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2020-07-09 22:26 nesdori  
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again, the rng and the seed are standard. this time i would be surprised if someone gives the correct answer instantly :)

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2020-07-09 22:29 DarkStoorM  
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I think I recognize the pattern on the mid-right, just flipped... hmm :D

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2020-07-09 23:27 dustin  
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pmau rbrtu drvpmf tsmfpz miznrt od zslrm.

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2020-07-09 23:30 dustin  
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correction last word: "yslrm".

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2020-07-10 02:31 nesdori  
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 dustin , incredible! i thought that this was too hard and i already regretted teasing you with this :) how did you find the correct answer? it's not easy to see..

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2020-07-10 08:07 dustin  
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 nesdori , thanks ;d well it took me some time, the possibility just came to me sometime when i tried to find similarities to the original  
  
it happened many times that i made a cave and thought "well here, it's impossible to get bonus diamonds, is it?!". then, usually, there's someone who does get bonus diamonds and i read in the comments "well, just some standard methods i used. nothing special!" so i'll add "just some standard detective work, quite relaxing!" to this comment, just for a tiny revenge... :p ;d

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2020-07-10 10:15 nesdori  
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 dustin , i see :D there will be another cave of this series released today evening. it's actually already ready but i'll wait a bit not to give too much head start for those who are not spending office hours in an office :) the next cave will be a little bit easier than this, i guess :)

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2020-07-10 12:45 nesdori  
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the correct answer is that for all random objects, two random values are fetched and the first one is just skipped. normal 20*40 area is filled so there are 1600 random calls instead of 800. my guess what? 1 was about saving rng calls and this definitely is not :) when i thought about this idea i assumed that there would be some spots where "compacting the original cave" -effect is clearly visible but because of the rng value skipping some original objects are missing and it's very challenging to spot what's happening. i was prepared to give some hints and i was genuinely surprised that  dustin  found the answer that quickly :)

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2020-07-10 13:18 DarkStoorM  
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I'm surprised  dustin  got that :D  
  
That actually gave me an idea

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2020-07-10 15:29 Arno  
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i've just written an extensive analysis of the c64 rng at the forum thread.  
  
i translated the binary operations to mathematical expressions (like modulo and indicators). this may be useful for further investigation! :-)  
  
<a href="http://www.boulderdash.nl/forum/viewtopic.php?p=6404#6404" target="external">http://www.boulderdash.nl/forum/viewtopic.php?p=6404#6404</a>

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2020-07-10 16:00 nesdori  
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 Arno , great analysis! i actually did some analysis yesterday myself as well because i was interested to know what are the conditions that two different seed2:s become the same after the rng is called once. i realized why it happens but your mathematical equations made a few things even clearer than just by thinking them out bitwise style :)

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2020-07-10 16:59 Arno  
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thanks  nesdori ! that's great to hear. i have a few questions myself as well which i hope to explain using these formulas. :-D