Before Minecraft Beta 1.8, when you reached about x:3000000 y:3000000, the terrain generator would freak out and begin generating broken scary land. What went on in the MC code to provoke this? Why didn't it just completely stop generating? Why does the game still break at locations very far from spawn? What is the cause of this game breaking bug?
closed as not a real question by Byte56, Trevor Powell, Tetrad♦ Sep 19 '12 at 16:10
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Everything has a limit, especially the numbers on a computer. Assuming he uses floating point numbers in most places, the precision at that point would be very low. My calculations say that it's about 0.25: http://ideone.com/xD7Tm
My guess is that position properties were added in the seed value, making it break a lot of calculations along the way.