I'm trying to create a unique unsigned "long" number ($64$ bits) from a list of $4$ other numerical values. Some function $f(n_1, n_2, n_3, n_4) = x$. The order of the values is important so unfortunately I can't use this technique (calculating unique value from given numbers) which seems to give the same unique value from a set of numbers where order doesn't matter.
For example $n_1 = 10, n_2 = 14, n_3 = 18, n_4 = 21$ should be different than $m_1 = 10, m_2 = 1, m_3 = 418, m_4 = 19$. In addition, $o_1 = 10, o_2 = 14, o_3 = 21, o_4 = 18$ should also be different.
I realize it might not be possible to get a truly unique number due to the 64-bit limitation but if you can help me to find a number that's very unlikely to be unique, that would be very very nice:)
Other interesting suggestions that I've looked at:
Perhaps that last one could be applied three times? Since $4$ values are two pairs, each pair could generate a unique value and then the two unique values could be used in the function again?