Refactor: use DateTime.UnixEpoch

src/libraries/System.Diagnostics.EventLog/src/System/Diagnostics/EventLogEntry.cs

@@ -247,7 +247,7 @@ public DateTime TimeGenerated
         {
             get
             {
-                return beginningOfTime.AddSeconds(IntFrom(dataBuf, bufOffset + FieldOffsets.TIMEGENERATED)).ToLocalTime();
+                return DateTime.UnixEpoch.AddSeconds(IntFrom(dataBuf, bufOffset + FieldOffsets.TIMEGENERATED)).ToLocalTime();
             }
         }
 
@@ -258,7 +258,7 @@ public DateTime TimeWritten
         {
             get
             {
-                return beginningOfTime.AddSeconds(IntFrom(dataBuf, bufOffset + FieldOffsets.TIMEWRITTEN)).ToLocalTime();
+                return DateTime.UnixEpoch.AddSeconds(IntFrom(dataBuf, bufOffset + FieldOffsets.TIMEWRITTEN)).ToLocalTime();
             }
         }
 
@@ -475,7 +475,5 @@ private static class FieldOffsets
             internal const int DATAOFFSET = 52;
             internal const int RAWDATA = 56;
         }
-
-        private static readonly DateTime beginningOfTime = new DateTime(1970, 1, 1, 0, 0, 0);
     }
 }

src/libraries/System.Reflection.Metadata/src/System/Reflection/Metadata/BlobContentId.cs

@@ -119,7 +119,7 @@ public static Func<IEnumerable<Blob>, BlobContentId> GetTimeBasedProvider()
             // In the PE File Header this is a "Time/Date Stamp" whose description is "Time and date
             // the file was created in seconds since January 1st 1970 00:00:00 or 0"
             // However, when we want to make it deterministic we fill it in (later) with bits from the hash of the full PE file.
-            uint timestamp = (uint)(DateTime.UtcNow - new DateTime(1970, 1, 1)).TotalSeconds;
+            uint timestamp = (uint)DateTimeOffset.UtcNow.ToUnixTimeSeconds();
             return content => new BlobContentId(Guid.NewGuid(), timestamp);
         }