BitStream optimizations

Author: ds5678

AssetRipper.TextureDecoder/Bc/BcHelpers.cs

@@ -34,11 +34,9 @@ public static void DecompressBc5(ReadOnlySpan<byte> compressedBlock, Span<byte>
 
 	public static void DecompressBc6h(ReadOnlySpan<byte> compressedBlock, Span<byte> decompressedBlock, int destinationPitch, bool isSigned)
 	{
-		BitStream bstream = new()
-		{
-			low = BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock),
-			high = BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock.Slice(sizeof(ulong)))
-		};
+		BitStream bstream = new(
+			BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock),
+			BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock.Slice(sizeof(ulong))));
 		Span<uint> r = stackalloc uint[4]; // wxyz
 		Span<uint> g = stackalloc uint[4];
 		Span<uint> b = stackalloc uint[4];
@@ -559,11 +557,9 @@ static uint ReadBc6hModeBits(ref BitStream bstream)
 
 	public static void DecompressBc7(ReadOnlySpan<byte> compressedBlock, Span<byte> decompressedBlock, int destinationPitch)
 	{
-		BitStream bstream = new()
-		{
-			low = BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock),
-			high = BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock.Slice(sizeof(ulong)))
-		};
+		BitStream bstream = new(
+			BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock),
+			BinaryPrimitives.ReadUInt64LittleEndian(compressedBlock.Slice(sizeof(ulong))));
 		Span2D<uint> endpoints = new(stackalloc uint[6 * 4], 6, 4);
 		Span2D<int> indices = new(stackalloc int[4 * 4], 4, 4);
 
@@ -1081,14 +1077,4 @@ public static void SwapValues(ref uint a, ref uint b)
 	{
 		(a, b) = (b, a);
 	}
-
-	private static uint ToUnsigned(this int value)
-	{
-		return unchecked((uint)value);
-	}
-
-	private static int ToSigned(this uint value)
-	{
-		return unchecked((int)value);
-	}
 }

AssetRipper.TextureDecoder/Bc/BitStream.cs

@@ -1,45 +1,46 @@
-namespace AssetRipper.TextureDecoder.Bc;
-
-internal struct BitStream
-{
-	public ulong low;
-	public ulong high;
-	
-	public uint ReadBits(int numBits)
-	{
-		uint mask = (1u << numBits) - 1u;
-		// Read the low N bits
-		uint bits = unchecked((uint)(this.low & mask));
-
-		this.low >>= numBits;
-		// Put the low N bits of "high" into the high 64-N bits of "low".
-		this.low |= (this.high & mask) << ((sizeof(ulong) * 8) - numBits);
-		this.high >>= numBits;
-
-		return bits;
-	}
-
-	public uint ReadBit()
-	{
-		return this.ReadBits(1);
-	}
-
-	/// <summary>
-	/// Reversed bits pulling, used in BC6H decoding
-	/// </summary>
-	/// <param name="numBits"></param>
-	/// <returns></returns>
-	public uint ReadBitsReversed(int numBits)
-	{
-		uint bits = this.ReadBits(numBits);
-		// Reverse the bits.
-		uint result = 0;
-		while (numBits-- != 0)
-		{
-			result <<= 1;
-			result |= bits & 1;
-			bits >>= 1;
-		}
-		return result;
-	}
-}
+namespace AssetRipper.TextureDecoder.Bc;
+
+internal ref struct BitStream
+{
+	private ulong low;
+	private ulong high;
+
+	public BitStream(ulong low, ulong high)
+	{
+		this.low = low;
+		this.high = high;
+	}
+	
+	public uint ReadBits(int numBits)
+	{
+		uint mask = (1u << numBits) - 1u;
+		// Read the low N bits
+		uint bits = unchecked((uint)(this.low & mask));
+
+		this.low >>= numBits;
+		// Put the low N bits of "high" into the high 64-N bits of "low".
+		this.low |= (this.high & mask) << ((sizeof(ulong) * 8) - numBits);
+		this.high >>= numBits;
+
+		return bits;
+	}
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public uint ReadBit()
+	{
+		return this.ReadBits(1);
+	}
+
+	/// <summary>
+	/// Reversed bits pulling, used in BC6H decoding
+	/// </summary>
+	/// <param name="numBits"></param>
+	/// <returns></returns>
+	[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
+	public uint ReadBitsReversed(int numBits)
+	{
+		uint bits = this.ReadBits(numBits);
+		// Reverse the bits.
+		return bits.ReverseBits() >> (32 - numBits);
+	}
+}

AssetRipper.TextureDecoder/Bc/NumericExtensions.cs

@@ -0,0 +1,24 @@
+namespace AssetRipper.TextureDecoder.Bc;
+
+internal static class NumericExtensions
+{
+	public static uint ReverseBits(this uint n)
+	{
+		n = (n >> 1) & 0x55555555 | (n << 1) & 0xAAAAAAAA;
+		n = (n >> 2) & 0x33333333 | (n << 2) & 0xCCCCCCCC;
+		n = (n >> 4) & 0x0F0F0F0F | (n << 4) & 0xF0F0F0F0;
+		n = (n >> 8) & 0x00FF00FF | (n << 8) & 0xFF00FF00;
+		n = (n >> 16) & 0x0000FFFF | (n << 16) & 0xFFFF0000;
+		return n;
+	}
+
+	public static uint ToUnsigned(this int value)
+	{
+		return unchecked((uint)value);
+	}
+
+	public static int ToSigned(this uint value)
+	{
+		return unchecked((int)value);
+	}
+}