Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System/sys/system/IO/compression/DeflateInput.cs

@@ -0,0 +1,62 @@
+namespace System.IO.Compression {
+    using System.Diagnostics;
+
+    internal class DeflateInput {
+        private byte[] buffer;
+        private int count;
+        private int startIndex;
+
+        internal byte[] Buffer {
+            get {
+                return buffer;
+            }
+            set {
+                buffer = value;
+            }
+        }
+
+        internal int Count {
+            get {
+                return count;
+            }
+            set {
+                count = value;
+            }
+        }
+
+        internal int StartIndex {
+            get {
+                return startIndex;
+            }
+            set {
+                startIndex = value;
+            }
+        }
+
+        internal void ConsumeBytes(int n) {
+            Debug.Assert(n <= count, "Should use more bytes than what we have in the buffer");
+            startIndex += n;
+            count -= n;
+            Debug.Assert(startIndex + count <= buffer.Length, "Input buffer is in invalid state!");
+        }
+
+        internal InputState DumpState() {
+            InputState savedState;
+            savedState.count = count;
+            savedState.startIndex = startIndex;
+            return savedState;
+        }
+
+        internal void RestoreState(InputState state) {
+            count = state.count;
+            startIndex = state.startIndex;
+        }
+
+        internal struct InputState {
+            internal int count;
+            internal int startIndex;
+        }
+    }
+
+}
+