Fast Math Errors

For Starters

Fast Math is a performance option in the performance mod Optifine it was developed to improve FPS by optimizing sin and cos math arguments, it helps Minecraft utilize the CPU cache better to increase fps, though the increase isn't much.

Fast Math has been known to cause in game issues, same with its counterpart performance enhancer, Fast Render.

Elytra Crash

When using Fast Math with an Elytra it is known to crash the game when flying straight up or down in some cases, showing a connection lost error saying "Invalid move player packet received", it can also crash when flying while shaking your camera around(remember this for later). This Fast Math error appeared somewhere during the early 1.12.2 releases of Optifine, it was reported but wasn't fixed until the 1.13 release. The main cause of this error is an invalid number in a few lines of code that related to the math calculations for flying in an Elytra which fail when flying straight up.

Shaking Camera Crash

When using fast math and shaking your camera around while crouch jumping can cause the "Invalid move player packed received" error, and in some cases can just crash Minecraft, and in even more rare cases causes your PC to Bluescreen when using Windows 7, 10, or 11 (8 and 8.1 didn't have this error for some reason). The cause for this error is unknown but most likely has to do with mishaps in code lines like the Elytra error.

More Errors

When using some client side mods, Multiplayer or Singleplayer, fast math can cause rendering or performance issues since there is a lot of data to process and optimize, this is more common in multiplayer with many players and builds.

When in Singleplayer using mods that affect terrain or add blocks can cause game crashes or rendering issues when using Fast Math and in some cases can corrupt your Singleplayer world.

Sources

Github

My own ingame research

Other minecraft players

Written By:  Zalinkie.

Contributors:

this page is not complete, there is more info and research to come.

please message me or ping me in the MinecraftOnline Discord server if you want me to add more info to this page