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in reply to Re: Random 1-1 mapping
in thread Random 1-1 mapping

Update: Your solution is cool but $max is not guaranteed to be a power of 2. In fact, it almost certainly isn't.

I just scribbled this on a piece of paper, I think I heard something about it to do with the RSA encryption algorithm once...

$result = ($prime_number * $input + $seed) % $max;

Example for $max = 10, $prime_number = 7 and $seed = 5..

shuffle(5,10,0) == (7 * 0 + 5) % 10 == 5 % 10 == 5 shuffle(5,10,1) == (7 * 1 + 5) % 10 == 12 % 10 == 2 shuffle(5,10,2) == (7 * 2 + 5) % 10 == 19 % 10 == 9 shuffle(5,10,3) == (7 * 3 + 5) % 10 == 26 % 10 == 6 shuffle(5,10,4) == (7 * 4 + 5) % 10 == 33 % 10 == 3 shuffle(5,10,5) == (7 * 5 + 5) % 10 == 40 % 10 == 0 shuffle(5,10,6) == (7 * 6 + 5) % 10 == 47 % 10 == 7 shuffle(5,10,7) == (7 * 7 + 5) % 10 == 54 % 10 == 4 shuffle(5,10,8) == (7 * 8 + 5) % 10 == 61 % 10 == 1 shuffle(5,10,9) == (7 * 9 + 5) % 10 == 68 % 10 == 8

So that works for 7 and 10. Does it work for any $max and any $prime_number? If not what conditions will it work for? I am no good with proofs.

-Andrew.


Andrew Tomazos  |  andrew@tomazos.com  |  www.tomazos.com