Ensure that blocks with all bits set do not throw

Author: ds5678

AssetRipper.TextureDecoder.Tests/AstcTests.cs

@@ -77,6 +77,8 @@ private static void AssertCorrectDecompression<T>(int blockWidth, int blockHeigh
 	}
 
 	[TestCase(new byte[16] { 83, 1, 147, 104, 198, 173, 55, 116, 182, 66, 105, 11, 102, 43, 148, 125 }, 8, 8, TestName = "GetBits Should not throw in DecodeIntseq")]
+	[TestCase(new byte[16] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }, 8, 8, TestName = "Zero blocks should not throw", Description = "Blocks of all zeros are valid")]
+	[TestCase(new byte[16] { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF }, 8, 8, TestName = "0xFF blocks should not throw", Description = "Blocks with all bits set are invalid, but should be handled gracefully")]
 	public void DecodesBlockWithoutThrowing(byte[] block, int blockWidth, int blockHeight)
 	{
 		Assert.DoesNotThrow(() => AstcDecoder.DecodeASTC<ColorBGRA<byte>, byte>(block, blockWidth, blockHeight, blockWidth, blockHeight, out _));

AssetRipper.TextureDecoder/Astc/AstcDecoder.cs

@@ -883,6 +883,11 @@ private static ulong BitReverseU64(ulong d, int bits)
 		[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
 		private static int GetBits(ReadOnlySpan<byte> input, int bit, int len)
 		{
+			if (bit < 0 || input.Length * 8 < bit + len)
+			{
+				// Invalid input, but we should return something instead of throwing an exception
+				return default;
+			}
 			ReadOnlySpan<byte> slice = input[(bit / 8)..];
 			int bitBuffer;
 			if (slice.Length >= sizeof(int))