What is this UTC time format?

I am parsing an XML file that has a field called UTCTime and contains the value 1311346453064. It also comes with a field called UTC that开发者_开发问答 contains the value 2011-07-22T10:54:13.064-04:00 which is a complete .Net DateTimeOffset I believe. The first field I can't figure out though. What generates a date in that way? It's too large to be a unix timestamp since it adds about 41 millenia to 1/1/1970. Any help in identifying it or how I can convert it to a datetime without using that second field would be a great help! Thanks.

It is equivalent to the unix timestamp [i.e. a straight count since 1970] but in milliseconds instead of seconds.

$ date -d @1311346453
Fri Jul 22 10:54:13 EDT 2011

Ending with 3064 made it obvious to me.

So, to convert in .NET you would use

static readonly DateTime epoch = new DateTime(1970,1,1,0,0,0,
                                              DateTimeKind.Utc);
long value = 1311346453064L;
var ts = new TimeSpan(value*TimeSpan.TicksPerMillisecond);
var dt = epoch + ts;

Or, slightly more efficiently at a cost of some readability

const long epochTicks = 621355968000000000L;
var dt = new TimeSpan(value*TimeSpan.TicksPerMillisecond+epochTicks,
                      DateTimeKind.Utc);

Note that this discards the timezone information (the offset of -04:00) in the other field.

Javascript example:

D:\ :: more > date.js
WScript.Echo( new Date().getTime() );
^Z

D:\ :: cscript date.js
1311975458665

This is the number of milliseconds since 01.01.1970.