Given 2 integers a and b (positive). Is there any formula / method for generating unique ID number?
note: result from f(a,b) and f(b,a) should be the same. And this solution should work fast with large amount of data. No matter it would be a scratch of PHP code or algorithm.
Example for 32-bit numbers (using left shift)
Int64Code = Max(a, b) + (Min(a, b) << 32)