base64-encode.c

/* base64-encode.c
 *
 */

/* nettle, low-level cryptographics library
 *
 * Copyright (C) 2002 Niels Mller
 *  
 * The nettle library is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2.1 of the License, or (at your
 * option) any later version.
 * 
 * The nettle library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
 * License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with the nettle library; see the file COPYING.LIB.  If not, write to
 * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

#if HAVE_CONFIG_H
# include "config.h"
#endif

#include <assert.h>
#include <stdlib.h>

#include "base64.h"

static const uint8_t encode_table[64] =
  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
  "abcdefghijklmnopqrstuvwxyz"
  "0123456789+/";

#define ENCODE(x) (encode_table[0x3F & (x)])

void
base64_encode_raw(uint8_t *dst, unsigned length, const uint8_t *src)
{
  const uint8_t *in = src + length;
  uint8_t *out = dst + BASE64_ENCODE_RAW_LENGTH(length);

  unsigned left_over = length % 3;

  if (left_over)
    {
      in -= left_over;
      *--out = '=';
      switch(left_over)
	{
	case 1:
	  *--out = '=';
	  *--out = ENCODE(in[0] << 4);
	  break;
	  
	case 2:
	  *--out = ENCODE( in[1] << 2);
	  *--out = ENCODE((in[0] << 4) | (in[1] >> 4));
	  break;

	default:
	  abort();
	}
      *--out = ENCODE(in[0] >> 2);
    }