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xdelta3-second.h

/* xdelta 3 - delta compression tools and library
 * Copyright (C) 2002, 2003, 2006, 2007.  Joshua P. MacDonald
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of 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.
 *
 *  This program 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 a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifndef _XDELTA3_SECOND_H_
#define _XDELTA3_SECOND_H_

static inline void xd3_bit_state_encode_init (bit_state *bits)
{
  bits->cur_byte = 0;
  bits->cur_mask = 1;
}

static inline int xd3_decode_bits (xd3_stream     *stream,
                           bit_state      *bits,
                           const uint8_t **input,
                           const uint8_t  *input_max,
                           usize_t         nbits,
                           usize_t        *valuep)
{
  usize_t value = 0;
  usize_t vmask = 1 << nbits;

  if (bits->cur_mask == 0x100) { goto next_byte; }

  for (;;)
    {
      do
      {
        vmask >>= 1;

        if (bits->cur_byte & bits->cur_mask)
          {
            value |= vmask;
          }

        bits->cur_mask <<= 1;

        if (vmask == 1) { goto done; }
      }
      while (bits->cur_mask != 0x100);

    next_byte:

      if (*input == input_max)
      {
        stream->msg = "secondary decoder end of input";
        return XD3_INTERNAL;
      }

      bits->cur_byte = *(*input)++;
      bits->cur_mask = 1;
    }

 done:

  IF_DEBUG2 (DP(RINT "(d) %u ", value));

  (*valuep) = value;
  return 0;
}

#if REGRESSION_TEST
/* There may be extra bits at the end of secondary decompression, this macro
 * checks for non-zero bits.  This is overly strict, but helps pass the
 * single-bit-error regression test. */
static int
xd3_test_clean_bits (xd3_stream *stream, bit_state *bits)
{
  for (; bits->cur_mask != 0x100; bits->cur_mask <<= 1)
    {
      if (bits->cur_byte & bits->cur_mask)
      {
        stream->msg = "secondary decoder garbage";
        return XD3_INTERNAL;
      }
    }

  return 0;
}
#endif

static xd3_sec_stream*
xd3_get_secondary (xd3_stream *stream, xd3_sec_stream **sec_streamp)
{
  xd3_sec_stream *sec_stream;

  if ((sec_stream = *sec_streamp) == NULL)
    {
      if ((*sec_streamp = stream->sec_type->alloc (stream)) == NULL)
      {
        return NULL;
      }

      sec_stream = *sec_streamp;

      /* If cuumulative stats, init once. */
      stream->sec_type->init (sec_stream);
    }

  return sec_stream;
}

static int
xd3_decode_secondary (xd3_stream      *stream,
                  xd3_desect      *sect,
                  xd3_sec_stream **sec_streamp)
{
  xd3_sec_stream *sec_stream;
  uint32_t dec_size;
  uint8_t *out_used;
  int ret;

  if ((sec_stream = xd3_get_secondary (stream, sec_streamp)) == NULL)
    {
      return ENOMEM;
    }

  /* Decode the size, allocate the buffer. */
  if ((ret = xd3_read_size (stream, & sect->buf,
                      sect->buf_max, & dec_size)) ||
      (ret = xd3_decode_allocate (stream, dec_size,
                          & sect->copied2, & sect->alloc2)))
    {
      return ret;
    }

  out_used = sect->copied2;

  if ((ret = stream->sec_type->decode (stream, sec_stream,
                               & sect->buf, sect->buf_max,
                               & out_used, out_used + dec_size)))
    {
      return ret;
    }

  if (sect->buf != sect->buf_max)
    {
      stream->msg = "secondary decoder finished with unused input";
      return XD3_INTERNAL;
    }

  if (out_used != sect->copied2 + dec_size)
    {
      stream->msg = "secondary decoder short output";
      return XD3_INTERNAL;
    }

  sect->buf = sect->copied2;
  sect->buf_max = sect->copied2 + dec_size;
  sect->size = dec_size;

  return 0;
}

#if XD3_ENCODER
static inline int xd3_encode_bit (xd3_stream      *stream,
                          xd3_output     **output,
                          bit_state       *bits,
                          usize_t          bit)
{
  int ret;

  if (bit)
    {
      bits->cur_byte |= bits->cur_mask;
    }

  /* OPT: Might help to buffer more than 8 bits at once. */
  if (bits->cur_mask == 0x80)
    {
      if ((ret = xd3_emit_byte (stream, output, bits->cur_byte)) != 0)
      {
        return ret;
      }

      bits->cur_mask = 1;
      bits->cur_byte = 0;
    }
  else
    {
      bits->cur_mask <<= 1;
    }

  return 0;
}

static inline int xd3_flush_bits (xd3_stream      *stream,
                          xd3_output     **output,
                          bit_state       *bits)
{
  return (bits->cur_mask == 1) ? 0 :
    xd3_emit_byte (stream, output, bits->cur_byte);
}

static inline int xd3_encode_bits (xd3_stream      *stream,
                           xd3_output     **output,
                           bit_state       *bits,
                           usize_t           nbits,
                           usize_t           value)
{
  int ret;
  usize_t mask = 1 << nbits;

  XD3_ASSERT (nbits > 0);
  XD3_ASSERT (nbits < sizeof (usize_t) * 8);
  XD3_ASSERT (value < mask);

  do
    {
      mask >>= 1;

      if ((ret = xd3_encode_bit (stream, output, bits, value & mask)))
      {
        return ret;
      }
    }
  while (mask != 1);

  IF_DEBUG2 (DP(RINT "(e) %u ", value));

  return 0;
}

static int
xd3_encode_secondary (xd3_stream      *stream,
                  xd3_output     **head,
                  xd3_output     **tail,
                  xd3_sec_stream **sec_streamp,
                  xd3_sec_cfg     *cfg,
                  int             *did_it)
{
  xd3_sec_stream *sec_stream;
  xd3_output     *tmp_head;
  xd3_output     *tmp_tail;

  usize_t comp_size;
  usize_t orig_size;

  int ret;

  orig_size = xd3_sizeof_output (*head);

  if (orig_size < SECONDARY_MIN_INPUT) { return 0; }

  if ((sec_stream = xd3_get_secondary (stream, sec_streamp)) == NULL)
    {
      return ENOMEM;
    }

  tmp_head = xd3_alloc_output (stream, NULL);

  /* Encode the size, encode the data.  Encoding the size makes it
   * simpler, but is a little gross.  Should not need the entire
   * section in contiguous memory, but it is much easier this way. */
  if ((ret = xd3_emit_size (stream, & tmp_head, orig_size)) ||
      (ret = stream->sec_type->encode (stream, sec_stream, *head,
                               tmp_head, cfg)))
    {
      goto getout;
    }

  /* If the secondary compressor determines it's no good, it returns
   * XD3_NOSECOND. */

  /* Setup tmp_tail, comp_size */
  tmp_tail  = tmp_head;
  comp_size = tmp_head->next;

  while (tmp_tail->next_page != NULL)
    {
      tmp_tail = tmp_tail->next_page;
      comp_size += tmp_tail->next;
    }

  XD3_ASSERT (comp_size == xd3_sizeof_output (tmp_head));
  XD3_ASSERT (tmp_tail != NULL);

  if (comp_size < (orig_size - SECONDARY_MIN_SAVINGS))
    {
      IF_DEBUG1(DP(RINT "secondary saved %u bytes: %u -> %u (%0.2f%%)\n",
               orig_size - comp_size, orig_size, comp_size,
             100.0 * (double) comp_size / (double) orig_size));

      xd3_free_output (stream, *head);

      *head = tmp_head;
      *tail = tmp_tail;
      *did_it = 1;
    }
  else
    {
    getout:
      if (ret == XD3_NOSECOND) { ret = 0; }
      xd3_free_output (stream, tmp_head);
    }

  return ret;
}
#endif /* XD3_ENCODER */
#endif /* _XDELTA3_SECOND_H_ */

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