Implement VP9 loop filtering

src/Ryujinx.Graphics.Nvdec.Vp9/ReadBitBuffer.cs

@@ -0,0 +1,96 @@
+using Ryujinx.Graphics.Nvdec.Vp9.Types;
+using System;
+using System.Diagnostics;
+using System.Numerics;
+
+namespace Ryujinx.Graphics.Nvdec.Vp9
+{
+    public ref struct ReadBitBuffer
+    {
+        public ReadOnlySpan<byte> BitBuffer;
+        public ulong BitOffset;
+        public object ErrorHandlerData;
+
+        private static int GetMsb(uint n)
+        {
+            Debug.Assert(n != 0);
+            return 31 ^ BitOperations.LeadingZeroCount(n);
+        }
+
+        private static int GetUnsignedBits(uint numValues)
+        {
+            return numValues > 0 ? GetMsb(numValues) + 1 : 0;
+        }
+
+        public int DecodeUnsignedMax(int max)
+        {
+            int data = ReadLiteral(GetUnsignedBits((uint)max));
+            return data > max ? max : data;
+        }
+
+        public ulong BytesRead()
+        {
+            return (BitOffset + 7) >> 3;
+        }
+
+        public int ReadBit()
+        {
+            ulong off = BitOffset;
+            ulong p = off >> 3;
+            int q = 7 - (int)(off & 0x7);
+            if (p < (ulong)BitBuffer.Length)
+            {
+                int bit = (BitBuffer[(int)p] >> q) & 1;
+                BitOffset = off + 1;
+                return bit;
+            }
+
+            return 0;
+        }
+
+        public int ReadLiteral(int bits)
+        {
+            int value = 0, bit;
+            for (bit = bits - 1; bit >= 0; bit--)
+            {
+                value |= ReadBit() << bit;
+            }
+
+            return value;
+        }
+
+        public int ReadSignedLiteral(int bits)
+        {
+            int value = ReadLiteral(bits);
+            return ReadBit() != 0 ? -value : value;
+        }
+
+        public int ReadInvSignedLiteral(int bits)
+        {
+            return ReadSignedLiteral(bits);
+        }
+
+        public int ReadDeltaQ()
+        {
+            return ReadBit() != 0 ? ReadSignedLiteral(4) : 0;
+        }
+
+        public void ReadFrameSize(out int width, out int height)
+        {
+            width = ReadLiteral(16) + 1;
+            height = ReadLiteral(16) + 1;
+        }
+
+        public BitstreamProfile ReadProfile()
+        {
+            int profile = ReadBit();
+            profile |= ReadBit() << 1;
+            if (profile > 2)
+            {
+                profile += ReadBit();
+            }
+
+            return (BitstreamProfile)profile;
+        }
+    }
+}