Type
  TIPFormat = (ifV4, ifV6);
  TIPV4 = array[0..3] of byte;
  TIPV6 = array[0..15] of byte;


// accept 0.0.0.0 to 255.255.255.255
 function StrToIPV4(const S: string): TIPV4; 
var L, N, I, U : integer;
const
  CTB : array['0'..'9'] of byte = (0,1,2,3,4,5,6,7,8,9);
begin
  L := Length(S);
  Assert((L > 6) and (L < 16), 'Error : string is not IPV4.');
  I := 0;
  U := 0;
  for N := 1 to Length(S) do
  begin
    case S[N] of
      '0'..'9': begin
        case U of
          0    : result[I] := CTB[S[N]];
          1..2 : result[I] := CTB[S[N]] + (result[I]*10);
        end;
        inc(U);
        assert(U < 4, 'Error : string is not IPV4.');
      end;
      '.' : begin
         inc(I);
         U := 0;
      end;
    end;
  end;
end;

// return 0.0.0.0 to 255.255.255.255
 function IPV4ToStr(const IP: TIPV4): string; 
begin
  result := format(
   '%d.%d.%d.%d',
   [ IP[0],IP[1],IP[2],IP[3] ]
  );
end;


// accept 0000:0000:0000:0000:0000:0000:0000:0000 to ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
function StrToIPV6(const S: string): TIPV6;
var
  N,I,H,L : integer;
const
  CNTB : array['0'..'9'] of byte = (0,1,2,3,4,5,6,7,8,9);
  CHTB : array['a'..'f'] of byte = ($a,$b,$c,$d,$e,$f);
begin
  L := Length(S);
  Assert(L = 39, 'Error: string is not IPV6');
  I := 0;
  H := 0;
  for N := 1 to L do
  begin
    case S[N] of
      '0'..'9' : begin
        case H of
          0 : result[I] := CNTB[S[N]];
          1 : result[I] := (result[I] shl 4) or CNTB[S[N]];
        end;
        inc(H);
      end;
      'a'..'f' : begin
        case H of
          0 : result[I] := CHTB[S[N]];
          1 : result[I] := (result[I] shl 4) or CHTB[S[N]];
        end;
        inc(H);
      end;
    end;
    if H > 1 then
    begin
      inc(I);
      H := 0;
    end;
  end;
end;

// return 0000:0000:0000:0000:0000:0000:0000:0000 to ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff
 function IPV6ToStr(const IP: TIPV6): string;
const
  HXTSTR : array[0..$F] of char = '0123456789abcdef';
begin
  SetLength(result, 39);
  //loop unfolded
  result[1]  := HXTSTR[IP[0] shr 4];   result[2]  := HXTSTR[IP[0] and $F];
  result[3]  := HXTSTR[IP[1] shr 4];   result[4]  := HXTSTR[IP[1] and $F];
  result[5]  := ':';
  result[6]  := HXTSTR[IP[2] shr 4];   result[7]  := HXTSTR[IP[2] and $F];
  result[8]  := HXTSTR[IP[3] shr 4];   result[9]  := HXTSTR[IP[3] and $F];
  result[10] := ':';
  result[11] := HXTSTR[IP[4] shr 4];   result[12] := HXTSTR[IP[4] and $F];
  result[13] := HXTSTR[IP[5] shr 4];   result[14] := HXTSTR[IP[5] and $F];
  result[15] := ':';
  result[16] := HXTSTR[IP[6] shr 4];   result[17] := HXTSTR[IP[6] and $F];
  result[18] := HXTSTR[IP[7] shr 4];   result[19] := HXTSTR[IP[7] and $F];
  result[20] := ':';
  result[21] := HXTSTR[IP[8] shr 4];   result[22] := HXTSTR[IP[8] and $F];
  result[23] := HXTSTR[IP[9] shr 4];   result[24] := HXTSTR[IP[9] and $F];
  result[25] := ':';
  result[26] := HXTSTR[IP[10] shr 4];  result[27] := HXTSTR[IP[10] and $F];
  result[28] := HXTSTR[IP[11] shr 4];  result[29] := HXTSTR[IP[11] and $F];
  result[30] := ':';
  result[31] := HXTSTR[IP[12] shr 4];  result[32] := HXTSTR[IP[12] and $F];
  result[33] := HXTSTR[IP[13] shr 4];  result[34] := HXTSTR[IP[13] and $F];
  result[35] := ':';
  result[36] := HXTSTR[IP[14] shr 4];  result[37] := HXTSTR[IP[14] and $F];
  result[38] := HXTSTR[IP[15] shr 4];  result[39] := HXTSTR[IP[15] and $F];
end;