Imported Upstream version 4.0.0~alpha1

Former-commit-id: 806294f5ded97629b74c85c09952f2a74fe182d9

external/referencesource/System.Web/Util/DateTimeUtil.cs

@@ -0,0 +1,52 @@
+//------------------------------------------------------------------------------
+// <copyright file="FileChangesMonitor.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+namespace System.Web.Util {
+
+    using System;
+
+    internal sealed class DateTimeUtil {
+        private DateTimeUtil() {}
+
+        const long FileTimeOffset = 504911232000000000;
+        static readonly DateTime    MinValuePlusOneDay = DateTime.MinValue.AddDays(1);
+        static readonly DateTime    MaxValueMinusOneDay = DateTime.MaxValue.AddDays(-1);
+
+        static internal DateTime FromFileTimeToUtc(long filetime) {
+            long universalTicks = filetime + FileTimeOffset;
+            // Dev10 733288: Caching: behavior change for CacheDependency when using UseMemoryCache=1
+            // ObjectCacheHost converts DateTime to a DateTimeOffset, and the conversion requires
+            // that DateTimeKind be set correctly
+            return new DateTime(universalTicks, DateTimeKind.Utc);
+        }
+
+        static internal DateTime ConvertToUniversalTime(DateTime localTime) {
+            if (localTime < MinValuePlusOneDay) {
+                return DateTime.MinValue;
+            }
+
+            if (localTime > MaxValueMinusOneDay) {
+                return DateTime.MaxValue;
+            }
+
+            return localTime.ToUniversalTime();
+        }
+
+        static internal DateTime ConvertToLocalTime(DateTime utcTime) {
+            if (utcTime < MinValuePlusOneDay) {
+                return DateTime.MinValue;
+            }
+
+            if (utcTime > MaxValueMinusOneDay) {
+                return DateTime.MaxValue;
+            }
+
+            return utcTime.ToLocalTime();
+        }
+    }
+}
+
+