/*

 * H.265 video codec.

 * Copyright (c) 2013-2014 struktur AG, Dirk Farin <farin@struktur.de>

 *

 * This file is part of libde265.

 *

 * libde265 is free software: you can redistribute it and/or modify

 * it under the terms of 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.

 *

 * libde265 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 Lesser General Public License for more details.

 *

 * You should have received a copy of the GNU Lesser General Public License

 * along with libde265.  If not, see <http://www.gnu.org/licenses/>.

 */

#include "bitstream.h"

#include "de265.h"

#include <stdlib.h>

#include <string.h>

#include <assert.h>

void bitreader_init(bitreader* br, unsigned char* buffer, int len)

{

  br->data = buffer;

  br->bytes_remaining = len;

  br->nextbits=0;

  br->nextbits_cnt=0;

  bitreader_refill(br);

}

void bitreader_refill(bitreader* br)

{

  int shift = 64-br->nextbits_cnt;

  while (shift >= 8 && br->bytes_remaining) {

    uint64_t newval = *br->data++;

    br->bytes_remaining--;

    shift -= 8;

    newval <<= shift;

    br->nextbits |= newval;

  }

  br->nextbits_cnt = 64-shift;

}

int  get_bits(bitreader* br, int n)

{

  if (br->nextbits_cnt < n) {

    bitreader_refill(br);

  }

  uint64_t val = br->nextbits;

  val >>= 64-n;

  br->nextbits <<= n;

  br->nextbits_cnt -= n;

  return val;

}

int  get_bits_fast(bitreader* br, int n)

{

  assert(br->nextbits_cnt >= n);

  uint64_t val = br->nextbits;

  val >>= 64-n;

  br->nextbits <<= n;

  br->nextbits_cnt -= n;

  return val;

}

int  peek_bits(bitreader* br, int n)

{

  if (br->nextbits_cnt < n) {

    bitreader_refill(br);

  }

  uint64_t val = br->nextbits;

  val >>= 64-n;

  return val;

}

void skip_bits(bitreader* br, int n)

{

  if (br->nextbits_cnt < n) {

    bitreader_refill(br);

  }

  br->nextbits <<= n;

  br->nextbits_cnt -= n;

}

void skip_bits_fast(bitreader* br, int n)

{

  br->nextbits <<= n;

  br->nextbits_cnt -= n;

}

void skip_to_byte_boundary(bitreader* br)

{

  int nskip = (br->nextbits_cnt & 7);

  br->nextbits <<= nskip;

  br->nextbits_cnt -= nskip;

}

void prepare_for_CABAC(bitreader* br)

{

  skip_to_byte_boundary(br);

  int rewind = br->nextbits_cnt/8;

  br->data -= rewind;

  br->bytes_remaining += rewind;

  br->nextbits = 0;

  br->nextbits_cnt = 0;

}

int  get_uvlc(bitreader* br)

{

  int num_zeros=0;

  while (get_bits(br,1)==0) {

    num_zeros++;

    if (num_zeros > MAX_UVLC_LEADING_ZEROS) { return UVLC_ERROR; }

  }

  int offset = 0;

  if (num_zeros != 0) {

    offset = get_bits(br, num_zeros);

    int value = offset + (1<<num_zeros)-1;

    assert(value>0);

    return value;

  } else {

    return 0;

  }

}

int  get_svlc(bitreader* br)

{

  int v = get_uvlc(br);

  if (v==0) return v;

  if (v==UVLC_ERROR) return UVLC_ERROR;

  bool negative = ((v&1)==0);

  return negative ? -v/2 : (v+1)/2;

}

bool check_rbsp_trailing_bits(bitreader* br)

{

  int stop_bit = get_bits(br,1);

  assert(stop_bit==1);

  while (br->nextbits_cnt>0 || br->bytes_remaining>0) {

    int filler = get_bits(br,1);

    if (filler!=0) {

      return false;

    }

  }

  return true;

}