Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Xml/System/Xml/BinHexEncoderAsync.cs

@@ -0,0 +1,33 @@
+
+using System.Threading.Tasks;
+
+namespace System.Xml {
+    internal static partial class BinHexEncoder {
+
+        internal static async Task EncodeAsync( byte[] buffer, int index, int count, XmlWriter writer ) {
+            if ( buffer == null ) {
+                throw new ArgumentNullException( "buffer" );
+            }
+            if ( index < 0 ) {
+                throw new ArgumentOutOfRangeException( "index" );
+            }
+            if ( count < 0 ) {
+                throw new ArgumentOutOfRangeException( "count" );
+            }
+            if ( count > buffer.Length - index ) {
+                throw new ArgumentOutOfRangeException( "count" );
+            }
+
+            char[] chars = new char[ ( count * 2 ) < CharsChunkSize ? ( count * 2 ) : CharsChunkSize ];
+            int endIndex = index + count;
+            while ( index < endIndex ) {
+                int cnt = ( count < CharsChunkSize/2 ) ? count : CharsChunkSize/2;
+                int charCount = Encode( buffer, index, cnt, chars );
+                await writer.WriteRawAsync( chars, 0, charCount ).ConfigureAwait(false);
+                index += cnt;
+                count -= cnt;
+            }
+        }
+
+    } // class
+} // namespace