Subject: [stella] Pitfall! LFSR From: Thomas Jentzsch <tjentzsch@xxxxxx> Date: Mon, 3 Sep 2001 20:35:48 +0200 |
Hi, I'm currently disassembling Pitfall! and found something (i think) quite interesting: The game uses a one byte (what I'd call) bidirectional LFSR for random scene generation. Bidirectional means, that the process of generating the next random number is reversible. I haven't seen that type of LFSR before and thought it would not be easy or possible to do so. (The two byte LFSR used in River Raid for the same purpose seems to be different, so Carol needs some extra RAM to store the previous random number, which is necessary to restart a scene when the player dies.) The Pitfall! LFSR generates 255 values with one byte, if somebody knows a good bidirectional two byte LFSR, please let me know. I think this could be useful for new homebrew games too. You could generate huge worlds with that. Have fun! Thomas _______________________________________________________ Thomas Jentzsch | *** Every bit is sacred ! *** tjentzsch at web dot de | - Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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