Generation if a unique id of size less than 11 bytes from a string

i am developing a piece of code to generate a unique hexadecimal value from an input string. The output siz开发者_如何学编程e must be less than 11 bytes which comes as requirement.Can someone please give me an insight into this. I have done the string to binary conversion and then the hexagonal mapping which produces a combination of alphanumeric characters but the size is always greater tha 11 bytes. I also need to regenerate the input from this unique id..Is that possible.....

Thanks in adavance

If your result must be absolutely unique and your input can be any length, then your task is impossible.

Think of it that way: how many different combinations of 11 bytes are there? 256¹¹ (or 2^11*8=2⁸⁸).

That's a big number, right? Yes, but it's not big enough.

For simplicities sake we'll talk about ASCII strings only, so we have 128 different values (in reality there are many more possibilities for a character in a Java String, but the principle stays the same. For simplicities sake we also ignore that a \0 character in a String is kind of unlikely).

Now, there are 128¹³ different 13-character ASCII strings. That's 2^7*13 or 2⁹¹ different combinations. Obviously you can't have a unique id out of 2⁸⁸ possible ids for 2⁹¹ different strings.

Less than 11 bytes means maximum 10 bytes.

8^10 is 1073741824. 2^80 is a huge number.

So if you take your hexvalue, and take it modulo that number, you should fit into the 10 bytes. Convert the remainder back to hex.

Regenerating the input will not be possible. If your input is allowed to be longer than 11 bytes, it will not be possible. That would be an endless compression.