Matthew Bolan – This Minecraft Seed Makes Everything Repeat

To me the most interesting part of minecraft is a surprising depth which can be found in its level generator this interest has led me to find interesting seeds and seed finding methods for a few years now but of the seeds I found this one is by far the most visually stunning

At first glance it might seem normal but a closer inspection reveals nearly everything in the world is repeating along these small diagonals with these seeds which work in Java Edition 115 we can find infinite terrain features animals ores and really so much more I cannot recommend enough exploring one of

These seeds for yourself as each time I load one up I noticed something new and strange going on before I get into the explanation too deeply I would like to thank is your ool for helping to translate my algorithm into code captain woo Tex for helping to find cool

Features within these worlds and geo square for help making and editing this video there’s not the only cool thing I’ve done in Minecraft recently so please consider subscribing if you want to see what I’ve been up to I promise it’s at least as cool to understand why

These seeds happen we first need to understand how minecraft generates the world every world is divided into various sized regions which handle different parts of the generation depending on what is being made minecraft decides what to generate within a region based on the region coordinates put through one of the

On-screen formulas repeating seeds happens when one of these formulas keeps spitting out the same numbers for nearby regions the most famous of these repeating seeds is probably as Olaf’s infinite mineshaft caused when the random number a in this particular formula is zero we can see why this should repeat as increasing the

X-coordinate does not change the value of zero times X likewise as I pointed out a few years ago integer overflow allows us to find seeds which repeat periodically when a is a large power of two however of the six formulas I showed this is nowhere near the end of the

Story for repeating seats today I would like to focus on a new type of repetition which can affect not only mine shafts but every decorator in the game sign Dainius Lee let’s focus on the decorator seating for now we see we have a sum of the coordinates times two random numbers

A and B both of which are odd and therefore non zero thus no repetition we’ve seen before can occur here however let’s imagine what would happen if B was equal to a or equal to negative a if this were the case that a little bit of algebra shows we can expect worlds like

The one I showed in the introduction where every chunk has the same decorations as the chunk diagonal from it some further simplification is gained from the fact that the game rounds the block position to a multiple of 16 and Java random only needs a 48-bit seed so integer overflow means we care only

About the bottom 44 bits of a and B finally as the bottommost bit of a and B is always set to 1 we only need to control 43 bits of both a and B armed with this knowledge we can now delve into the algorithm unfortunately it’s hard to explain this next part unless

You have the least some knowledge of mileage modular arithmetic I have linked a decent explanation of the subject in the description but if you just pretend we are doing normals where you should be mostly fine in order to avoid sign bit complications I will focus only on the

Case where B is equal to a in this video therefore our current objective is a seed for which next long returns two consecutive numbers having identical bits 2 through 44 to find such a seed without resorting to a painfully slow brute force we need to look at how next

Long works under the hood the way Java makes random numbers has a method called next which produces 32 random bits next long uses this method twice once for its upper 32 bits and once for its lower 32 bits we need 31 out of 32 of the lower

Bits to match between two next Long’s so we will focus on seeds where this matching will occur after which checking if the upper bits work is pretty trivial for computer programs after bit of code digging in algebra we find ourselves with this equation on screen this might look frightening for

Those of you familiar with Java random n is the upper 31 bits of an internal seed and M is the lower 17 bits and the constants just come from applying next twice to a seed as M is in fact only 17 bits an algorithm suggests itselves

We can check all two to the seventeen values of M quite easily with the computer program we can then solve for n as follows for notational cleanliness we will call this expression K substituting in we have this and subtracting KN from both sides we have this this is very

Close to done we now multiply both sides by the following magic number and reduce modular tree to the 31 finally finding that 8n is equal to this expression this will have solutions provided K is divisible by 8 and will in fact yield 8 solutions for every K which is divisible

By 8 once we have this combining our found values for nm together yields an entire seat and now we simply need to test the solutions we get until we find one where all 43 desired bits match in total I ended up finding 32 seats where

A is equal to B and 32 where a is equal to negative B I would also like to mention this new infinite mineshaft seed I found recently in which negative a is equal to 13 B this repetition is a little bit more complicated to find in less nifty-looking but this seed does

Have the added bonus of being the smallest infinite mineshaft seed which is not aligned to an axis which is kind of cool I have linked all 64 repeating decorator seeds in the description along with the code that generated them as well as two diagonal infinite mineshaft seeds thank you for watching you