com32/libutil/unbase64.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2005-2008 H. Peter Anvin - All Rights Reserved
   4  *
   5  *   Permission is hereby granted, free of charge, to any person
   6  *   obtaining a copy of this software and associated documentation
   7  *   files (the "Software"), to deal in the Software without
   8  *   restriction, including without limitation the rights to use,
   9  *   copy, modify, merge, publish, distribute, sublicense, and/or
  10  *   sell copies of the Software, and to permit persons to whom
  11  *   the Software is furnished to do so, subject to the following
  12  *   conditions:
  13  *
  14  *   The above copyright notice and this permission notice shall
  15  *   be included in all copies or substantial portions of the Software.
  16  *
  17  *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  18  *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
  19  *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  20  *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  21  *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  22  *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  23  *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  24  *   OTHER DEALINGS IN THE SOFTWARE.
  25  *
  26  * ----------------------------------------------------------------------- */
  27
  28 /*
  29  * unbase64.c
  30  *
  31  * Convert a string in base64 format to a byte array.
  32  */
  33
  34 #include <string.h>
  35 #include <base64.h>
  36
  37 static const unsigned char _base64chars[] =
  38     "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
  39
  40 size_t unbase64(unsigned char *buffer, size_t bufsiz, const char *txt)
  41 {
  42     unsigned int bits = 0;
  43     int nbits = 0;
  44     char base64tbl[256];
  45     int i;
  46     char v;
  47     size_t nbytes = 0;
  48
  49     memset(base64tbl, -1, sizeof base64tbl);
  50
  51     for (i = 0; _base64chars[i]; i++) {
  52         base64tbl[_base64chars[i]] = i;
  53     }
  54
  55     /* Also support filesystem safe alternate base64 encoding */
  56     base64tbl['.'] = 62;
  57     base64tbl['-'] = 62;
  58     base64tbl['_'] = 63;
  59
  60     while (*txt) {
  61         if ((v = base64tbl[(unsigned char)*txt]) >= 0) {
  62             bits <<= 6;
  63             bits += v;
  64             nbits += 6;
  65             if (nbits >= 8) {
  66                 if (nbytes < bufsiz)
  67                     *buffer++ = (bits >> (nbits - 8));
  68                 nbytes++;
  69                 nbits -= 8;
  70             }
  71         }
  72         txt++;
  73     }
  74
  75     return nbytes;
  76 }