Addressing byte continuations

Author: ladeak

src/CHttpServer/CHttpServer/Http3/QPackIntegerDecoder.cs

@@ -227,7 +227,7 @@ private bool TryDecodeSimd(ReadOnlySpan<byte> buffer, ref int currentIndex, out
         Debug.Assert(buffer.Length >= 32 + currentIndex);
         var vInput = Vector256.LoadUnsafe(in buffer[currentIndex]);
         var initialBits = Avx2.MoveMask(vInput);
-        var byteCount = 32 - Lzcnt.LeadingZeroCount((uint)initialBits);
+        var byteCount = BitOperations.TrailingZeroCount(~initialBits);
         int bCount = (int)byteCount;
         if (byteCount > 5 || vInput[bCount] == 0)
             ThrowDecodingException();

tests/CHttpServer.Tests/Http3/QPackIntegerDecoderTests.cs

@@ -183,6 +183,17 @@ public void Decode1337_Simd()
         Assert.Equal(1337, result);
     }
 
+    [Fact]
+    public void Decode1337_Simd_WithMoreBytes()
+    {
+        byte[] b = [0b00011111, 0b10011010, 0b00001010, 0b10001010, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+        QPackIntegerDecoder decoder = new();
+        decoder.BeginTryDecode(b[0], 5, out _);
+        var index = 1;
+        decoder.TryDecodeIntegerSimd(b, ref index, out int result);
+        Assert.Equal(1337, result);
+    }
+
     [Fact]
     public void Decode167225_Simd()
     {