Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.ServiceModel/System/ServiceModel/Channels/SafeNativeMethods.cs

@@ -0,0 +1,56 @@
+//------------------------------------------------------------
+// Copyright (c) Microsoft Corporation.  All rights reserved.
+//------------------------------------------------------------
+namespace System.ServiceModel.Channels
+{
+    using System.Runtime;
+    using System.Runtime.InteropServices;
+    using System.Runtime.Versioning;
+    using System.Security;
+    using FILETIME = System.Runtime.InteropServices.ComTypes.FILETIME;
+
+    [SuppressUnmanagedCodeSecurity]
+    internal static class SafeNativeMethods
+    {
+        public const string KERNEL32 = "kernel32.dll";
+
+        [DllImport(KERNEL32, SetLastError = false)]
+        [ResourceExposure(ResourceScope.None)]
+        static extern uint GetSystemTimeAdjustment(
+            [Out] out int adjustment,
+            [Out] out uint increment,
+            [Out] out uint adjustmentDisabled
+        );
+        
+        [DllImport(KERNEL32, SetLastError = true)]
+        [ResourceExposure(ResourceScope.None)]
+        private static extern void GetSystemTimeAsFileTime([Out] out FILETIME time);
+
+        public static void GetSystemTimeAsFileTime(out long time) {
+            FILETIME fileTime;
+            GetSystemTimeAsFileTime(out fileTime);
+            time = 0;
+            time |= (uint)fileTime.dwHighDateTime;
+            time <<= sizeof(uint) * 8;
+            time |= (uint)fileTime.dwLowDateTime;
+        }
+
+        [Fx.Tag.SecurityNote(Critical = "Calls critical method GetSystemTimeAdjustment.",
+            Safe = "Method is a SafeNativeMethod.")]
+        [SecuritySafeCritical]
+        internal static long GetSystemTimeResolution()
+        {
+            int dummyAdjustment;
+            uint increment;
+            uint dummyAdjustmentDisabled;
+
+            if (GetSystemTimeAdjustment(out dummyAdjustment, out increment, out dummyAdjustmentDisabled) != 0)
+            {
+                return (long)increment;
+            }
+
+            // Assume the default, which is around 15 milliseconds.
+            return 15 * TimeSpan.TicksPerMillisecond;
+        }
+    }
+}