System.DateTime Bits

Question

Due to the difficulties that I faced with calling the DotNetOAuth CryptoKey constructor, I started exploring the .Net System.DateTime structure. According to what I read, this object is actually a 64-bit signed integer with “Ticks” encoded in the lower 62 bits, and Kind encoded in the upper 2 bits (IOW, this is a concatenation of 2-bit Good and 62- bit tics).

Now I wanted to actually “see” this, so I built a small C # program that created three System.DateTime objects:

    DateTime dtUtc = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Utc);
    DateTime dtLocal = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Local);
    DateTime dtU = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Unspecified);

Then I reset the ticks property for each and, as expected, they were all equal. Finally, I applied .ToBinary ()

    long bitUtc = dtUtc.ToBinary();
    long bitLocal = dtLocal.ToBinary();
    long bitU = dtU.ToBinary();

These debts were different, as expected. HOWEVER, I then tried to “check” the upper two bits to see which state corresponds to which settings, and found that the upper two bits were the same in all three. I used the following procedure to return the state of the bit:

public static bool IsBitSet<T>(this T t, int pos) where T : struct, IConvertible
{
    var value = t.ToInt64(CultureInfo.CurrentCulture);
    return (value & (1 << pos)) != 0;
}

(I got this from another post in SO) and named it like this:

    Boolean firstUtc = Class1.IsBitSet<long>(bitUtc, 63);
    Boolean secondUtc = Class1.IsBitSet<long>(bitUtc, 62);
    Boolean firstLocal = Class1.IsBitSet<long>(bitLocal, 63);
    Boolean secondLocal = Class1.IsBitSet<long>(bitLocal, 62);
    Boolean firstU = Class1.IsBitSet<long>(bitU, 63);
    Boolean secondU = Class1.IsBitSet<long>(bitU, 62);

Again, the first and second bits were set the same in all three (first it was true, second false). I do not understand this, since I THINK that they will all be different, which corresponds to different values ​​of SystemKind.

Finally, I read a little more and found (or at least it was said in one source) that MS does not serialize type information in .ToBinary (). Ok, but then why are the outputs of the .ToBinary () method all different?

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Answer 1

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, - ToBinary. , , , , ( ):

using System;

class Test
{
    static void Main()
    {
        DateTime dtUtc = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Utc);
        DateTime dtLocal = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Local);
        DateTime dtU = new System.DateTime(2014, 4, 29, 9, 10, 30, System.DateTimeKind.Unspecified);
        Console.WriteLine(dtUtc.ToBinary().ToString("X16"));
        Console.WriteLine(dtLocal.ToBinary().ToString("X16"));
        Console.WriteLine(dtU.ToBinary().ToString("X16"));
    }
}

:

48D131A200924700
88D131999ECDDF00
08D131A200924700

01, 10 00. , Marcin, .

IsBitSet , int, long. , 32, mod 64, . :

public static bool IsBitSet<T>(this T t, int pos) where T : struct, IConvertible
{
    var value = t.ToInt64(CultureInfo.CurrentCulture);
    return (value & (1L << pos)) != 0;
}

, (, , ), MS .ToBinary().

, :

using System;

class Test
{
    static void Main()
    {
        DateTime start = DateTime.UtcNow;
        Show(DateTime.SpecifyKind(start, DateTimeKind.Utc));
        Show(DateTime.SpecifyKind(start, DateTimeKind.Local));
        Show(DateTime.SpecifyKind(start, DateTimeKind.Unspecified));
    }

    static void Show(DateTime dt)
    {
        Console.WriteLine(dt.Kind);
        DateTime dt2 = DateTime.FromBinary(dt.ToBinary());
        Console.WriteLine(dt2.Kind);
        Console.WriteLine("===");
    }
}

Answer 2

ToBinary() - DateTimeKind. .NET :

public Int64 ToBinary() {
    if (Kind == DateTimeKind.Local) {
        // Local times need to be adjusted as you move from one time zone to another, 
        // just as they are when serializing in text. As such the format for local times
        // changes to store the ticks of the UTC time, but with flags that look like a 
        // local date.

        // To match serialization in text we need to be able to handle cases where
        // the UTC value would be out of range. Unused parts of the ticks range are
        // used for this, so that values just past max value are stored just past the
        // end of the maximum range, and values just below minimum value are stored
        // at the end of the ticks area, just below 2^62.
        TimeSpan offset = TimeZoneInfo.GetLocalUtcOffset(this, TimeZoneInfoOptions.NoThrowOnInvalidTime);
        Int64 ticks = Ticks;
        Int64 storedTicks = ticks - offset.Ticks;
        if (storedTicks < 0) {
            storedTicks = TicksCeiling + storedTicks;
        }
        return storedTicks | (unchecked((Int64) LocalMask));
    }
    else {
        return (Int64)dateData;
    }
}  

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