File: base64-decode.c

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/* base64-encode.c

   Copyright (C) 2002 Niels Möller

   This file is part of GNU Nettle.

   GNU Nettle is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * the GNU General Public License as published by the Free
       Software Foundation; either version 2 of the License, or (at your
       option) any later version.

   or both in parallel, as here.

   GNU Nettle 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
   General Public License for more details.

   You should have received copies of the GNU General Public License and
   the GNU Lesser General Public License along with this program.  If
   not, see http://www.gnu.org/licenses/.
*/

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

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

#include "base64.h"

#define TABLE_INVALID -1
#define TABLE_SPACE -2
#define TABLE_END -3

void
base64_decode_init(struct base64_decode_ctx *ctx)
{
  static const signed char base64_decode_table[0x100] =
    {
      /* White space is HT, VT, FF, CR, LF and SPC */
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -2, -2, -2, -2, -1, -1, 
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
      52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -3, -1, -1,
      -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14,
      15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
      -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
      41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
      -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };

  ctx->word = ctx->bits = ctx->padding = 0;
  ctx->table = base64_decode_table;
}

int
base64_decode_single(struct base64_decode_ctx *ctx,
		     uint8_t *dst,
		     char src)
{
  int data = ctx->table[(uint8_t) src];

  switch(data)
    {
    default:
      assert(data >= 0 && data < 0x40);

      if (ctx->padding)
	return -1;
      
      ctx->word = ctx->word << 6 | data;
      ctx->bits += 6;

      if (ctx->bits >= 8)
	{
	  ctx->bits -= 8;
	  dst[0] = ctx->word >> ctx->bits;
	  return 1;
	}
      else return 0;

    case TABLE_INVALID:
      return -1;

    case TABLE_SPACE:
      return 0;
      
    case TABLE_END:
      /* There can be at most two padding characters. */
      if (!ctx->bits || ctx->padding > 2)
	return -1;
      
      if (ctx->word & ( (1<<ctx->bits) - 1))
	/* We shouldn't have any leftover bits */
	return -1;

      ctx->padding++;
      ctx->bits -= 2;
      return 0;
    }
}

int
base64_decode_update(struct base64_decode_ctx *ctx,
		     size_t *dst_length,
		     uint8_t *dst,
		     size_t src_length,
		     const char *src)
{
  size_t done;
  size_t i;

  for (i = 0, done = 0; i<src_length; i++)
    switch(base64_decode_single(ctx, dst + done, src[i]))
      {
      case -1:
	return 0;
      case 1:
	done++;
	/* Fall through */
      case 0:
	break;
      default:
	abort();
      }
  
  assert(done <= BASE64_DECODE_LENGTH(src_length));

  *dst_length = done;
  return 1;
}

int
base64_decode_final(struct base64_decode_ctx *ctx)
{
  return ctx->bits == 0;
}