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/* 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 <stdint.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() = default;
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 = ~(~0u << (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::WriteULEB128(uint64_t aValue) {
// See https://en.wikipedia.org/wiki/LEB128#Encode_unsigned_integer
do {
uint8_t byte = aValue & 0x7F;
aValue >>= 7;
WriteBit(aValue != 0);
WriteBits(byte, 7);
} while (aValue != 0);
}
void BitWriter::CloseWithRbspTrailing() {
WriteBit(true);
WriteBits(0, (8 - mBitIndex) & 7);
}
void BitWriter::AdvanceBytes(uint32_t aByteOffset) {
MOZ_DIAGNOSTIC_ASSERT(mBitIndex == 0);
mPosition += aByteOffset;
}
} // namespace mozilla
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