Re: Predictable Randomness

You need to take advantage of how perl's srand works. If it's passed the same number, then all subsequent rand calls will return the same sequence of random numbers. So what I'd do is:

Generate a true random number ( srand on the time, or somesuch, then rand again), or just use time directly.
Grab the data from the SQL.
Seed srand with your random number above.
Do a 'random' sort (preferably with a class like Shuffle.pm); this should remain the same as long as the srand seed is the same.
Present needed items.
Make sure to bury the srand seed in a hidden field so that you can grab it next time.

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain

Comment on Re: Predictable Randomness

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Re: Re: Predictable Randomness by trantor (Chaplain) on Aug 13, 2001 at 21:02 UTC
Just as a side note, generating random numbers for network usage is much harder than it seems. In the above case security and true unpredictability are not fundamental, so it might be enough to feed `srand` with the current time. It's at least advisable to XOR it (the current time) with the process ID: busy Web server are likely to respond to more than one request per second, which is the resolution returned by `time` and similar. When security is a concern, this RFC can be very useful. It's an interesting reading anyway. -- TMTOWTDI	[reply] [d/l] [select]
Re (tilly) 2: Predictable Randomness by tilly (Archbishop) on Aug 13, 2001 at 21:09 UTC
trantor has a good point about the difficulty of generating random numbers. To generate your initial seed you should call rand once (as tye notes in Perl's auto srand() RE: a random sort of list, this is pretty good) or use something like Math::TrulyRandom instead. Rolling your own based on the time is frequently inadequate and better solutions are readily available.	[reply]