Implements BlobReader.IndexOf(byte)

src/System.Reflection.Metadata/src/System/Reflection/Internal/Utilities/MemoryBlock.cs

@@ -515,7 +515,11 @@ internal byte[] PeekBytes(int offset, int byteCount)
         internal int IndexOf(byte b, int start)
         {
             CheckBounds(start, 0);
+            return IndexOfUnchecked(b, start);
+        }
 
+        internal int IndexOfUnchecked(byte b, int start)
+        {
             byte* p = Pointer + start;
             byte* end = Pointer + Length;
             while (p < end)

src/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobReader.cs

@@ -335,6 +335,22 @@ public SignatureHeader ReadSignatureHeader()
             return new SignatureHeader(ReadByte());
         }
 
+        /// <summary>
+        /// Finds specified byte in the blob following the current position.
+        /// </summary>
+        /// <returns>
+        /// Index relative to the current position, or -1 if the byte is not found in the blob following the current position.
+        /// </returns>
+        /// <remarks>
+        /// Doesn't change the current position.
+        /// </remarks>
+        public int IndexOf(byte value)
+        {
+            int start = Offset;
+            int absoluteIndex = _block.IndexOfUnchecked(value, start);
+            return (absoluteIndex >= 0) ? absoluteIndex - start : -1;
+        }
+
         /// <summary>
         /// Reads UTF8 encoded string starting at the current position. 
         /// </summary>

src/System.Reflection.Metadata/tests/Utilities/BlobReaderTests.cs

@@ -319,5 +319,41 @@ public unsafe void ReadFromMemoryBlock()
                 Assert.Equal(bytesRead, 0);
             }
         }
+
+        [Fact]
+        public unsafe void IndexOf()
+        {
+            byte[] buffer = new byte[]
+            {
+                0xF0, 0x90, 0x8D,
+            };
+
+            fixed (byte* bufferPtr = buffer)
+            {
+                var reader = new BlobReader(bufferPtr, buffer.Length);
+
+                Assert.Equal(0, reader.IndexOf(0xF0));
+                Assert.Equal(1, reader.IndexOf(0x90));
+                Assert.Equal(2, reader.IndexOf(0x8D));
+                Assert.Equal(-1, reader.IndexOf(0x8C));
+                Assert.Equal(-1, reader.IndexOf(0));
+                Assert.Equal(-1, reader.IndexOf(0xff));
+
+                reader.ReadByte();
+                Assert.Equal(-1, reader.IndexOf(0xF0));
+                Assert.Equal(0, reader.IndexOf(0x90));
+                Assert.Equal(1, reader.IndexOf(0x8D));
+
+                reader.ReadByte();
+                Assert.Equal(-1, reader.IndexOf(0xF0));
+                Assert.Equal(-1, reader.IndexOf(0x90));
+                Assert.Equal(0, reader.IndexOf(0x8D));
+
+                reader.ReadByte();
+                Assert.Equal(-1, reader.IndexOf(0xF0));
+                Assert.Equal(-1, reader.IndexOf(0x90));
+                Assert.Equal(-1, reader.IndexOf(0x8D));
+            }
+        }
     }
 }