/*

 *  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"

#include "vp8/common/common.h"

#include "vpx_dsp/vpx_dsp_common.h"

int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,

                       unsigned int source_sz, vpx_decrypt_cb decrypt_cb,

                       void *decrypt_state) {

  if (source_sz && !source) return 1;

  // To simplify calling code this fuction can be called with |source| == null

  // and |source_sz| == 0. This and vp8dx_bool_decoder_fill() are essentially

  // no-ops in this case.

  // Work around a ubsan warning with a ternary to avoid adding 0 to null.

  br->user_buffer_end = source ? source + source_sz : source;

  br->user_buffer = source;

  br->value = 0;

  br->count = -8;

  br->range = 255;

  br->decrypt_cb = decrypt_cb;

  br->decrypt_state = decrypt_state;

  /* 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 - CHAR_BIT - (count + CHAR_BIT);

  size_t bytes_left = br->user_buffer_end - bufptr;

  size_t bits_left = bytes_left * CHAR_BIT;

  int x = shift + CHAR_BIT - (int)bits_left;

  int loop_end = 0;

  unsigned char decrypted[sizeof(VP8_BD_VALUE) + 1];

  if (br->decrypt_cb) {

    size_t n = VPXMIN(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;

}