How to construct a 2 bytes or short from DateTime.Now.Date only value? YYYYmmDD-CodePudding

I see some guys do following to store Date to 2 bytes only (ushort)!, not 4 bytes (int)

Assume that format yyyyMMdd: 20220521, Fit into 1 short and 1 byte. or 1 integer only. But next code I just copied it from decompiled source. (Not understand how he manipulate bits....)

In my opinion. It can be 1 byte for last digit of year (2022 will stored as 22 byte) 1 short for month, day.... But I failed to make it just 2 bytes like below example.

I don't even understand how they achieve it... I don't understand how next code works. Wish to understand how he think to do that...

   private byte[] PackDate16(DateTime date)
        {
            if (date.Year < 2000 || date.Year > 2127)
                throw new Exception("Invalid year for a 16-bit date. Allowed values are 2010-2127");
            ushort num = (ushort)(date.Year - 2000 << 9 | date.Month << 5 | date.Day);
            return new byte[2]
            {
        (byte) ((uint) num & (uint) byte.MaxValue),
        (byte) ((uint) num >> 8)
            };
        }

After do some search... I found https://bytes.com/topic/net/answers/661377-c-program-convert-2-byte-time-2-byte-date-datetime

Are there any Bit library to do that easily?

CodePudding user response：

Why don't you manipulate with bits at all if you can just add and subtract days?

private static short CompressMe(DateTime value, DateTime minDate) =>
  (short)((value - minDate).Days   short.MinValue);

private static DateTime DeCompressMe(short value, DateTime minDate) =>
  minDate.AddDays(value - short.MinValue);

For Instance:

DateTime minDate = new DateTime(2000, 1, 1);

// -24592
var result = CompressMe(new DateTime(2022, 5, 21), minDate);
// 6 June 2179
DateTime maxDate = DeCompressMe(short.MaxValue, minDate);

So far so good you can represent dates as short if they in

1 Jan 2000 .. 6 Jun 2179

period