1 files changed, 121 insertions, 0 deletions
diff --git a/Ryujinx.Graphics.Nvdec.H264/H264BitStreamWriter.cs b/Ryujinx.Graphics.Nvdec.H264/H264BitStreamWriter.cs
new file mode 100644
index 00000000..c0e2357d
--- /dev/null
+++ b/Ryujinx.Graphics.Nvdec.H264/H264BitStreamWriter.cs
@@ -0,0 +1,121 @@
+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);
+        }
+    }
+}
+\ No newline at end of file