ByteMode ? VM_MOVB:VM_MOVD;
        continue;
      case VM_CMP:
        Cmd->OpCode=Cmd->ByteMode ? VM_CMPB:VM_CMPD;
        continue;
    }
    if ((VM_CmdFlags[Cmd->OpCode] & VMCF_CHFLAGS)==0)
      continue;

    // If we do not have jump commands between the current operation
    // and next command which will modify processor flags, we can replace
    // the current command with faster version which does not need to
    // modify flags.
    bool FlagsRequired=false;
    for (uint J=I+1;J<CodeSize;J++)
    {
      int Flags=VM_CmdFlags[Code[J].OpCode];
      if (Flags & (VMCF_JUMP|VMCF_PROC|VMCF_USEFLAGS))
      {
        FlagsRequired=true;
        break;
      }
      if (Flags & VMCF_CHFLAGS)
        break;
    }

    // Below we'll replace universal opcodes with faster byte or word only 
    // processing opcodes, which also do not modify processor flags to
    // provide better performance.
    if (FlagsRequired)
      continue;
    switch(Cmd->OpCode)
    {
      case VM_ADD:
        Cmd->OpCode=Cmd->ByteMode ? VM_ADDB:VM_ADDD;
        continue;
      case VM_SUB:
        Cmd->OpCode=Cmd->ByteMode ? VM_SUBB:VM_SUBD;
        continue;
      case VM_INC:
        Cmd->OpCode=Cmd->ByteMode ? VM_INCB:VM_INCD;
        continue;
      case VM_DEC:
        Cmd->OpCode=Cmd->ByteMode ? VM_DECB:VM_DECD;