Subject: Re: [stella] Pitfall! LFSR From: Chris Wilkson <ecwilkso@xxxxxxx> Date: Mon, 3 Sep 2001 21:49:54 -0400 (EDT) |
On Mon, 30 Jul 2001, nj bloodline wrote: > What is "random scene generation" when all the scenes are in a certain > order?! There's full maps out on the net to Pifall!, so I'm assuming the > screens are always in the same order. A Linear Feedback Shift Register (LFSR) is a type of pseudo-random number generator. Most pseudo-random number generators take a starting value, called a "seed" and will produce a sequence of numbers based on an algorithm and that number. For instance, if I had a 3-bit register that always shifted to the right and loaded the XOR of bit 1 and bit 0 into bit 2, the following sequence results: OLD -> NEW --- --- 0 0 1 4 2 5 3 1 4 2 5 6 6 7 7 3 If I preload the register with a given seed number the following sequences result: SEED SEQUENCE ---- -------- 1 1, 4, 2, 5, 6, 7, 3, 1 (repeats) 6 6, 7, 3, 1, 4, 2, 5, 6 (repeats) 3 3, 1, 4, 2, 5, 6, 7, 3 (repeats) The sequence is always the same and it always repeats. It just starts in a different position each time. The one special case is zero. If the LFSR is loaded with zero, its output will be zero forever. This is a pretty simple example. It isn't reversible (try it and see what happens) but the sequence looks random (until it starts repeating). Hope that helps! -Chris - Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
Current Thread |
---|
|
<- Previous | Index | Next -> |
---|---|---|
Re: [stella] Pitfall! LFSR, nj bloodline | Thread | Re: [stella] Pitfall! LFSR, Piero Cavina |
Re: [stella] Stella at 20, nj bloodline | Date | Re: [stella] Stella at 20, Glenn Saunders |
Month |