Unique, random number generator

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March 23rd, 2006, 10:13 PM

shamrog12

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Unique, random number generator

I hestitate to say never but I think that this function might never produce the same unique number. I mean 0%, not just a very small likelihood. If you know of a way to improve this, please post updates.

asp Code:

Original - asp Code

Function getRandomnum()
Randomize
dim randomVar1, randomVar2, randomVar3, currDate, ip
 
if Request.ServerVariables("HTTP_X_FORWARDED_FOR") <> "" then
 ip = Request.ServerVariables("HTTP_X_FORWARDED_FOR")
else
 ip = Request.ServerVariables("REMOTE_ADDR")
end if
 
ip = Replace(ip, ".", "")
 
currDate = Replace(Now(), "/", "")
currDate = Replace(currDate, " ", "")
currDate = Replace(currDate, ":", "")
currDate = Replace(currDate, "AM", "")
currDate = Replace(currDate, "PM", "")
 
randomVar1 = (Rnd() * 1000000)
randomVar2 = Sqr(randomVar1)
randomVar3 = Round(1000000 * (randomVar1 * randomVar2))
 
getRandomnum = (currDate & randomVar3 & ip)
End Function

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March 24th, 2006, 02:19 PM

blicci

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Look at the size of the number you are returning. You can run it for a very long time and never hit the same number twice but you will eventually. It may take a while but you will. There is no such thing as a true random number generator in computers. If there is any logic behind it them it will repeat. Take slot machines for instance. They use a "random" number generator but eventually the 3 cherries will come out again and again.

Plus I can produce a "random" number that will never repeat in one line of code without any bounds

MONTH(NOW()) & DAY(NOW()) & YEAR(NOW()) & HOUR(NOW()) & MINUTE(NOW()) & SECOND(NOW())
you see it will never be 324200632651 ever again in time.

Last edited by blicci : March 24th, 2006 at 02:27 PM.

March 24th, 2006, 02:39 PM

Black&White

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Quote:

Originally Posted by blicci

Plus I can produce a "random" number that will never repeat in one line of code without any bounds

MONTH(NOW()) & DAY(NOW()) & YEAR(NOW()) & HOUR(NOW()) & MINUTE(NOW()) & SECOND(NOW())
you see it will never be 324200632651 ever again in time.

Well thats not exactly what I'd call "random" though

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March 24th, 2006, 03:01 PM

shamrog12

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Quote:

Originally Posted by blicci

This isn't random at all. Suppose you have 1000 hits/second. You're going to have 1000 of the exact same number. I think the one I posed is about as close to random as possible. For it to not be random it would have to have the same person with the same IP address submit the form over 1 million times per second. There is a 1/9999999 chance that if the person submits the form twice in one second from the same IP address would get the same number. That's good odds.

March 24th, 2006, 03:31 PM

blicci

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fine, multiply it by my IP address and it is just as random as yours is.
My point is that there is no such thing as a computer generated random number.
I certainly wouldn't use either solution to generate a unique index in my database.

March 24th, 2006, 03:45 PM

shamrog12

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Notice the 9+ digit random number generated at the end of the time and IP address.

If you are ok with your 1/9999999 odds that this could happen if the SAME computer can submit the form TWICE in 1 second then I think you could use this in your database and after a 10000 years you would find that the same number never appears. Pretty good odds huh.

March 25th, 2006, 08:23 AM

elijathegold

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You could always try this

Code:

<%guid = server.createobject("scriptlet.typelib").guid %>

Not bad for a one liner

Although it is not really random, it should be unique

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March 25th, 2006, 11:15 AM

shamrog12

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Quote:

Originally Posted by elijathegold

You could always try this

Code:

<%guid = server.createobject("scriptlet.typelib").guid %>

Not bad for a one liner

Although it is not really random, it should be unique

Could you explain this a little bit more. I'm unfamiliar with this object and what guid is. sounds cool!

March 25th, 2006, 11:47 AM

elijathegold

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A GUID is a Globally Unique IDentifier. An algorythm is run against
the current date / time and processor id to generate the identifier
you see.

A good starting place for more info

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