File: base16-decode.c

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/* base16-encode.c

   Hex decoding.

   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 "base16.h"

void
base16_decode_init(struct base16_decode_ctx *ctx)
{
  ctx->word = ctx->bits = 0;
}

enum { HEX_INVALID = -1, HEX_SPACE=-2 };

static const signed char
hex_decode_table[0x80] =
  {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -2, -1, -1, -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, -1, -1, -1, -1, -1,
     0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -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, 10, 11, 12, 13, 14, 15, -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,
  };

/* Decodes a single byte. Returns amount of output (0 or 1), or -1 on
 * errors. */
int
base16_decode_single(struct base16_decode_ctx *ctx,
		     uint8_t *dst,
		     char src)
{
  /* Avoid signed char for indexing. */
  unsigned char usrc = src;
  int digit;

  if (usrc >= 0x80)
    return -1;

  digit = hex_decode_table[usrc];
  switch (digit)
    {
    case -1:
      return -1;
    case -2:
      return 0;
    default:
      assert(digit >= 0);
      assert(digit < 0x10);

      if (ctx->bits)
	{
	  *dst = (ctx->word << 4) | digit;
	  ctx->bits = 0;
	  return 1;
	}
      else
	{
	  ctx->word = digit;
	  ctx->bits = 4;
	  return 0;
	}
    }
}

int
base16_decode_update(struct base16_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 = done = 0; i<src_length; i++)
    switch(base16_decode_single(ctx, dst + done, src[i]))
      {
      case -1:
	return 0;
      case 1:
	done++;
	/* Fall through */
      case 0:
	break;
      default:
	abort();
      }
  
  assert(done <= BASE16_DECODE_LENGTH(src_length));

  *dst_length = done;
  return 1;
}

int
base16_decode_final(struct base16_decode_ctx *ctx)
{
  return ctx->bits == 0;
}