Merlin's Delphi Forge

MIME encoding and decoding is used when transferring binary files over the Internet. Every byte is converted to an ASCII character that can be transfered with no problems. This is the code to encode and decode using Base 64 (MIME). You can TMemo‘s and TRichEdit‘s string text via the Text property. The original code has been written by David Barton davebarton@bigfoot.com but I have optimized it a lot (for size). I have put in all the for loops and case statements.

uses
  SysUtils;
...
const
  B64Table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
...
function Base64Encode(const S: string): string;
var
  InBuf: array[0..2] of Byte;
  OutBuf: array[0..3] of Char;
  iI, iJ: Integer;
begin
  SetLength(Result, ((Length(S) + 2) div 3) * 4);
  for iI := 1 to ((Length(S) + 2) div 3) do begin
    if Length(S) < (iI * 3) then
      Move(S[(iI - 1) * 3 + 1], InBuf, Length(S) - (iI - 1) * 3)
    else
      Move(S[(iI - 1) * 3 + 1], InBuf, 3);
    OutBuf[0] := B64Table[((InBuf[0] and $FC) shr 2) + 1];
    OutBuf[1] := B64Table[(((InBuf[0] and $3) shl 4) or ((InBuf[1] and $F0) shr 4)) + 1];
    OutBuf[2] := B64Table[(((InBuf[1] and $F) shl 2) or ((InBuf[2] and $C0) shr 6)) + 1];
    OutBuf[3] := B64Table[(InBuf[2] and $3F) + 1];
    Move(OutBuf, Result[(iI - 1) * 4 + 1], 4);
  end;
  if Length(S) mod 3 = 1 then begin
    Result[Length(Result) - 1] := '=';
    Result[Length(Result)] := '=';
  end else if Length(S) mod 3 = 2 then
    Result[Length(Result)] := '=';
end;

function Base64Decode(const S: string): string;
var
  OutBuf: array[0..2] of Byte;
  InBuf : array[0..3] of Byte;
  iI, iJ: Integer;
begin
  if Length(S) mod 4 <> 0 then
    raise Exception.Create('Base64: Incorrect string format');
  SetLength(Result, ((Length(S) div 4) - 1) * 3);
  for iI := 1 to (Length(S) div 4) - 1 do begin
    Move(S[(iI - 1) * 4 + 1], InBuf, 4);
    for iJ := 0 to 3 do
      case InBuf[iJ] of
        43: InBuf[iJ] := 62;
        48..57: Inc(InBuf[iJ], 4);
        65..90: Dec(InBuf[iJ], 65);
        97..122: Dec(InBuf[iJ], 71);
      else
        InBuf[iJ] := 63;
      end;
    OutBuf[0] := (InBuf[0] shl 2) or ((InBuf[1] shr 4) and $3);
    OutBuf[1] := (InBuf[1] shl 4) or ((InBuf[2] shr 2) and $F);
    OutBuf[2] := (InBuf[2] shl 6) or (InBuf[3] and $3F);
    Move(OutBuf, Result[(iI - 1) * 3 + 1], 3);
  end;
  if Length(S) <> 0 then begin
    Move(S[Length(S) - 3], InBuf, 4);
    if InBuf[2] = 61 then begin
      for iJ := 0 to 1 do
        case InBuf[iJ] of
          43: InBuf[iJ] := 62;
          48..57: Inc(InBuf[iJ], 4);
          65..90: Dec(InBuf[iJ], 65);
          97..122: Dec(InBuf[iJ], 71);
        else
          InBuf[iJ] := 63;
        end;
      OutBuf[0] := (InBuf[0] shl 2) or ((InBuf[1] shr 4) and $3);
      Result := Result + Char(OutBuf[0]);
    end else if InBuf[3] = 61 then begin
      for iJ := 0 to 2 do
        case InBuf[iJ] of
          43: InBuf[iJ] := 62;
          48..57: Inc(InBuf[iJ], 4);
          65..90: Dec(InBuf[iJ], 65);
          97..122: Dec(InBuf[iJ], 71);
        else
          InBuf[iJ] := 63;
        end;
      OutBuf[0] := (InBuf[0] shl 2) or ((InBuf[1] shr 4) and $3);
      OutBuf[1] := (InBuf[1] shl 4) or ((InBuf[2] shr 2) and $F);
      Result := Result + Char(OutBuf[0]) + Char(OutBuf[1]);
    end else begin
      for iJ := 0 to 3 do
        case InBuf[iJ] of
          43: InBuf[iJ] := 62;
          48..57: Inc(InBuf[iJ], 4);
          65..90: Dec(InBuf[iJ], 65);
          97..122: Dec(InBuf[iJ], 71);
        else
          InBuf[iJ] := 63;
        end;
      OutBuf[0] := (InBuf[0] shl 2) or ((InBuf[1] shr 4) and $3);
      OutBuf[1] := (InBuf[1] shl 4) or ((InBuf[2] shr 2) and $F);
      OutBuf[2] := (InBuf[2] shl 6) or (InBuf[3] and $3F);
      Result := Result + Char(OutBuf[0]) + Char(OutBuf[1]) + Char(OutBuf[2]);
    end;
  end;
end;