зеркало из https://github.com/mozilla/gecko-dev.git
87 строки
2.8 KiB
C++
87 строки
2.8 KiB
C++
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#include "BitWriter.h"
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#include "MediaData.h"
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#include "mozilla/MathAlgorithms.h"
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namespace mozilla {
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constexpr uint8_t golombLen[256] = {
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1, 3, 3, 5, 5, 5, 5, 7, 7, 7, 7, 7, 7, 7, 7, 9, 9, 9, 9,
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9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 11, 11, 11, 11, 11, 11, 11,
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11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
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11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
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13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
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13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
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13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
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15, 15, 15, 15, 15, 15, 15, 15, 17,
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};
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BitWriter::BitWriter(MediaByteBuffer* aBuffer) : mBuffer(aBuffer) {}
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BitWriter::~BitWriter() {}
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void BitWriter::WriteBits(uint64_t aValue, size_t aBits) {
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MOZ_ASSERT(aBits <= sizeof(uint64_t) * 8);
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while (aBits) {
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if (mBitIndex == 0) {
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mBuffer->AppendElement(0);
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}
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const uint8_t clearMask = ~(~0 << (8 - mBitIndex));
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uint8_t mask = 0;
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if (mBitIndex + aBits > 8) {
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// Not enough bits in the current byte to write all the bits
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// required, we'll process what we can and continue with the left over.
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const uint8_t leftOverBits = mBitIndex + aBits - 8;
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const uint64_t leftOver = aValue & (~uint64_t(0) >> (8 - mBitIndex));
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mask = aValue >> leftOverBits;
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mBitIndex = 8;
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aValue = leftOver;
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aBits = leftOverBits;
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} else {
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const uint8_t offset = 8 - mBitIndex - aBits;
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mask = aValue << offset;
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mBitIndex += aBits;
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aBits = 0;
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}
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mBuffer->ElementAt(mPosition) |= mask & clearMask;
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if (mBitIndex == 8) {
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mPosition++;
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mBitIndex = 0;
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}
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}
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}
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void BitWriter::WriteUE(uint32_t aValue) {
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MOZ_ASSERT(aValue <= (UINT32_MAX - 1));
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if (aValue < 256) {
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WriteBits(aValue + 1, golombLen[aValue]);
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} else {
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const uint32_t e = FloorLog2(aValue + 1);
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WriteBits(aValue + 1, e * 2 + 1);
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}
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}
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void BitWriter::CloseWithRbspTrailing() {
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WriteBit(true);
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WriteBits(0, (8 - mBitIndex) & 7);
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}
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} // namespace mozilla
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