delphi – 比较大文件

我有一些文件(3-5),我需要比较：
文件1.txt有100万个字符串.
文件2.txt有1000万个字符串.
文件3.txt有500万个字符串.
所有这些文件都与文件keys.txt(万字符串)进行比较.如果当前打开的文件中的行与keys.txt中的行相同,请将此行写入output.txt(我希望您理解我的意思).

我现在有：

function Thread.checkKeys(sLine: string): boolean;
var
  SR: TStreamReader;
  line: string;
begin
  Result := false;
  SR := TStreamReader.Create(sKeyFile); // sKeyFile - Path to file keys.txt
  try
    while (not(SR.EndOfStream)) and (not(Result))do
      begin
        line := SR.ReadLine;
        if LowerCase(line) = LowerCase(sLine) then
          begin
            saveStr(sLine);
            inc(iMatch);
            Result := true;
          end;
      end;
  finally
    SR.Free;
  end;
end;

procedure Thread.saveStr(sToSave: string);
var
  fOut: TStreamWriter;
begin
  fOut := TStreamWriter.Create('output.txt',true,TEncoding.UTF8);
  try
    fOut.WriteLine(sToSave);
  finally
    fOut.Free;
  end;
end;

procedure Thread.updateFiles;
begin
  fmMain.flDone.Caption := IntToStr(iFile);
  fmMain.flMatch.Caption := IntToStr(iMatch);
end;

并循环

fInput := TStreamReader.Create(tsFiles[iCurFile]);
    while not(fInput.EndOfStream) do
      begin
        sInput := fInput.ReadLine;
        checkKeys(sInput);
      end;
    fInput.Free;
    iFile := iCurFile + 1;
    Synchronize(updateFiles);

因此,如果我将这3个文件与文件key.txt进行比较,则需要大约4个小时.如何减少比较时间？

Keys: TDictionary<string,Boolean>; 
// doesn't matter what type you use for the value,we pick Boolean since we
// have to pick something

Keys := TDictionary<string,Integer>.Create;
SR := TStreamReader.Create(sKeyFile);
try
  while not SR.EndOfStream do
    Keys.Add(LowerCase(SR.ReadLine),True); 
    // exception raised if duplicate key found
finally
  SR.Free;
end;

function Thread.checkKeys(const sLine: string): boolean;
begin
  Result := Keys.ContainsKey(LowerCase(sLine));
  if Result then 
  begin
    saveStr(sLine);
    inc(iMatch);
  end;
end;