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Repeating Decoration Seeds v1

Tag: boinc:minecraft@home
Published 2025-07-27 05:42:13


Hi everyone,

We've had a new CUDA app in beta for around the last 24 hrs and it seems stable enough to push it out of beta at this time.

Here's the technical explanation from the lead developer of the app, MC "PseudoGravity":

While each Minecraft world possesses a single world seed, every 16x16 chunk within the world possesses its own derived seed, known as a decoration seed. Each chunk’s decoration seed is determined by the unique combination of world seed and chunk location. This decoration seed in turn guides the generation of features such as trees, ores, and portions of structures.
The decoration seed formula is as follows:
decorationSeed = (AX + BZ) ^ worldSeed
Here, A and B are 64-bit pseudorandom odd numbers generated from the world seed and are therefore the same throughout the world. Variables X and Z are the coordinates of the chunk and are always multiples of 16. This formula is designed to ensure that each chunk within the world has a different decoration seed and thus different trees and related features.
However….
Taking a closer look at this equation reveals that the portion AX+BZ is the only part that depends on the chunk coordinates. If this subexpression produces the same value at multiple locations within the same world, then those chunks will have the same decoration seed. Specifically, if NA=MB mod 2**64 for some small integers N and M, then
A(X+N) + B(Z-M) = AX+BZ mod 2**64
and we see that the decorations seeds repeat along a line formed by (N,-M). When N and M are very small, interesting effects occur, as chunks form stripes along which identical trees and related features repeat endlessly.
Participants in this GPU-based BOINC project will exhaustively comb through all 2**64 Minecraft world seeds to uncover those in which the pseudorandom values A and B produce repeating patterns. Preliminary searches have discovered a few diagonally-repeating worlds, including several which repeat every single chunk diagonally. This full-scale search will produce a complete list of all Minecraft worlds in which decoration seeds repeat within a distance of 8 chunks, including non-45-degree angles.



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