crossroads

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base64decode.cc (2259B)

      1 
      2 #include "sys"
      3 
      4 /* =========================================================================
      5  * The remainder of the code originates from http://base64.sourceforge.net/.
      6  * The original version was written by Bob Trower.
      7  * Adapted for C++ by me [kk]
      8  * =========================================================================
      9  */
     10 
     11 /*
     12 ** Translation Table as described in RFC1113
     13 ** Not used during decode phase
     14 static
     15 const char *xx_cb64 =   "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
     16                         "abcdefghijklmnopqrstuvwxyz"
     17                         "0123456789+/";
     18 */
     19 
     20 /*
     21 ** Translation Table to decode (created by author)
     22 */
     23 static
     24 const char *xx_cd64 =   "|$$$}rstuvwxyz{$$$$$$$>?@"
     25                         "ABCDEFGHIJKLMNOPQRSTUVW$$$$$$XYZ"
     26                         "[\\]^_`abcdefghijklmnopq";
     27 
     28 /*
     29 ** decodeblock
     30 **
     31 ** decode 4 '6-bit' characters into 3 8-bit binary bytes
     32 */
     33 static void decodeblock(char in[4], char out[4])
     34 {   
     35     out[0] = (unsigned char ) (in[0] << 2 | in[1] >> 4);
     36     out[1] = (unsigned char ) (in[1] << 4 | in[2] >> 2);
     37     out[2] = (unsigned char ) (((in[2] << 6) & 0xc0) | in[3]);
     38 }
     39 
     40 /*
     41 ** decode
     42 **
     43 ** decode a base64 encoded stream discarding padding, line breaks and noise
     44 */
     45 static
     46 string base64_decode(char const *srcstr, int srclen) {
     47     char in[4], out[4], v;
     48     int i, j, len, morechars;
     49     string decbuf;
     50     int declen = 0;
     51 
     52     /* Initialize. Only the first 3 chars of out will get overwritten. */
     53     out[3] = 0;
     54 
     55     /* Examine all characters. */
     56     j = 0;
     57     morechars = 1;
     58     while (morechars) {
     59 	for (len = 0, i = 0; i < 4 && morechars; i++) {
     60 	    v = 0;
     61 
     62 	    while (morechars && !v) {
     63 		v = (unsigned char) srcstr[j++];
     64 		if (j > srclen)
     65 		    morechars = 0;
     66                 v = (unsigned char) ((v < 43 || v > 122) ?
     67 				     0 :
     68 				     xx_cd64[v - 43]);
     69                 if (v)
     70                     v = (unsigned char) ((v == '$') ? 0 : v - 61);
     71 	    }
     72 	    if (morechars) {
     73 		len++;
     74 		if (v)
     75 		    in[i] = (unsigned char) (v - 1);
     76 	    }
     77 	    else
     78 		in[i] = 0;
     79 	}
     80 	if (len) {
     81 	    decodeblock (in, out);
     82 	    decbuf += string(out);
     83 	    declen += len - 1;
     84 	}
     85     }
     86 
     87     /* All done. */
     88     return (decbuf);
     89 }
     90 
     91 string base64_decode(string const &s) {
     92     return base64_decode(s.c_str(), s.length());
     93 }