question: public static byte [ ] decodeFast ( char [ ] chars , int offset , int charsLen ) { if ( charsLen == 0 ) { return new byte [ 0 ] ; } int sIx = offset , eIx = offset + charsLen - 1 ; while ( sIx < eIx && IA [ chars [ sIx ] ] < 0 ) sIx ++ ; while ( eIx > 0 && IA [ chars [ eIx ] ] < 0 ) eIx -- ; int pad = chars [ eIx ] == '=' ? ( chars [ eIx - 1 ] == '=' ? 2 : 1 ) : 0 ; int cCnt = eIx - sIx + 1 ; int sepCnt = charsLen > 76 ? ( chars [ 76 ] == '\r' ? cCnt / 78 : 0 ) << 1 : 0 ; int len = ( ( cCnt - sepCnt ) * 6 > > 3 ) - pad ; byte [ ] bytes = new byte [ len ] ; int d = 0 ; for ( int cc = 0 , eLen = ( len / 3 ) * 3 ; d < eLen ; ) { int i = IA [ chars [ sIx ++ ] ] << 18 | IA [ chars [ sIx ++ ] ] << 12 | IA [ chars [ sIx ++ ] ] << 6 | IA [ chars [ sIx ++ ] ] ; bytes [ d ++ ] = ( byte ) ( i > > 16 ) ; bytes [ d ++ ] = ( byte ) ( i > > 8 ) ; bytes [ d ++ ] = ( byte ) i ; if ( sepCnt > 0 && ++ cc == 19 ) { sIx += 2 ; cc = 0 ; } } if ( d < len ) { int i = 0 ; for ( int j = 0 ; sIx <= eIx - pad ; j ++ ) i |= IA [ chars [ sIx ++ ] ] << ( 18 - j * 6 ) ; for ( int r = 16 ; d < len ; r -= 8 ) bytes [ d ++ ] = ( byte ) ( i > > r ) ; } return bytes ; }
target:  Decodes a BASE64 encoded char array that is known to be resonably well formatted. The method is about twice as fast as #decode(char[]). The preconditions are:<br> + The array must have a line length of 76 chars OR no line separators at all (one line).<br> + Line separator must be "\r\n", as specified in RFC 2045 + The array must not contain illegal characters within the encoded string<br> + The array CAN have illegal characters at the beginning and end, those will be dealt with appropriately.<br>