Delphi 自带了 Base64 编解码的单元

Delphi 自带了 Base64 编解码的单元，叫 EncdDecd，
这名字很拗口而且不直观，估计这是一直很少人关注和知道的原因。  
这个单元提供两套四个公开函数：  对流的编解码： procedure EncodeStream(Input, Output: TStream); 
// 编码 procedure DecodeStream(Input, Output: TStream); // 解码  
// 对字符串的编解码： 
function  EncodeString(const Input: string): string; 
// 编码 
function  DecodeString(const Input: string): string;

// 解码  这几个函数在帮助中没有。应该不算是标准库中的函数。

{********************************************************}
{                                                        }
{          Borland Delphi Visual Component Library       }
{                                                        }
{ Copyright (c) 2000, 2001 Borland Software Corporation  }
{                                                        }  

{********************************************************}
 unit EncdDecd;
{ Have string use stream encoding since that logic wraps properly }
        interface    uses Classes;
    procedure EncodeStream(Input, Output: TStream);
  procedure DecodeStream(Input, Output: TStream);
  function  EncodeString(const Input: string): string;
  function  DecodeString(const Input: string): string;    implementation
    const
EncodeTable: array[..] of Char =
      'ABCDEFGHIJKLMNOPQRSTUVWXYZ' +
      'abcdefghijklmnopqrstuvwxyz' +
      '0123456789+/';      
DecodeTable: array[#..#] of Integer = (
      Byte('='), , , , , , , , , , , , , , , ,
      , , , , , , , , , , , , , , , ,
      , , , , , , , , , , , , , , , ,
      , , , , , , , , , , , , , , , ,
      ,  ,  ,  ,  ,  ,  ,  ,  ,  ,  , , , , , ,
      , , , , , , , , , , , , , , , ,
      , , , , , , , , , , , , , , , ,
      , , , , , , , , , , , , , , , );
    type    PPacket = ^TPacket;
    TPacket = packed record
      case Integer of        : (b0, b1, b2, b3: Byte);
        : (i: Integer);
        : (a: array[..] of Byte);
        : (c: array[..] of Char);
    end;
    procedure EncodePacket(const Packet: TPacket; NumChars: Integer; OutBuf: PChar);
  begin
    OutBuf[] := EnCodeTable[Packet.a[] shr ];
    OutBuf[] := EnCodeTable[((Packet.a[] shl ) or (Packet.a[] shr )) and $0000003f];
    if NumChars <  then
      OutBuf[] := '='
    else
 OutBuf[] := EnCodeTable[((Packet.a[] shl ) or (Packet.a[] shr )) and $0000003f];
    if NumChars <  then
      OutBuf[] := '='
    else
 OutBuf[] := EnCodeTable[Packet.a[] and $0000003f];
  end;
    function DecodePacket(InBuf: PChar; var nChars: Integer): TPacket;
  begin
    Result.a[] := (DecodeTable[InBuf[]] shl ) or      (DecodeTable[InBuf[]] shr );
    NChars := ;
    if InBuf[] <> '=' then
    begin
      Inc(NChars);
      Result.a[] := Byte((DecodeTable[InBuf[]] shl ) or (DecodeTable[InBuf[]] shr ));
   end;
    if InBuf[] <> '=' then
    begin
      Inc(NChars);
      Result.a[] := Byte((DecodeTable[InBuf[]] shl ) or DecodeTable[InBuf[]]);
    end;
  end;

procedure EncodeStream(Input, Output: TStream);
  type    PInteger = ^Integer;
  var    InBuf: array[..] of Byte;
    OutBuf: array[..] of Char;
    BufPtr: PChar;    I, J, K, BytesRead: Integer;
    Packet: TPacket;
  begin
    K := ;
    repeat      BytesRead := Input.Read(InBuf, SizeOf(InBuf));      I := ;
      BufPtr := OutBuf;
      while I < BytesRead do
      begin
        if BytesRead - I <  then
          J := BytesRead - I
        else
 　　　　　　J := ;
        Packet.i := ;
        Packet.b0 := InBuf[I];
        if J >  then
          Packet.b1 := InBuf[I + ];
        if J >  then
          Packet.b2 := InBuf[I + ];
        EncodePacket(Packet, J, BufPtr);
        Inc(I, );
        Inc(BufPtr, );
        Inc(K, );
        if K >  then
        begin
          BufPtr[] := #$0D;
          BufPtr[] := #$0A;
          Inc(BufPtr, );
          K := ;
        end;
      end;
      Output.Write(Outbuf, BufPtr - PChar(@OutBuf));
    until BytesRead = ;  end;

    procedure DecodeStream(Input, Output: TStream);
  var
    InBuf: array[..] of Char;
    OutBuf: array[..] of Byte;
    InBufPtr, OutBufPtr: PChar;
    I, J, K, BytesRead: Integer;
    Packet: TPacket;

      procedure SkipWhite;
    var
      C: Char;
      NumRead: Integer;
    begin
      while True do
      begin        NumRead := Input.Read(C, );
        if NumRead =  then
        begin
          if C in [''..'','A'..'Z','a'..'z','+','/','='] then
          begin
            Input.Position := Input.Position - ;
            Break;
          end;
        end
 else
 Break;
      end;
    end; 

function ReadInput: Integer;
    var      WhiteFound, EndReached : Boolean;
      CntRead, Idx, IdxEnd: Integer;
    begin
IdxEnd:= ;      repeat        WhiteFound := False;        CntRead := Input.Read(InBuf[IdxEnd], (SizeOf(InBuf)-IdxEnd));
        EndReached := CntRead < (SizeOf(InBuf)-IdxEnd);
        Idx := IdxEnd;        IdxEnd := CntRead + IdxEnd;
        while (Idx < IdxEnd) do        begin          if not (InBuf[Idx] in [''..'','A'..'Z','a'..'z','+','/','=']) then
          begin
            Dec(IdxEnd);
 if Idx < IdxEnd then
              Move(InBuf[Idx+], InBuf[Idx], IdxEnd-Idx);
            WhiteFound := True;
          end
          else
            Inc(Idx);
        end;
      until (not WhiteFound) or (EndReached);
Result := IdxEnd;
end;
begin
repeat      SkipWhite;
 {      BytesRead := Input.Read(InBuf, SizeOf(InBuf));      }
BytesRead := ReadInput;
InBufPtr := InBuf;
OutBufPtr := @OutBuf;
 I := ;
while I < BytesRead do
begin
Packet := DecodePacket(InBufPtr, J);
K := ;
while J >  do
begin
OutBufPtr^ := Char(Packet.a[K]);          Inc(OutBufPtr);
 Dec(J);
Inc(K);
end;
Inc(InBufPtr, );
Inc(I, );
 end;
Output.Write(OutBuf, OutBufPtr - PChar(@OutBuf));    

until BytesRead = ;
end;    

function EncodeString(const Input: string): string;
var    InStr, OutStr: TStringStream;
begin
InStr := TStringStream.Create(Input);
try
OutStr := TStringStream.Create('');
try
 EncodeStream(InStr, OutStr);
Result := OutStr.DataString;
finally
    OutStr.Free;
 end;
finally
InStr.Free;
end;
end;     

function DecodeString(const Input: string): string;
var    InStr, OutStr: TStringStream;
begin
InStr := TStringStream.Create(Input);
try
OutStr := TStringStream.Create('');
 try
DecodeStream(InStr, OutStr);
Result := OutStr.DataString;
finally
    OutStr.Free;
end;
finally
    InStr.Free;
end;
end;
end.