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[0..63] of Char =
      'ABCDEFGHIJKLMNOPQRSTUVWXYZ' +
      'abcdefghijklmnopqrstuvwxyz' +
      '0123456789+/';      
DecodeTable: array[#0..#127] of Integer = (
      Byte('='), 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
      64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
      64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
      52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
      64,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
      15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
      64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
      41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64);
    type    PPacket = ^TPacket;
    TPacket = packed record
      case Integer of        0: (b0, b1, b2, b3: Byte);
        1: (i: Integer);
        2: (a: array[0..3] of Byte);
        3: (c: array[0..3] of Char);
    end;
    procedure EncodePacket(const Packet: TPacket; NumChars: Integer; OutBuf: PChar);
  begin
    OutBuf[0] := EnCodeTable[Packet.a[0] shr 2];
    OutBuf[1] := EnCodeTable[((Packet.a[0] shl 4) or (Packet.a[1] shr 4)) and $0000003f];
    if NumChars < 2 then
      OutBuf[2] := '='
    else
 OutBuf[2] := EnCodeTable[((Packet.a[1] shl 2) or (Packet.a[2] shr 6)) and $0000003f];
    if NumChars < 3 then
      OutBuf[3] := '='
    else
 OutBuf[3] := EnCodeTable[Packet.a[2] and $0000003f];
  end;
    function DecodePacket(InBuf: PChar; var nChars: Integer): TPacket;
  begin
    Result.a[0] := (DecodeTable[InBuf[0]] shl 2) or      (DecodeTable[InBuf[1]] shr 4);
    NChars := 1;
    if InBuf[2] <> '=' then
    begin
      Inc(NChars);
      Result.a[1] := Byte((DecodeTable[InBuf[1]] shl 4) or (DecodeTable[InBuf[2]] shr 2)); 
   end;
    if InBuf[3] <> '=' then
    begin
      Inc(NChars);
      Result.a[2] := Byte((DecodeTable[InBuf[2]] shl 6) or DecodeTable[InBuf[3]]);
    end;
  end;
    
procedure EncodeStream(Input, Output: TStream);
  type    PInteger = ^Integer;
  var    InBuf: array[0..509] of Byte;
    OutBuf: array[0..1023] of Char;
    BufPtr: PChar;    I, J, K, BytesRead: Integer;
    Packet: TPacket;
  begin
    K := 0;
    repeat      BytesRead := Input.Read(InBuf, SizeOf(InBuf));      I := 0;
      BufPtr := OutBuf;
      while I < BytesRead do
      begin
        if BytesRead - I < 3 then
          J := BytesRead - I
        else
 　　　　　　J := 3;
        Packet.i := 0;
        Packet.b0 := InBuf[I];
        if J > 1 then
          Packet.b1 := InBuf[I + 1];
        if J > 2 then
          Packet.b2 := InBuf[I + 2];
        EncodePacket(Packet, J, BufPtr);
        Inc(I, 3);
        Inc(BufPtr, 4);
        Inc(K, 4);
        if K > 75 then
        begin
          BufPtr[0] := #$0D;
          BufPtr[1] := #$0A;
          Inc(BufPtr, 2);
          K := 0;
        end;
      end;
      Output.Write(Outbuf, BufPtr - PChar(@OutBuf));
    until BytesRead = 0;  end;

    procedure DecodeStream(Input, Output: TStream);
  var
    InBuf: array[0..75] of Char;
    OutBuf: array[0..60] 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, 1);
        if NumRead = 1 then
        begin
          if C in ['0'..'9','A'..'Z','a'..'z','+','/','='] then
          begin
            Input.Position := Input.Position - 1;
            Break;
          end;
        end
 else
 Break;
      end;
    end; 
     
function ReadInput: Integer;
    var      WhiteFound, EndReached : Boolean;
      CntRead, Idx, IdxEnd: Integer;
    begin      
IdxEnd:= 0;      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 ['0'..'9','A'..'Z','a'..'z','+','/','=']) then
          begin
            Dec(IdxEnd);           
 if Idx < IdxEnd then
              Move(InBuf[Idx+1], 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 := 0;      
while I < BytesRead do      
begin        
Packet := DecodePacket(InBufPtr, J);        
K := 0;        
while J > 0 do        
begin          
OutBufPtr^ := Char(Packet.a[K]);          Inc(OutBufPtr);         
 Dec(J);          
Inc(K);        
end;        
Inc(InBufPtr, 4);        
Inc(I, 4);     
 end;      
Output.Write(OutBuf, OutBufPtr - PChar(@OutBuf));    

until BytesRead = 0;  
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.