unbase64.c

linux内核

#ident "$Id$"
/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 2005 H. Peter Anvin - All Rights Reserved
 *
 *   Permission is hereby granted, free of charge, to any person
 *   obtaining a copy of this software and associated documentation
 *   files (the "Software"), to deal in the Software without
 *   restriction, including without limitation the rights to use,
 *   copy, modify, merge, publish, distribute, sublicense, and/or
 *   sell copies of the Software, and to permit persons to whom
 *   the Software is furnished to do so, subject to the following
 *   conditions:
 *   
 *   The above copyright notice and this permission notice shall
 *   be included in all copies or substantial portions of the Software.
 *   
 *   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 *   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 *   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 *   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 *   HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 *   WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 *   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 *   OTHER DEALINGS IN THE SOFTWARE.
 *
 * ----------------------------------------------------------------------- */

/*
 * unbase64.c
 *
 * Convert a string in base64 format to a byte array.
 */

#include <string.h>
#include <base64.h>

static const unsigned char _base64chars[] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

size_t unbase64(unsigned char *buffer, size_t bufsiz, const char *txt)
{
  unsigned int bits = 0;
  int nbits = 0;
  char base64tbl[256];
  int i;
  char v;
  size_t nbytes = 0;

  
  memset(base64tbl, -1, sizeof base64tbl);

  for ( i = 0 ; _base64chars[i] ; i++ ) {
    base64tbl[_base64chars[i]] = i;
  }
  
  /* Also support filesystem safe alternate base64 encoding */
  base64tbl['.'] = 62;
  base64tbl['-'] = 62;
  base64tbl['_'] = 63;

  while ( *txt ) {
    if ( (v = base64tbl[(unsigned char) *txt]) >= 0 ) {
      bits <<= 6;
      bits += v;
      nbits += 6;
      if ( nbits >= 8 ) {
	if ( nbytes < bufsiz )
	  *buffer++ = (bits >> (nbits-8));
	nbytes++;
	nbits -= 8;
      }
    }      
    txt++;
  }

  return nbytes;
}