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  1. Minecraft: Java Edition
  2. MC-118857

Effect amplifier is read/written as byte from NBT despite being stored as an integer

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    • Icon: Bug Bug
    • Resolution: Fixed
    • 24w05b
    • Minecraft 1.12, Minecraft 1.12.1 Pre-Release 1, Minecraft 1.12.1, Minecraft 17w50a, Minecraft 1.13.2, Minecraft 19w04b, 1.16.4, 20w46a, 21w06a, 21w16a, 21w17a, 1.17, 1.17.1 Pre-release 2, 1.17.1, 21w44a, 1.18.1, 1.18.2, 1.19, 1.19.1 Pre-release 4, 1.19.2, 1.19.3, 23w03a, 1.19.4 Pre-release 2, 1.19.4, 1.20 Pre-release 6, 1.20.1, 1.20.4, 23w51b
    • Confirmed
    • Entities, Networking
    • Low
    • Platform

      The bug

      Effect amplifiers are read/written as byte (-128 to 127) from/to NBT instead of an integer (-2,147,483,648 to 2,147,483,647) which is how it is stored in memory. This causes a change is behavior when the effect is reloaded from NBT is the amplifier is above 127.

      How to reproduce

      1. Give yourself jump boost with an amplifier higher than 127 using /effect 
        /effect give @s jump_boost 100 128
      2. Try to jump
        → You cannot jump (see also MC-90198)
      3. Reopen the world
        → You now have jump boost with an amplifier of -128 when read (though will be considered 0 when an amplifier obtained via NBT is less than 0)

      Code analysis

      Based on 1.12 decompiled using MCP 9.40 PRE 1

      The methods net.minecraft.potion.PotionEffect.readCustomPotionEffectFromNBT(NBTTagCompound) and net.minecraft.potion.PotionEffect.writeCustomPotionEffectToNBT(NBTTagCompound) reads/writes the amplifier as a byte, while it is stored in-memory as an integer.

        1. 2023-02-16_21-59-23.mp4
          7.15 MB
        2. 2023-02-16_21-59-23-1.mp4
          7.15 MB

            gegy1000 [Mojang] Gegy
            jirauser71590 user-f2760 (Inactive)
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              Created:
              Updated:
              Resolved:
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