File: dboolhuff.c

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/*
 *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */


#include "dboolhuff.h"

int
vp8dx_start_decode (BOOL_DECODER * br,
    const unsigned char *source,
    unsigned int source_sz, vp8_decrypt_cb * decrypt_cb, void *decrypt_state)
{
  br->user_buffer_end = source + source_sz;
  br->user_buffer = source;
  br->value = 0;
  br->count = -8;
  br->range = 255;
  br->decrypt_cb = decrypt_cb;
  br->decrypt_state = decrypt_state;

  if (source_sz && !source)
    return 1;

  /* Populate the buffer */
  vp8dx_bool_decoder_fill (br);

  return 0;
}

void
vp8dx_bool_decoder_fill (BOOL_DECODER * br)
{
  const unsigned char *bufptr = br->user_buffer;
  VP8_BD_VALUE value = br->value;
  int count = br->count;
  int shift = VP8_BD_VALUE_SIZE - 8 - (count + 8);
  size_t bytes_left = br->user_buffer_end - bufptr;
  size_t bits_left = bytes_left * CHAR_BIT;
  int x = (int) (shift + CHAR_BIT - bits_left);
  int loop_end = 0;
  unsigned char decrypted[sizeof (VP8_BD_VALUE) + 1];

  if (br->decrypt_cb) {
    size_t n =
        bytes_left > sizeof (decrypted) ? sizeof (decrypted) : bytes_left;
    br->decrypt_cb (br->decrypt_state, bufptr, decrypted, (int) n);
    bufptr = decrypted;
  }

  if (x >= 0) {
    count += VP8_LOTS_OF_BITS;
    loop_end = x;
  }

  if (x < 0 || bits_left) {
    while (shift >= loop_end) {
      count += CHAR_BIT;
      value |= (VP8_BD_VALUE) * bufptr << shift;
      ++bufptr;
      ++br->user_buffer;
      shift -= CHAR_BIT;
    }
  }

  br->value = value;
  br->count = count;
}