/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "BitWriter.h"

#include "MediaData.h"

#include "mozilla/MathAlgorithms.h"

namespace mozilla

{

constexpr uint8_t golombLen[256] = {

  1,  3,  3,  5,  5,  5,  5,  7,  7,  7,  7,  7,  7,  7,  7,  9,  9,  9,  9,

  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  11, 11, 11, 11, 11, 11, 11,

  11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,

  11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,

  13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,

  13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,

  13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,

  15, 15, 15, 15, 15, 15, 15, 15, 17,

};

BitWriter::BitWriter(MediaByteBuffer* aBuffer)

  : mBuffer(aBuffer)

{

}

BitWriter::~BitWriter() {}

void

BitWriter::WriteBits(uint64_t aValue, size_t aBits)

{

  MOZ_ASSERT(aBits <= sizeof(uint64_t) * 8);

  while (aBits) {

    if (mBitIndex == 0) {

      mBuffer->AppendElement(0);

    }

    const uint8_t clearMask = ~(~0 << (8 - mBitIndex));

    uint8_t mask = 0;

    if (mBitIndex + aBits > 8) {

      // Not enough bits in the current byte to write all the bits

      // required, we'll process what we can and continue with the left over.

      const uint8_t leftOverBits = mBitIndex + aBits - 8;

      const uint64_t leftOver = aValue & (~uint64_t(0) >> (8 - mBitIndex));

      mask = aValue >> leftOverBits;

      mBitIndex = 8;

      aValue = leftOver;

      aBits = leftOverBits;

    } else {

      const uint8_t offset = 8 - mBitIndex - aBits;

      mask = aValue << offset;

      mBitIndex += aBits;

      aBits = 0;

    }

    mBuffer->ElementAt(mPosition) |= mask & clearMask;

    if (mBitIndex == 8) {

      mPosition++;

      mBitIndex = 0;

    }

  }

}

void

BitWriter::WriteUE(uint32_t aValue)

{

  MOZ_ASSERT(aValue <= (UINT32_MAX - 1));

  if (aValue < 256) {

    WriteBits(aValue + 1, golombLen[aValue]);

  } else {

    const uint32_t e = FloorLog2(aValue + 1);

    WriteBits(aValue + 1, e * 2 + 1);

  }

}

void

BitWriter::CloseWithRbspTrailing()

{

  WriteBit(true);

  WriteBits(0, (8 - mBitIndex) & 7);

}

} // namespace mozilla