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
  50   memset(base64tbl, -1, sizeof base64tbl);
  51
  52   for ( i = 0 ; _base64chars[i] ; i++ ) {
  53     base64tbl[_base64chars[i]] = i;
  54   }
  55
  56   /* Also support filesystem safe alternate base64 encoding */
  57   base64tbl['.'] = 62;
  58   base64tbl['-'] = 62;
  59   base64tbl['_'] = 63;
  60
  61   while ( *txt ) {
  62     if ( (v = base64tbl[(unsigned char) *txt]) >= 0 ) {
  63       bits <<= 6;
  64       bits += v;
  65       nbits += 6;
  66       if ( nbits >= 8 ) {
  67         if ( nbytes < bufsiz )
  68           *buffer++ = (bits >> (nbits-8));
  69         nbytes++;
  70         nbits -= 8;
  71       }
  72     }
  73     txt++;
  74   }
  75
  76   return nbytes;
  77 }