ryujinx/Ryujinx.Graphics.Nvdec.H264/H264BitStreamWriter.cs

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2.8 KiB
C#
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using System;
using System.Numerics;
namespace Ryujinx.Graphics.Nvdec.H264
{
struct H264BitStreamWriter
{
private const int BufferSize = 8;
private readonly byte[] _workBuffer;
private int _offset;
private int _buffer;
private int _bufferPos;
public H264BitStreamWriter(byte[] workBuffer)
{
_workBuffer = workBuffer;
_offset = 0;
_buffer = 0;
_bufferPos = 0;
}
public void WriteBit(bool value)
{
WriteBits(value ? 1 : 0, 1);
}
public void WriteBits(int value, int valueSize)
{
int valuePos = 0;
int remaining = valueSize;
while (remaining > 0)
{
int copySize = remaining;
int free = GetFreeBufferBits();
if (copySize > free)
{
copySize = free;
}
int mask = (1 << copySize) - 1;
int srcShift = (valueSize - valuePos) - copySize;
int dstShift = (BufferSize - _bufferPos) - copySize;
_buffer |= ((value >> srcShift) & mask) << dstShift;
valuePos += copySize;
_bufferPos += copySize;
remaining -= copySize;
}
}
private int GetFreeBufferBits()
{
if (_bufferPos == BufferSize)
{
Flush();
}
return BufferSize - _bufferPos;
}
public void Flush()
{
if (_bufferPos != 0)
{
_workBuffer[_offset++] = (byte)_buffer;
_buffer = 0;
_bufferPos = 0;
}
}
public void End()
{
WriteBit(true);
Flush();
}
public Span<byte> AsSpan()
{
return new Span<byte>(_workBuffer).Slice(0, _offset);
}
public void WriteU(uint value, int valueSize) => WriteBits((int)value, valueSize);
public void WriteSe(int value) => WriteExpGolombCodedInt(value);
public void WriteUe(uint value) => WriteExpGolombCodedUInt(value);
private void WriteExpGolombCodedInt(int value)
{
int sign = value <= 0 ? 0 : 1;
if (value < 0)
{
value = -value;
}
value = (value << 1) - sign;
WriteExpGolombCodedUInt((uint)value);
}
private void WriteExpGolombCodedUInt(uint value)
{
int size = 32 - BitOperations.LeadingZeroCount(value + 1);
WriteBits(1, size);
value -= (1u << (size - 1)) - 1;
WriteBits((int)value, size - 1);
}
}
}