Delphi BASE64单元EncdDecd的修改

Delphi BASE64单元EncdDecd的修改

EncdDecd.pas两个函数声明：

procedure EncodeStream(Input, Output: TStream);
procedure DecodeStream(Input, Output: TStream);

对于Output参数，如果是TMemoryStream，效率真是太糟糕了，测试发现，编码一个5M多的文件，要十几秒钟！

但如果是TStringStream，只要0.2~0.3秒！

WHY?

因为TMemoryStream在不断地调用Write方法，不断地向Windows要求分配内存！从而导致性能下降！而TStringStream和TFileStream则没有这个问题。

怎么办？

可以一次性给TMemoryStream分配好内存空间。假设编码前的字节数为X,那麽编码后的字节数为 (X + 2) div 3 * 4

假设解码前的字节数是X,那麽解码后的字节数约为 (X + 3) div 4 * 3

关于回车换行符的修改，找到下面这段代码：

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if K > 75 then　　　　　 　　　begin 　　　　BufPtr[0] := #$0D; // 回车 　　　　BufPtr[1] := #$0A; // 换行 　　　　Inc(BufPtr, 2); 　　　　K := 0; 　　　end;

每隔76个字符，就强制回车换行。将其注释掉， 因为这其实是没什么用。将修改的单元另存为EncdDecdEx，以后就使用它了。

在编码/解码前对Output参数的TMemoryStream事先设置缓冲区大小，避免分多次向WINDOWS申请内存分配：

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uses 　　encddecdEx; 　var 　　Input,Output:TMemoryStream; 　begin 　　Input:=TMemoryStream.Create; 　　try 　　　Input.LoadFromFile('c:\aaa.txt'); 　　　Output:=TMemoryStream.Create; 　　　try 　　　　Output.Size:=(Input.Size + 2) div 3 * 4; 　　　　EncodeStream(Input,Output); 　　　finally 　　　　Output.Free; 　　　end; 　　finally 　　　Input.Free; 　　end; 　end;

　　对D7自带的BASE64单元改造后的源码：

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/// <author>cxg 2020-2-29</author> { 在编码/解码前对Output参数的TMemoryStream事先设置缓冲区大小，避免分多次向WINDOWS申请内存分配 uses 　　encddecdEx; 　var 　　Input,Output:TMemoryStream; 　begin 　　Input:=TMemoryStream.Create; 　　try 　　　Input.LoadFromFile('c:\aaa.txt'); 　　　Output:=TMemoryStream.Create; 　　　try 　　　　Output.Size:=(Input.Size + 2) div 3 * 4; 　　　　EncodeStream(Input,Output); 　　　finally 　　　　Output.Free; 　　　end; 　　finally 　　　Input.Free; 　　end; 　end; } unit base64;   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    //rem by cxg 每隔76个字符，就强制回车换行。将其注释掉 //      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.