Абе много сложно си го направил...
Аз бих написал нещо такова:

program Project1;



{$APPTYPE CONSOLE}



uses

  SysUtils;



var

  bytes : Array[0..20] of Byte = ($FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF, $FF,

                                  $FF, $7F, $00, $00, $E0, $FF, $FF, $FF, $FF, $FF, $FF);

  bits : Array[0..21 * 8 - 1] of Boolean;



procedure BytesToBits(bias : Integer);

var i, j, k : Integer;

begin

  k := -bias;

  if k < 0 then k := k + Length(bits);

  if k > High(bits) then k := k - Length(bits);

  for i := 0 to High(bytes) do

    for j := 0 to 7 do begin

      bits[k] := bytes[ i ] and (1 shl j) <> 0;

      k := (k + 1) mod Length(bits);

    end;

end;



procedure BitsToBytes(bias : Integer);

var i, j, k : Integer;

begin

  k := -bias;

  if k < 0 then k := k + Length(bits);

  if k > High(bits) then k := k - Length(bits);

  for i := 0 to High(bytes) do begin

    bytes[ i ] := 0;

    for j := 0 to 7 do begin

      bytes[ i ] := bytes[ i ] or (Byte(bits[k]) shl j);

      k := (k + 1) mod Length(bits);

    end;

  end;

end;



// за тест:

var i : Integer;

begin

  BytesToBits(25);

  for i := 0 to High(bits) do begin

    if i mod 21 = 0 then writeln;

    write(byte(bits[ i ]));

  end;

  BitsToBytes(25);

  writeln;

  for i := 0 to High(bytes) do begin

    write(IntToHex(bytes[ i ], 2), ' ');

  end;

  readln;

end.