Date Time Encoding

Any ideas or implementations floating about for encoding the current date including the milliseconds into the shortest possible string length?

e.g I want 31/10/2011 10:41:45 in th开发者_开发百科e shortest string possible (ideally 5 characters) - obviously decodable.

If it is impossible to get down to 5 characters, then the year is optional.

edit: it doesn't actually need to be decodable. It just needs to be a unique string.

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An time_t is 31 bits. Add 10 bits for up to 1000 milliseconds: That's 41 bits. You want 5 characters: That's 8 bits for the 1st 4 characters + 9 bits for the last one. Using Chinese ideograms, you should easily be able to find a range of 256 consecutive chars for each of the 1st 4 chars and a range of 512 for the last one.

Needless to say your encoded date will look... chinese! But it should do the trick ;-)

BTW, you don't have to stick to Chinese. You might even want to choose a different Unicode 256 chars range for each character. Of course, you'll want to find sequences of 256/512 printable chars.

Now let's say we skip the year. We're down to 86400 x 366 seconds per year = 31622400 seconds. Including millisecs : 31622400000. That's 35 bits. Great: We're down at 7 bits per character. Easy! :-)

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you can use the Ticks:

var ticks = System.DateTime.Now.Ticks;

this is a 64bit number. You get the Time back by calling:

var timeBack = new System.DateTime(ticks);

of course this are 8 bytes but I don't think you can get this more compact (easily).

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No can do: The total ms in an year (365 days) is 31,536,000,000 (=365*24*60*60*1000). You need 34.87628063 bits of information to store that value (log2 31,536,000,000). You probably meant "printable characters" BUT you would need 7 bits/character to store 35 bits in 5 characters. As an example base64 is 6 bits/character of information, so 6 characters. Ascii85 would be a little better, but still you would need around 5.5 characters, so 6 characters.

Clearly if you meant 5 BYTES, everything changes. You can store 34.84 years (in ms) in that space.

And if you meant 5 C# PRINTABLE AND UNPRINTABLE CHARACTERS (each C# character is 16 bits), then it's even better. 10 bytes! DateTime in C# is only 8 bytes and it uses ticks (they are a VERY VERY VERY small part of a second)!

BUT if you meant 5 C# PRINTABLE CHARACTERS characters, then use Serge's response. It's very good and show us that the world is a big place (and show us that why good questions are so much important: they let us see the world in new ways).

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You can use ASCII characters to represent the numbers and drop the formatting, for example:

31/10/2011 10:41:45

*/*/** *:*:*

*******

That's 7, you can drop 2 if you don't want to include the full year. Obviously the * are actual characters relating to a number, A could be 1 etc, or even use the proper ASCII codes.