procedure DecodeASCII85(ASource: string; var ADest: TFPVUByteArray);
var
  CurSrcPos, CurDestPos: Integer;
  lDataDWordPtr: PCardinal;
  lDataCurChar: Char;
begin
  SetLength(ADest, 0);
  CurDestPos := 0;

  CurSrcPos := 1;
  while CurSrcPos <= Length(ASource) do
  begin
    lDataCurChar := ASource[CurSrcPos];

    // Compressed block of zeroes
    if lDataCurChar = 'z' then
    begin
      SetLength(ADest, Length(ADest)+4);
      ADest[CurDestPos] := 0;
      ADest[CurDestPos+1] := 0;
      ADest[CurDestPos+2] := 0;
      ADest[CurDestPos+3] := 0;
      Inc(CurDestPos, 4);
      Inc(CurSrcPos, 1);
      Continue;
    end;

    // Common block of data: 5 input bytes generate 4 output bytes
    SetLength(ADest, Length(ADest)+4);
    lDataDWordPtr := @(ADest[CurDestPos]);
    if CurSrcPos+4 <= Length(ASource) then
    begin
      lDataDWordPtr^ := (Byte(ASource[CurSrcPos])-33)*85*85*85*85
       + (Byte(ASource[CurSrcPos+1])-33)*85*85*85 + (Byte(ASource[CurSrcPos+2])-33)*85*85
       + (Byte(ASource[CurSrcPos+3])-33)*85 + (Byte(ASource[CurSrcPos+4])-33);
      lDataDWordPtr^ := NToBE(lDataDWordPtr^);
    end
    else if CurSrcPos+3 <= Length(ASource) then
    begin
      lDataDWordPtr^ := (Byte(ASource[CurSrcPos])-33)*85*85*85*85
       + (Byte(ASource[CurSrcPos+1])-33)*85*85*85 + (Byte(ASource[CurSrcPos+2])-33)*85*85
       + (Byte(ASource[CurSrcPos+3])-33)*85 + (Byte('u')-33);
      lDataDWordPtr^ := NToBE(lDataDWordPtr^);
      SetLength(ADest, Length(ADest)-1);
    end
    else if CurSrcPos+2 <= Length(ASource) then
    begin
      lDataDWordPtr^ := (Byte(ASource[CurSrcPos])-33)*85*85*85*85
       + (Byte(ASource[CurSrcPos+1])-33)*85*85*85 + (Byte(ASource[CurSrcPos+2])-33)*85*85
       + (Byte('u')-33)*85 + (Byte('u')-33);
      lDataDWordPtr^ := NToBE(lDataDWordPtr^);
      SetLength(ADest, Length(ADest)-2);
    end
    else if CurSrcPos+1 <= Length(ASource) then
    begin
      lDataDWordPtr^ := (Byte(ASource[CurSrcPos])-33)*85*85*85*85
       + (Byte(ASource[CurSrcPos+1])-33)*85*85*85 + (Byte('u')-33)*85*85
       + (Byte('u')-33)*85 + (Byte('u')-33);
      lDataDWordPtr^ := NToBE(lDataDWordPtr^);
      SetLength(ADest, Length(ADest)-3);
    end
    else
    begin
      raise Exception.Create('[DecodeASCII85] Too few bytes remaining to decode!');
    end;

    Inc(CurDestPos, 4);
    Inc(CurSrcPos, 5);
  end;
end;